FOCUS OF THIS STUDY UNIT 1
• When and how did the Aids epidemic start?
• Where and when did the HI virus originate?
• Prevalence and incidence of the epidemic
• Responses to the Aids epidemic.
STUDY PAGES 4-18 OF TEXTBOOK
In order to structure our focus on this study unit, we'll start with the Mementoes and skills to take home at the end of study unit 1 of the
study guide.
Narrate the early history of HIV and its discovery
In June 1981 the world became aware of a new disease with a rare form of pneumonia and a rare form as cancer as symptoms. It was
initially linked to 5 homosexual men, but at the end of 1981 included haemophiliacs and injecting drug users. The disease was soon
also identified amongst heterosexual people in Central Africa, where it was called the 'slim disease' because of severe weight loss and
diarrhoea. Scientists knew that this disease damaged the immune system.
This new disease was named Aids (Acquired Immunodeficiency Syndrome) in 1982. Luc Montagnier discovered the HI virus in 1983
and it became known as the Human Immunodeficiency Virus, abbreviated as HIV. Aids was first reported in SA in 1983 with two
homosexual men being diagnosed. During those early years, Aids was linked to homosexual men, haemophiliacs and blood
transfusions. Only by the end of 1989 entry into the heterosexual world was confirmed, where after Aids spread rapidly worldwide.
Two scientists, i.e. Montagnier (from the Pasteur Institute in Paris) and Gallo (an American) both claimed that they discovered the HI
virus first. This resulted in court cases. The Nobel prize for medicine was awarded to scientists of the Pasteur Institute in 2008. The
laboratory of Gallo played an important role in the development of the first HIV antibody tests which became available in 1985
NB: AIDS IS ACQUIRED, NOT INHERITED - ENTERS THE BODY FROM OUTSIDE. IMMUNODEFICIENCY REFERS TO THE FACT
THAT THE IMMUNE SYSTEM IS UNABLE TO DEFEND ITSELF AGAINST INFECTIONS. SYNDROME IS A MEDICAL TERM FOR A
COLLECTION OF SPECIFIC SYMPTOMS THAT ARE CHARACTERISTIC OF A PARTICULAR CONDITION.
Explain how HIV crossed the species barrier from various primates
It was discovered that HIV (human virus) was related to SIV (simian immunodeficiency virus found in primates). Similarities between
HIV and SIV: 1) both retroviruses (will be discussed in chapter 2); 2) HIV and SIV belong to genus Lentivirus (slow virus, since it takes
a long time after infection to develop.
The different types and subtypes of the HI virus are discussed. Take note of the following (always in exam paper)
HIV-1 subtype C dominates in Southern Africa
HIV Type 2 is mostly restricted to West Africa
HIV-2 is structurally similar to HIV-1, but less pathogenic since progression to disease is slowerr
Crossing the barrier: An ancestor of HIV-1 group M was transmitted from a chimpanzee around 1930 in equatorial West Africa where
primates were often hunted. The assumption is that the virus was transmitted from the chimp to the human hunter through being bitten
or cut during hunting the animal (NOT through eating). Not certain how SIV transformed into HIV after infection; through natural
selection the virus can infect, live and reproduce in the T cells of a human.
Take note of FIV - feline immunodeficiency virus - affect cats, NOT humans. May appear in a MQC.
Explain the main differences between scientific theories and urban legends and rumours
Urban legends regarding the origin of HIV often consist of unsubstantiated conspiracy theories or stories that blame somebody, some
organisation, or government agency for manufacturing or spreading the virus. These theories are born out of fear and make people
think that they have power over their situation by placing the blame elsewhere. Examples....p 5 study guide (New Age movement,
Wouter Basson)
,Scientific theories are based on research. Counsellors should develop a critical attitude (the basic principle of scientific thinking) by
considering and evaluating options. Scientists do not always agree; different theories were considered during the early years of the
epidemic; all based on research.
Explain the difference between prevalence and incidence of HIV and how prevalence is measured and calculated
Sub Saharan Africa is area most heavily affected by the epidemic, hosting 9 countries with the highest HIV prevalence in the world.
Swaziland, Botswana, Lesotho, Zimbabwe..... South Africa is the country with the largest population of people living with HIV in the
world, i.e. 5.7 million(prevalence) and it contributes to +- 17% of the global number of HIV infections.
