Human and Veterinary Immunology
Chapter 1
Main functions:
- Protection against infectious microbes, “non-self”
* Intracellular (viruses, some bacteria and parasites)
* Extracellular (most bacteria and parasites, fungi)
- Protection against modified “self”
*Cancer/tumor cells or transformed cells
Innate immunity Adaptive immunity
Within 12 hr Within days
Phagocyte, DC, NK, ILCs, complement B- and T-lymphocytes ( antibodies)
All cells of the immune system secrete cytokines and express different receptors for the cytokines (IL
or TNF). Chemokine is a type of cytokine that is produced as a "chemo-attractant molecules" i.e.
to attract cells to sites of infection/inflammation. Cytokine is a general term used for all signalling
molecules while chemokines are specific cytokines that functions by attracting cells to sites of
infection/inflammation.
Adaptive immune response
Humoral immunity mediated by molecules in the
blood or mucosal secretions antibodies. These
are produced by B-lymphocytes. The antibodies
recognize microbial antigens, neutralize the
infectivity of the microbes and target microbes for
elimination. Humoral immunity is defense
mechanism against extracellular microbes and
their toxins.
Cell mediated immunity (cellular immunity) is
mediated by T-lymphocytes and against
intracellular microbes. Involves activation of
macrophages (MP) and natural killer cells (NK-cell)
and release of cytokines. Do not produce
antibodies.
Immunity
Active: immunity induced by exposure to a foreign antigen. The individual plays an active role in
responding to the antigen.
Passive: transferring serum or lymphocytes from a specifically immunized individual in experimental
situations. Become immune without exposure to that specific antigen. I.e. maternal antibodies by the
placenta.
1
, Antigens ↔ Immunogen
Specificity: ensures that the immune response to a microbe is targeted to that microbe (antigen).
Diversity: enables to immune system to respond to a large variety of antigens.
This occur due to different determinants or epitopes in the structure.
Clonal expansion: increase in the number of cells that express identical receptors for the antigen
(thus belong to a clone). This increase enables the A. immune response to keep pace with rapidly
dividing infectious pathogens.
Specialization: generate responses that are optimal for defense against different types of microbes.
Specificity and Memory → combat infections that occur repeatedly.
Diversity → defend against the many potential pathogens.
Specialization → enables the host to combat different types of microbes.
Contraction of the response → allows the system to return to a state of rest after it eliminates each
foreign antigen and to be prepared to respond to other antigens.
Self-tolerance → preventing harmful reactions against one’s own cells and tissue while maintaining a
diverse repertoire of lymphocytes specific for foreign antigens.
B- and T-lymphocytes
B cells produce antibodies and recognize extracellular soluble and cell surface antigens. They
differentiate into antibody secreting plasma cells and functioning as the mediator of humoral
immunity. T-cells do not produce antibodies. They help phagocytes to destroy microbes or they kill
the infected cells. T-cells recognize peptides derived from a foreign protein which are presented by
major histocompatibility complex (MHC), which are expressed on the surfaces of other cells.
T-cells
→ T-helper cells (Th)
→ Cytotoxic T-lymphocytes (CTL).
Th cells secrete cytokines in response to antigenic stimulation. They function as a messenger
molecule and stimulate proliferation and differentiation of the T-cells and activate other cells
(including B-cells, macrophages and leukocytes). CTLs kill cells that produce foreign antigens.
Regulator T cells inhibit the immune response. NKT cells that express some cell surface proteins on
NK cells.
Antigen presenting cell (APC) is a cell that
displays antigen complexed with major histocompatibility
complexes (MHCs) on their surfaces; this process is known as antigen
presentation. T cells may recognize these complexes using their T cell
receptors (TCRs). These cells process antigens and present them to T-cells.
The most specialized APC is a dendritic cell (DC). Microbial antigens that
enter from the external environment transport these antigens to lymphoid
organs and present the antigens to naïve T-lymphocytes to initiate immune
responses.
