Introduction to immunology
Normal function of Immune System
- defence against infection
- dysregulated, excessive or absent immune responses → pathology
- dysregulation example:
o allergies – hay fever, asthma
o autoimmune disease – type 1 diabetes, rheumatoid arthritis
o immunodeficiencies
o immunoproliferative disorders
Features of the immune response
- specificity
- memory
- self-nonself discrimination – distinguish between foreign pathogens
- ‘Redundancy’ – rely on different components in case one is not working
Types of immune response
- Innate response
o Rapid, relatively non-specific, no memory, first line of defence
- Adaptive response
o Slower, highly specific, long-lasting memory, 33ultimately more effective,
second line of defence
INNATE RESPONSE
- Skin - tough barrier to infection
- Mucosal surfaces - sticky mucus
o cilia and peristaltic flow
- Nonspecific antibacterial molecules:
o Lysozyme
o Lactoferrin
Soluble mediators
- Bind to pathogens or their products
- Opsonise pathogens for phagocytosis
- Recognise mainly bacterial carbohydrates
- F
- E.g. Collectins
o opsonise bacteria for phagocytosis
o activate complement
- Complement (alternative pathway)
o directly lyses some bacteria
o opsonises bacteria for phagocytosis
o recruits phagocytes
- Other mediators, e.g. acute phase proteins
, Cellular mediators
- Neutrophils
o phagocytic cells of acute phase response
- Macrophages
o more long-lived phagocytic cells, resident in tissues
- Dendritic cells
o long-lived cells resident in tissues; most efficient at presenting antigens
- Natural killer cells
o lymphocytes important in antiviral immunity
Phagocytic cells
- e.g. neutrophils, macrophages
- are able to bind and engulf (phagocytose) pathogens
- Use pattern recognition receptors (PRRs) that recognise bacterial, viral and fungal molecules,
e.g. scavenger and toll-like receptors
- Binding triggers adaptive immune response
Interaction between innate and adaptive immune response
- innate response ‘instructs’ the adaptive response
- Innate soluble mediators aid phagocytosis
- Phagocytes present antigens to the adaptive immune system
- Pathogen binding activates antigen presentation
ADAPTIVE IMMUNE RESPONSE
Soluble mediators
- Antibodies
o IgM, IgG, IgA, IgE
Lymphocytes
- B cells
o Produce antibodies
o Sometimes called plasma cells
- T cells
o Cell-mediated immunity
The adaptive immune response:
- Take several days to develop
- B cells produce antibodies that neutralise extracellular bacteria & viruses
- T cells respond to intracellular pathogens
- T cells required for most B cell responses
B cells and antibody production
- Naïve B cells produce IgM which is the primary response to infection
o Naïve – have not been stimulated enough to produce specific antibodies
- Specific antigen induces class switching to IgG, IgA etc.
Normal function of Immune System
- defence against infection
- dysregulated, excessive or absent immune responses → pathology
- dysregulation example:
o allergies – hay fever, asthma
o autoimmune disease – type 1 diabetes, rheumatoid arthritis
o immunodeficiencies
o immunoproliferative disorders
Features of the immune response
- specificity
- memory
- self-nonself discrimination – distinguish between foreign pathogens
- ‘Redundancy’ – rely on different components in case one is not working
Types of immune response
- Innate response
o Rapid, relatively non-specific, no memory, first line of defence
- Adaptive response
o Slower, highly specific, long-lasting memory, 33ultimately more effective,
second line of defence
INNATE RESPONSE
- Skin - tough barrier to infection
- Mucosal surfaces - sticky mucus
o cilia and peristaltic flow
- Nonspecific antibacterial molecules:
o Lysozyme
o Lactoferrin
Soluble mediators
- Bind to pathogens or their products
- Opsonise pathogens for phagocytosis
- Recognise mainly bacterial carbohydrates
- F
- E.g. Collectins
o opsonise bacteria for phagocytosis
o activate complement
- Complement (alternative pathway)
o directly lyses some bacteria
o opsonises bacteria for phagocytosis
o recruits phagocytes
- Other mediators, e.g. acute phase proteins
, Cellular mediators
- Neutrophils
o phagocytic cells of acute phase response
- Macrophages
o more long-lived phagocytic cells, resident in tissues
- Dendritic cells
o long-lived cells resident in tissues; most efficient at presenting antigens
- Natural killer cells
o lymphocytes important in antiviral immunity
Phagocytic cells
- e.g. neutrophils, macrophages
- are able to bind and engulf (phagocytose) pathogens
- Use pattern recognition receptors (PRRs) that recognise bacterial, viral and fungal molecules,
e.g. scavenger and toll-like receptors
- Binding triggers adaptive immune response
Interaction between innate and adaptive immune response
- innate response ‘instructs’ the adaptive response
- Innate soluble mediators aid phagocytosis
- Phagocytes present antigens to the adaptive immune system
- Pathogen binding activates antigen presentation
ADAPTIVE IMMUNE RESPONSE
Soluble mediators
- Antibodies
o IgM, IgG, IgA, IgE
Lymphocytes
- B cells
o Produce antibodies
o Sometimes called plasma cells
- T cells
o Cell-mediated immunity
The adaptive immune response:
- Take several days to develop
- B cells produce antibodies that neutralise extracellular bacteria & viruses
- T cells respond to intracellular pathogens
- T cells required for most B cell responses
B cells and antibody production
- Naïve B cells produce IgM which is the primary response to infection
o Naïve – have not been stimulated enough to produce specific antibodies
- Specific antigen induces class switching to IgG, IgA etc.