HIV INCIDENCE - is the percentage of NEW cases of infection in a defined period of time, i.e. the rate of infection. Divide the number of
new infections by the number of previously uninfected people. Difficult and expensive to follow a cohort of people over time. Therefore
most incidence estimates are obtained through mathematical and statistical modelling.
HIV PREVALENCE - is the percentage of people with HIV as a proportion of the total population (frequency, how common is HIV
infection). Nationalestimates (cannot be accurate) are based on
1. Data from a combination or surveys (e.g. antenatal clinic surveillance where blood is taken from pregnant women to test for
their blood group, Rheses factor, syphilis and HIV).
2. National household surveys.
3. Surveys conducted with specific groups
Standard error in statistics: since the estimates cannot be exact. it is followed by a minimum and maximum figure between which the
prevalence could actually range. Eg. 'an estimated 33.4 million (31.1 - 35.8 million) people worldwide were living with HIV in 2008'.
Narrate the main events about the history of HIV and Aids and how people reacted to the epidemic
Table 1.1 (pages 12 - 17 of the prescribed textbook) provides a summary of all the major events regarding the Aids pandemic. It will be
interesting to do the activity on page 18 to place yourself during this period.
The world's response to the Aids epidemic was one of denial, blaming and moralising. In South Africa the response to Aids was tainted
by government inaction, pseudo(false)science, denial, conflict and harmful practices. The creation of the National Aids Convention of
South Africa in 1993 was the first major step forward. Post 1994 the Mandela government - too many challenges in the newly
developed democracy and Aids, as well as TB, did not get the required attention. Refused to provide AZT to pregnant women in 1998
too prevent mother-to-child transmission.Treatment Action Campaign was established in 1998. Mbeki era: believed that HIV does not
cause Aids. Minister of health of the time refused to approve ART (antiretroviral theraphy) for pregnant women. During the years when
ART was not accessible to South Africans, positive results were documented in developed countries. In 1994 AZT, the first drug to be
used for antiretroviral therapy, was recommended to HIV+ women in the USA and infant infections began to fall. HAART (highly
effective antiretroviral therapy), a combination of antiretroviral therapies, was introduced in 1995. In 1997 death due to Aids started to
decline. SA high court ordered government in 2002 to provide nevirapine to pregnant women. From 2003 ART was available to all
South Africans who visited public health services. BUT harm done by Dr Msimang who supported unlicensed vitamin supplements and
promoted vegetables as an alternative for ART. New clinical guidelines for the management of HIV and Aids in adults, adolescents and
children, as well as guidelines to prevent mother-to-child transmission was implemented on 1 April 2010. The Health Department also
launched a major HIV counselling and testing campaign in 2010. Despite the initial obstacles, SA now has the largest antiretroviral
therapy programme in the world with a 50% coverage in 2009.
WHAT IS BEING DONE AT THE MOMENT?
• Currently vaccine research is ongoing, since it will be the most effective way of preventing HIV infection.
• South Africa is on the forefront of developing an effective microbicide (vaginal cream or gel) to prevent HIV infection in women.
• Male circumcision is encouraged, since research has shown that the risk of HIV infection can be reduced by +- 60% in men
who have been circumcised.
Test your understanding (page 18 textbook)
Note that the Nobel prize for medicine (2008) was not shared by Gallo who also claimed that he discovered the virus. It was the
Frenchmen Montagnier and Barré-Sinnousi who was honoured for their discovery of the HI virus.Hausen shared the prize with them for
his discovery of the human papilloma viruses which cause cervical cancer.
The other questions have been covered in the section above.
,FOCUS OF THIS STUDY UNIT 2
• The Immune system: different lines of defence
• How the Immune system fails in the case of HIV
• How viruses work in general
• Unique features of HIV
• HIV infection and replication
• Variability and sub-types of HIV
• Different responses to HIV infection
Study pages 20 - 36 of prescribed book.
The content of this unit contains rather complicated concepts and processes. I'll try to make it as easily understandable as possible.
PLEASE ENSURE THAT YOU KNOW ALL THE KEY TERMS USED IN THIS UNIT. I DESCRIBE ALL OF THEM BRIEFLY
Active immunity: Can be ensured by vaccination. When an individual has been infected by a pathogen, the immune system
'remembers' the specific invader through memory T and B cells. The individual thus becomes immune to that particular pathogen and
won't contract the same disease a second time. Thus long-term immunity.