2
Chapter 1
Main functions:
- Protection against infectious microbes, “non-self”
* Intracellular (viruses, some bacteria and parasites)
* Extracellular (most bacteria and parasites, fungi)
- Protection against modified “self”
*Cancer/tumor cells or transformed cells
Innate immunity Adaptive immunity
Within 12 hr Within days
Phagocyte, DC, NK, ILCs, complement B- and T-lymphocytes ( antibodies)
All cells of the immune system secrete cytokines and express different receptors for the cytokines (IL
or TNF). Chemokine is a type of cytokine that is produced as a "chemo-attractant molecules" i.e.
to attract cells to sites of infection/inflammation. Cytokine is a general term used for all signalling
molecules while chemokines are specific cytokines that functions by attracting cells to sites of
infection/inflammation.
Adaptive immune response
Humoral immunity mediated by molecules in the
blood or mucosal secretions antibodies. These
are produced by B-lymphocytes. The antibodies
recognize microbial antigens, neutralize the
infectivity of the microbes and target microbes for
elimination. Humoral immunity is defense
mechanism against extracellular microbes and
their toxins.
Cell mediated immunity (cellular immunity) is
mediated by T-lymphocytes and against
intracellular microbes. Involves activation of
macrophages (MP) and natural killer cells (NK-cell)
and release of cytokines. Do not produce
antibodies.
Immunity
Active: immunity induced by exposure to a foreign antigen. The individual plays an active role in
responding to the antigen.
Passive: transferring serum or lymphocytes from a specifically immunized individual in experimental
situations. Become immune without exposure to that specific antigen. I.e. maternal antibodies by the
placenta.
1
, Antigens ↔ Immunogen
Specificity: ensures that the immune response to a microbe is targeted to that microbe (antigen).
Diversity: enables to immune system to respond to a large variety of antigens.
This occur due to different determinants or epitopes in the structure.
Clonal expansion: increase in the number of cells that express identical receptors for the antigen
(thus belong to a clone). This increase enables the A. immune response to keep pace with rapidly
dividing infectious pathogens.
Specialization: generate responses that are optimal for defense against different types of microbes.
Specificity and Memory → combat infections that occur repeatedly.
Diversity → defend against the many potential pathogens.
Specialization → enables the host to combat different types of microbes.
Contraction of the response → allows the system to return to a state of rest after it eliminates each
foreign antigen and to be prepared to respond to other antigens.
Self-tolerance → preventing harmful reactions against one’s own cells and tissue while maintaining a
diverse repertoire of lymphocytes specific for foreign antigens.
B- and T-lymphocytes
B cells produce antibodies and recognize extracellular soluble and cell surface antigens. They
differentiate into antibody secreting plasma cells and functioning as the mediator of humoral
immunity. T-cells do not produce antibodies. They help phagocytes to destroy microbes or they kill
the infected cells. T-cells recognize peptides derived from a foreign protein which are presented by
major histocompatibility complex (MHC), which are expressed on the surfaces of other cells.
T-cells
→ T-helper cells (Th)
→ Cytotoxic T-lymphocytes (CTL).
Th cells secrete cytokines in response to antigenic stimulation. They function as a messenger
molecule and stimulate proliferation and differentiation of the T-cells and activate other cells
(including B-cells, macrophages and leukocytes). CTLs kill cells that produce foreign antigens.
Regulator T cells inhibit the immune response. NKT cells that express some cell surface proteins on
NK cells.
Antigen presenting cell (APC) is a cell that
displays antigen complexed with major histocompatibility
complexes (MHCs) on their surfaces; this process is known as antigen
presentation. T cells may recognize these complexes using their T cell
receptors (TCRs). These cells process antigens and present them to T-cells.
The most specialized APC is a dendritic cell (DC). Microbial antigens that
enter from the external environment transport these antigens to lymphoid
organs and present the antigens to naïve T-lymphocytes to initiate immune
responses.
2
