Topic 6.3: ADAPTIvE ImmunITy
ImmunITy!!
Adaptive Immunity
The adaptive immune responses share two key characteristics:
¥ They are specific (i.e. they can differentiate between different types of pathogens and respond accordingly)
¥ They are adaptive (i.e. they produce a heightened response upon re-exposure Ð there is immunological memory)
Antigen Recognition Antibodies
Antigens are substances that the body recognise as foreign Antibodies are proteins produced by B lymphocytes that are
and that can elicit an immune response specific to a given antigen (they are also called immunoglobulins)
Antigens are presented to lymphocytes via identification
Variable region
markers on the surface of native cells (MHC molecules) (binds to the antigen)
¥ MHC I markers are found on all body cells (except RBCs)
and present endogenous antigens (cell-mediated response) Heavy chain (×2)
Light chain Constant region
¥ MHC II markers are on innate immune cells (macrophages) (site for opsonisation)
(×2)
and present exogenous antigens (humoral response)
Role of Lymphocytes
Humoral Immunity (targets Ônon-self Õ) Cell Mediated Immunity (targets Ôself Õ)
¥ B cells each produce one specific type of antibody ¥ Infected cells present antigens on their MHC I markers
¥ Macrophages or dendritic cells present antigen fragments ¥ Antigens are recognised by cytotoxic T cells (and TH cells)
(via MHC II markers) to helper T lymphocytes (TH cells) ¥ Cytotoxic T lymphocytes (TC cells) bind to the infected
¥ TH cells release cytokines and activate the antigen-specific cell and trigger its destruction (via perforating enzymes)
B cells (which rapidly divide to form many plasma cells) ¥ TH cells stimulate the formation of memory TC cells
¥ The plasma cells make antibodies specific to the antigen ¥ TC cells can target virus-infected cells and tumor cells
¥ A small proportion of B cell clones differentiate into ¥ Suppressor T cells regulate the action of TC cells in order
long-lasting memory B cells (for long-term immunity) to prevent sustained T cell activation (i.e. autoreactivity)
B Cell
Pathogen Virus
Macrophage + TH Cell Infected cell + TC cell Lysed cell
antibodies
Immune System Disorders
Immunodeficiency Hypersensitivity
¥ HIV is a retrovirus that infects helper T cells (TH cells) ¥ Allergens are substances that trigger an immune response
¥ It is usually transmitted via the exchange of bodily fluids despite not being inherently harmful (e.g. peanut allergy)
(e.g. sex, breastfeeding, transfusions, injections, etc.) ¥ When a B cell is activated by an allergen, it makes large
¥ HIV is integrated into the genome of infected TH cells quantities of allergen-specific antibodies (IgE)
¥ After a prolonged period of inactivity, it becomes active ¥ These IgE antibodies bind to mast cells and ÔprimeÕ them
and lyses the TH cell as it begins to spread ¥ Upon re-exposure to the allergen, the sensitised mast cells
¥ This results in an inability to produce antibodies and a release large quantities of histamine (causes inflammation)
general loss of immunity (disease is called AIDS) ¥ This inflammatory response is called an allergic reaction
ImmunITy!!
Adaptive Immunity
The adaptive immune responses share two key characteristics:
¥ They are specific (i.e. they can differentiate between different types of pathogens and respond accordingly)
¥ They are adaptive (i.e. they produce a heightened response upon re-exposure Ð there is immunological memory)
Antigen Recognition Antibodies
Antigens are substances that the body recognise as foreign Antibodies are proteins produced by B lymphocytes that are
and that can elicit an immune response specific to a given antigen (they are also called immunoglobulins)
Antigens are presented to lymphocytes via identification
Variable region
markers on the surface of native cells (MHC molecules) (binds to the antigen)
¥ MHC I markers are found on all body cells (except RBCs)
and present endogenous antigens (cell-mediated response) Heavy chain (×2)
Light chain Constant region
¥ MHC II markers are on innate immune cells (macrophages) (site for opsonisation)
(×2)
and present exogenous antigens (humoral response)
Role of Lymphocytes
Humoral Immunity (targets Ônon-self Õ) Cell Mediated Immunity (targets Ôself Õ)
¥ B cells each produce one specific type of antibody ¥ Infected cells present antigens on their MHC I markers
¥ Macrophages or dendritic cells present antigen fragments ¥ Antigens are recognised by cytotoxic T cells (and TH cells)
(via MHC II markers) to helper T lymphocytes (TH cells) ¥ Cytotoxic T lymphocytes (TC cells) bind to the infected
¥ TH cells release cytokines and activate the antigen-specific cell and trigger its destruction (via perforating enzymes)
B cells (which rapidly divide to form many plasma cells) ¥ TH cells stimulate the formation of memory TC cells
¥ The plasma cells make antibodies specific to the antigen ¥ TC cells can target virus-infected cells and tumor cells
¥ A small proportion of B cell clones differentiate into ¥ Suppressor T cells regulate the action of TC cells in order
long-lasting memory B cells (for long-term immunity) to prevent sustained T cell activation (i.e. autoreactivity)
B Cell
Pathogen Virus
Macrophage + TH Cell Infected cell + TC cell Lysed cell
antibodies
Immune System Disorders
Immunodeficiency Hypersensitivity
¥ HIV is a retrovirus that infects helper T cells (TH cells) ¥ Allergens are substances that trigger an immune response
¥ It is usually transmitted via the exchange of bodily fluids despite not being inherently harmful (e.g. peanut allergy)
(e.g. sex, breastfeeding, transfusions, injections, etc.) ¥ When a B cell is activated by an allergen, it makes large
¥ HIV is integrated into the genome of infected TH cells quantities of allergen-specific antibodies (IgE)
¥ After a prolonged period of inactivity, it becomes active ¥ These IgE antibodies bind to mast cells and ÔprimeÕ them
and lyses the TH cell as it begins to spread ¥ Upon re-exposure to the allergen, the sensitised mast cells
¥ This results in an inability to produce antibodies and a release large quantities of histamine (causes inflammation)
general loss of immunity (disease is called AIDS) ¥ This inflammatory response is called an allergic reaction