Passive immunity: Is short-terms immunity that newborn babies get from their mothers through the placenta and colostrum (1st breast
milk) since they do not yet have their own antibodies to fight off infections. This immunity lasts until at most for a few months until the
baby's body can start to produce its own antibodies.
Non-specific defences: The body has a skin that protects the individual by trying to prevent a pathogen from entering the body. This is
called 'the first line of defence'' or non-specific defences. We inherit the 'second line of defence' , also called the innate immune system,
from our parents. Lookout guards, know as phagocytes (eating cells) are on the lookout for pathogens en swallow them. The innate
immune system is also non-specific.
Specific defences: The 3rd line of defence is specific. Specialist forces of the immune system are geared towards attacking and killing
one type of enemy only. This line of defence is also called adaptive or acquired immune system, since the specialist guards did not
inherit their attributes, but had to be adapted to a specific enemy by acquiring specific skills.
Cells: All living matter is made up of small units called cells. Thousands or even millions of different cells are specialised to perform
different functions. Eg. lymphocytes occur in the lymphatic system of the body. Cells are always surrounded by an outer membrane
which controls the amount and type of fluids and nutrients that enter and leave the cell. See figure 2.2 on page 23 of textbook for a
diagram of a cell. Each cell has an inner core, the nucleus, surrounded by a second membrane. Inside the core (nucleus) of the cell is
the genetic material (genome) of the cell consisting of DNA. The DNA has the 'building plan' of the whole organism in genetic code.
The cell is programmed by this genetic code to replace itself when it becomes old. Each cell in our bodies is replaced a number of times
in our lifetime.
Proteins: Large molecules made up of chains of amino acids. Each species has its own genetic code which enable them to
manufacture unique specie specific proteins, called antigens (antibody generating proteins). The immune system use the antigens of a
pathogen to recognise foreign pathogens from outside the body AND to manufacture or mobilise immune cells that can destroy the
pathogens.
Pathogens: Viruses, bacteria, fungi, micro-organisms and protozoa.
HIV subtypes: See figure 1.1 on p6. HIV strains can be classified into three groups, namely group M (major group), group O (outlier
group) and group N (non-M non-O group). Group M is the main group behind the global pandemic. In different parts of the world,
different sub-types predominate.
• HIV-1 subtype C: Southern Africa, India and China.
• HIV-1 subtype A: East and West Africa.
• HIV-1 subtype D: Parts of East Africa.
• HIV-1 subtype B: Europe, North America, Japan and Australia.
• HIV-2 are LESS pathogenic than HIV-1 and largely restricted to West Africa.
Antibody: Special protein complexes produced by the immune system to attack and neutralise specific disease-causing organisms.
DNA: Is found in the nucleus of the cell and contains all the genetic material of the organism. It basically gives instructions (codes for)
what proteins must be manufactured by each cell to sustain life. Refer to details under 'cells' above.
, RNA: With rare exception RNA Is mostly found in the cytoplasm of the cell. It's main function is to act as a messenger between the
DNA and the various protein manufacturing structures in the cell. It is also involved in certain genetic functions.
Reverse transcriptase: An enzyme which retroviruses produce and use to transform their viral RNA into proviral DNA in the replication
process.
T-cells: All immune cells manufactured by the thymus gland are called T cells. T cells cannot recognise pathogens if their antigens
have not first been processed into smaller pieces. These smaller pieces (also called epitopes) are then introduced to the T cells by
antigen-presenting cells (APC's).
B-cells: All immune cells manufactured by the bone marrow are called B cells or B lymphocytes. They are located in the lymph nodes
and their function is to manufacture munitions or weapons for the immune system.
CD4+T cells (helper T cells): These are the main regulatory cells of the immune system, referred to as the 'generals' of the immune
system. CD4+T cells regulate both the innate and the acquired immune responses and help to determine which types of immune
response the body needs to muster (or mobilise) to fight a particular pathogen. Note that the CD4+T cells do not attack or kill
pathogens themselves; instead they organise the body's army to fitihs the invading pathogens.
CD8+T cells (killer T cells): When activated as part of the immune response, these cells directly bind with infected cells, which carry
foreign antigens on their surfaces. The killer T cells release cytotoxins which form holes in the infected cell's membrane. This allows
ions, water and toxins to enter the cell, killing it and thus preventing pathogens to replicate.
Phagocytes: Often referred to as the 'scavengers' of the immune system. They are white blood cells that engulf and destroy foreign or
infected cells.
Macrophages: Types of phagocytes that generally attack cells infected with viruses. Macrophages present antigens to the lymphocytes
and thus mobilise them to attack the invaders.
Vaccine: A vaccine is a substance that simulates an infection by a specific pathogen. Through vaccination (immunisation) a protein
component of the relevant organism is transferred/produced to the immune system which then stimulates it to produce memory B and
memory T cells, similar to a true infection. Vaccines thus mimic the process in which the immune system interacts with an infection. In
the case of the HI virus, vaccine is ineffective. The virus changes so quickly that almost as soon as a vaccine has been produced, it has
already become ineffective against the new strains of viruses which have emerged.
Seroconversion: This refers to the point at which a person's HIV status converts or changes from being HIV negative to HIV positive.
This coincides with the time when an HIV test will show that a person is HIV positive. Seroconversion usually occurs 4 - 8 weeks after
an individual has been infected with the HI virus.
We continue with the TEST YOUR UNDERSTANDING section at the end of chapter 2.
What makes HIV different from other viruses?
HIV is a retrovirus, since it has RNA instead of the usual DNA in its nucleus. The nucleus is cone shaped; main feature by which the HI
virus can be recognised through a microscope. Another difference between the HI virus and other viruses, is that HIV is able to directly
attack and infect the most important defensive cells of the human immune system, i,e. the CD4+T cells. By doing so, the number of
healthy CD4+T cells in the body is reduced and the immune system is weakened.
Why are CD4+T cells called the generals of the immune system?
Already discussed above.
Why are antibodies infective against HIV?
The antibodies that the body creates in response to the HI virus are powerless to protect the body against the long-term destructive
effects of the HI virus. This retrovirus change or mutate so fast with the antigens on their surfaces, that the previously produced
antibodies no longer fit into the antigens of the virus. Try and visualise a lock and a key, with the lock changing position. The key won't
fit into the lock any more. If the structure of the antigens changes, the antibody cannot attach to it and then the host's immune
protection system cannot function.
What is the role of the antigen-presenting cells or APCs? Can you name a few APCs?
Some cells of the innate immune system act as antigen-presenting cells that grab part of an intigen (called an epitope) from one of the
invaders and display this on their own surfice. They then continue by presenting this antigen to the T cells. T cells cannot recognise
• When and how did the Aids epidemic start?
• Where and when did the HI virus originate?
• Prevalence and incidence of the epidemic
• Responses to the Aids epidemic.
STUDY PAGES 4-18 OF TEXTBOOK
In order to structure our focus on this study unit, we'll start with the Mementoes and skills to take home at the end of study unit 1 of the
study guide.
Narrate the early history of HIV and its discovery
In June 1981 the world became aware of a new disease with a rare form of pneumonia and a rare form as cancer as symptoms. It was
initially linked to 5 homosexual men, but at the end of 1981 included haemophiliacs and injecting drug users. The disease was soon
also identified amongst heterosexual people in Central Africa, where it was called the 'slim disease' because of severe weight loss and
diarrhoea. Scientists knew that this disease damaged the immune system.
This new disease was named Aids (Acquired Immunodeficiency Syndrome) in 1982. Luc Montagnier discovered the HI virus in 1983
and it became known as the Human Immunodeficiency Virus, abbreviated as HIV. Aids was first reported in SA in 1983 with two
homosexual men being diagnosed. During those early years, Aids was linked to homosexual men, haemophiliacs and blood
transfusions. Only by the end of 1989 entry into the heterosexual world was confirmed, where after Aids spread rapidly worldwide.
Two scientists, i.e. Montagnier (from the Pasteur Institute in Paris) and Gallo (an American) both claimed that they discovered the HI
virus first. This resulted in court cases. The Nobel prize for medicine was awarded to scientists of the Pasteur Institute in 2008. The
laboratory of Gallo played an important role in the development of the first HIV antibody tests which became available in 1985
NB: AIDS IS ACQUIRED, NOT INHERITED - ENTERS THE BODY FROM OUTSIDE. IMMUNODEFICIENCY REFERS TO THE FACT
THAT THE IMMUNE SYSTEM IS UNABLE TO DEFEND ITSELF AGAINST INFECTIONS. SYNDROME IS A MEDICAL TERM FOR A
COLLECTION OF SPECIFIC SYMPTOMS THAT ARE CHARACTERISTIC OF A PARTICULAR CONDITION.
Explain how HIV crossed the species barrier from various primates
It was discovered that HIV (human virus) was related to SIV (simian immunodeficiency virus found in primates). Similarities between
HIV and SIV: 1) both retroviruses (will be discussed in chapter 2); 2) HIV and SIV belong to genus Lentivirus (slow virus, since it takes
a long time after infection to develop.
The different types and subtypes of the HI virus are discussed. Take note of the following (always in exam paper)
HIV-1 subtype C dominates in Southern Africa
HIV Type 2 is mostly restricted to West Africa
HIV-2 is structurally similar to HIV-1, but less pathogenic since progression to disease is slowerr
Crossing the barrier: An ancestor of HIV-1 group M was transmitted from a chimpanzee around 1930 in equatorial West Africa where
primates were often hunted. The assumption is that the virus was transmitted from the chimp to the human hunter through being bitten
or cut during hunting the animal (NOT through eating). Not certain how SIV transformed into HIV after infection; through natural
selection the virus can infect, live and reproduce in the T cells of a human.
Take note of FIV - feline immunodeficiency virus - affect cats, NOT humans. May appear in a MQC.
Explain the main differences between scientific theories and urban legends and rumours
Urban legends regarding the origin of HIV often consist of unsubstantiated conspiracy theories or stories that blame somebody, some
organisation, or government agency for manufacturing or spreading the virus. These theories are born out of fear and make people
think that they have power over their situation by placing the blame elsewhere. Examples....p 5 study guide (New Age movement,
Wouter Basson)
,Scientific theories are based on research. Counsellors should develop a critical attitude (the basic principle of scientific thinking) by
considering and evaluating options. Scientists do not always agree; different theories were considered during the early years of the
epidemic; all based on research.
Explain the difference between prevalence and incidence of HIV and how prevalence is measured and calculated
Sub Saharan Africa is area most heavily affected by the epidemic, hosting 9 countries with the highest HIV prevalence in the world.
Swaziland, Botswana, Lesotho, Zimbabwe..... South Africa is the country with the largest population of people living with HIV in the
world, i.e. 5.7 million(prevalence) and it contributes to +- 17% of the global number of HIV infections.
HIV INCIDENCE - is the percentage of NEW cases of infection in a defined period of time, i.e. the rate of infection. Divide the number of
new infections by the number of previously uninfected people. Difficult and expensive to follow a cohort of people over time. Therefore
most incidence estimates are obtained through mathematical and statistical modelling.
HIV PREVALENCE - is the percentage of people with HIV as a proportion of the total population (frequency, how common is HIV
infection). Nationalestimates (cannot be accurate) are based on
1. Data from a combination or surveys (e.g. antenatal clinic surveillance where blood is taken from pregnant women to test for
their blood group, Rheses factor, syphilis and HIV).
2. National household surveys.
3. Surveys conducted with specific groups
Standard error in statistics: since the estimates cannot be exact. it is followed by a minimum and maximum figure between which the
prevalence could actually range. Eg. 'an estimated 33.4 million (31.1 - 35.8 million) people worldwide were living with HIV in 2008'.
Narrate the main events about the history of HIV and Aids and how people reacted to the epidemic
Table 1.1 (pages 12 - 17 of the prescribed textbook) provides a summary of all the major events regarding the Aids pandemic. It will be
interesting to do the activity on page 18 to place yourself during this period.
The world's response to the Aids epidemic was one of denial, blaming and moralising. In South Africa the response to Aids was tainted
by government inaction, pseudo(false)science, denial, conflict and harmful practices. The creation of the National Aids Convention of
South Africa in 1993 was the first major step forward. Post 1994 the Mandela government - too many challenges in the newly
developed democracy and Aids, as well as TB, did not get the required attention. Refused to provide AZT to pregnant women in 1998
too prevent mother-to-child transmission.Treatment Action Campaign was established in 1998. Mbeki era: believed that HIV does not
cause Aids. Minister of health of the time refused to approve ART (antiretroviral theraphy) for pregnant women. During the years when
ART was not accessible to South Africans, positive results were documented in developed countries. In 1994 AZT, the first drug to be
used for antiretroviral therapy, was recommended to HIV+ women in the USA and infant infections began to fall. HAART (highly
effective antiretroviral therapy), a combination of antiretroviral therapies, was introduced in 1995. In 1997 death due to Aids started to
decline. SA high court ordered government in 2002 to provide nevirapine to pregnant women. From 2003 ART was available to all
South Africans who visited public health services. BUT harm done by Dr Msimang who supported unlicensed vitamin supplements and
promoted vegetables as an alternative for ART. New clinical guidelines for the management of HIV and Aids in adults, adolescents and
children, as well as guidelines to prevent mother-to-child transmission was implemented on 1 April 2010. The Health Department also
launched a major HIV counselling and testing campaign in 2010. Despite the initial obstacles, SA now has the largest antiretroviral
therapy programme in the world with a 50% coverage in 2009.
WHAT IS BEING DONE AT THE MOMENT?
• Currently vaccine research is ongoing, since it will be the most effective way of preventing HIV infection.
• South Africa is on the forefront of developing an effective microbicide (vaginal cream or gel) to prevent HIV infection in women.
• Male circumcision is encouraged, since research has shown that the risk of HIV infection can be reduced by +- 60% in men
who have been circumcised.
Test your understanding (page 18 textbook)
Note that the Nobel prize for medicine (2008) was not shared by Gallo who also claimed that he discovered the virus. It was the
Frenchmen Montagnier and Barré-Sinnousi who was honoured for their discovery of the HI virus.Hausen shared the prize with them for
his discovery of the human papilloma viruses which cause cervical cancer.
The other questions have been covered in the section above.
,FOCUS OF THIS STUDY UNIT 2
• The Immune system: different lines of defence
• How the Immune system fails in the case of HIV
• How viruses work in general
• Unique features of HIV
• HIV infection and replication
• Variability and sub-types of HIV
• Different responses to HIV infection
Study pages 20 - 36 of prescribed book.
The content of this unit contains rather complicated concepts and processes. I'll try to make it as easily understandable as possible.
PLEASE ENSURE THAT YOU KNOW ALL THE KEY TERMS USED IN THIS UNIT. I DESCRIBE ALL OF THEM BRIEFLY
Active immunity: Can be ensured by vaccination. When an individual has been infected by a pathogen, the immune system
'remembers' the specific invader through memory T and B cells. The individual thus becomes immune to that particular pathogen and
won't contract the same disease a second time. Thus long-term immunity.
Passive immunity: Is short-terms immunity that newborn babies get from their mothers through the placenta and colostrum (1st breast
milk) since they do not yet have their own antibodies to fight off infections. This immunity lasts until at most for a few months until the
baby's body can start to produce its own antibodies.
Non-specific defences: The body has a skin that protects the individual by trying to prevent a pathogen from entering the body. This is
called 'the first line of defence'' or non-specific defences. We inherit the 'second line of defence' , also called the innate immune system,
from our parents. Lookout guards, know as phagocytes (eating cells) are on the lookout for pathogens en swallow them. The innate
immune system is also non-specific.
Specific defences: The 3rd line of defence is specific. Specialist forces of the immune system are geared towards attacking and killing
one type of enemy only. This line of defence is also called adaptive or acquired immune system, since the specialist guards did not
inherit their attributes, but had to be adapted to a specific enemy by acquiring specific skills.
Cells: All living matter is made up of small units called cells. Thousands or even millions of different cells are specialised to perform
different functions. Eg. lymphocytes occur in the lymphatic system of the body. Cells are always surrounded by an outer membrane
which controls the amount and type of fluids and nutrients that enter and leave the cell. See figure 2.2 on page 23 of textbook for a
diagram of a cell. Each cell has an inner core, the nucleus, surrounded by a second membrane. Inside the core (nucleus) of the cell is
the genetic material (genome) of the cell consisting of DNA. The DNA has the 'building plan' of the whole organism in genetic code.
The cell is programmed by this genetic code to replace itself when it becomes old. Each cell in our bodies is replaced a number of times
in our lifetime.
Proteins: Large molecules made up of chains of amino acids. Each species has its own genetic code which enable them to
manufacture unique specie specific proteins, called antigens (antibody generating proteins). The immune system use the antigens of a
pathogen to recognise foreign pathogens from outside the body AND to manufacture or mobilise immune cells that can destroy the
pathogens.
Pathogens: Viruses, bacteria, fungi, micro-organisms and protozoa.
HIV subtypes: See figure 1.1 on p6. HIV strains can be classified into three groups, namely group M (major group), group O (outlier
group) and group N (non-M non-O group). Group M is the main group behind the global pandemic. In different parts of the world,
different sub-types predominate.
• HIV-1 subtype C: Southern Africa, India and China.
• HIV-1 subtype A: East and West Africa.
• HIV-1 subtype D: Parts of East Africa.
• HIV-1 subtype B: Europe, North America, Japan and Australia.
• HIV-2 are LESS pathogenic than HIV-1 and largely restricted to West Africa.
Antibody: Special protein complexes produced by the immune system to attack and neutralise specific disease-causing organisms.
DNA: Is found in the nucleus of the cell and contains all the genetic material of the organism. It basically gives instructions (codes for)
what proteins must be manufactured by each cell to sustain life. Refer to details under 'cells' above.
, RNA: With rare exception RNA Is mostly found in the cytoplasm of the cell. It's main function is to act as a messenger between the
DNA and the various protein manufacturing structures in the cell. It is also involved in certain genetic functions.
Reverse transcriptase: An enzyme which retroviruses produce and use to transform their viral RNA into proviral DNA in the replication
process.
T-cells: All immune cells manufactured by the thymus gland are called T cells. T cells cannot recognise pathogens if their antigens
have not first been processed into smaller pieces. These smaller pieces (also called epitopes) are then introduced to the T cells by
antigen-presenting cells (APC's).
B-cells: All immune cells manufactured by the bone marrow are called B cells or B lymphocytes. They are located in the lymph nodes
and their function is to manufacture munitions or weapons for the immune system.
CD4+T cells (helper T cells): These are the main regulatory cells of the immune system, referred to as the 'generals' of the immune
system. CD4+T cells regulate both the innate and the acquired immune responses and help to determine which types of immune
response the body needs to muster (or mobilise) to fight a particular pathogen. Note that the CD4+T cells do not attack or kill
pathogens themselves; instead they organise the body's army to fitihs the invading pathogens.
CD8+T cells (killer T cells): When activated as part of the immune response, these cells directly bind with infected cells, which carry
foreign antigens on their surfaces. The killer T cells release cytotoxins which form holes in the infected cell's membrane. This allows
ions, water and toxins to enter the cell, killing it and thus preventing pathogens to replicate.
Phagocytes: Often referred to as the 'scavengers' of the immune system. They are white blood cells that engulf and destroy foreign or
infected cells.
Macrophages: Types of phagocytes that generally attack cells infected with viruses. Macrophages present antigens to the lymphocytes
and thus mobilise them to attack the invaders.
Vaccine: A vaccine is a substance that simulates an infection by a specific pathogen. Through vaccination (immunisation) a protein
component of the relevant organism is transferred/produced to the immune system which then stimulates it to produce memory B and
memory T cells, similar to a true infection. Vaccines thus mimic the process in which the immune system interacts with an infection. In
the case of the HI virus, vaccine is ineffective. The virus changes so quickly that almost as soon as a vaccine has been produced, it has
already become ineffective against the new strains of viruses which have emerged.
Seroconversion: This refers to the point at which a person's HIV status converts or changes from being HIV negative to HIV positive.
This coincides with the time when an HIV test will show that a person is HIV positive. Seroconversion usually occurs 4 - 8 weeks after
an individual has been infected with the HI virus.
We continue with the TEST YOUR UNDERSTANDING section at the end of chapter 2.
What makes HIV different from other viruses?
HIV is a retrovirus, since it has RNA instead of the usual DNA in its nucleus. The nucleus is cone shaped; main feature by which the HI
virus can be recognised through a microscope. Another difference between the HI virus and other viruses, is that HIV is able to directly
attack and infect the most important defensive cells of the human immune system, i,e. the CD4+T cells. By doing so, the number of
healthy CD4+T cells in the body is reduced and the immune system is weakened.
Why are CD4+T cells called the generals of the immune system?
Already discussed above.
Why are antibodies infective against HIV?
The antibodies that the body creates in response to the HI virus are powerless to protect the body against the long-term destructive
effects of the HI virus. This retrovirus change or mutate so fast with the antigens on their surfaces, that the previously produced
antibodies no longer fit into the antigens of the virus. Try and visualise a lock and a key, with the lock changing position. The key won't
fit into the lock any more. If the structure of the antigens changes, the antibody cannot attach to it and then the host's immune
protection system cannot function.
What is the role of the antigen-presenting cells or APCs? Can you name a few APCs?
Some cells of the innate immune system act as antigen-presenting cells that grab part of an intigen (called an epitope) from one of the
invaders and display this on their own surfice. They then continue by presenting this antigen to the T cells. T cells cannot recognise
