Lecture 1
Specific, adaptive or acquired immunity
There are 2 main criteria for response:
Specificity – altered response = selective. Only one type of bacterium, virus or pollen grain can
trigger the response
Memory – a second infection occurs, the responses will be faster so tissue damage is minor.
There are 2 mechanisms of specific immunity:
Antibody mediated/humoral immunity (specificity depend on antibodies)
Cell mediated / cellular immunity (specificity depends on T cells)
ANTIGENS
- a substance capable of inducing a specific immune response
Immunogenicity VS Antigenicity
Immunogenicity = ability to induce immune response
 B cell + immunogen  effector B cells + memory B cells
 T cell + immunogen  effector T cells + memory T cells
Antigenicity = ability to combine with products of immune response
 Antibodies
 Cell-surface receptors
Immunogen always an antigen. Antigen not necessarily an immunogen.
Antigen types:
Endogenous antigens – originates inside body, recognised by cytotoxic T cells
Exogenous antigens – originates outside the body, recognised by helper T cells
Immunogenicity
Determined by 4 properties of the immunogen:
- Foreignness
- Molecular size
- Chemical composition and heterogeneity (synthetic copolymers = immunogenic, aromatic
amino acids enhance immunogenicity)
- Susceptibility to antigen processing and presentation (d-stereoisomers are not
immunogenic, insolubility increase phagocytosis and processing)
Antigen structure
Antigenic determinant (epitope) – the site on the antigen molecule where the antibody or TCR binds
non covalently. Each epitope has a small number of lymphocytes that can recognise and respond to
it. It induces the production specific antibody or T cell. Antibody binds to its only particular epitope
only.
Hapten – a molecule too small to initiate immune response, can trigger response when linked to a
carrier molecule, will react with antibody present, responsible for allergic reaction to drugs.
Antigenic not immunogenic.
Antibodies
Gamma globulins of antibodies absorbed by antigen.
Classes of antibodies:
IgG – 75% of all antibodies
only class that crosses placenta
monomers
found in
blood, lymph and intestine
protect against bacteria and viruses
triggers complement,
enhance phagocytosis, neutralise toxins
IgA – 15% of all antibodies
monomers and dimers
found in tears, saliva, mucus, milk,
blood, lymph, GI secretion
provides localised protection on mucous membranes
IgM – 10%
pentamers and monomers on B cell surface
found in blood lymph and B cell
surface as antigen receptor
causes lysis of microbes; antigen receptor on B cells; agglutinogens
on RBC; first antibody after exposure.
IgD – monomers
found in blood. Lymph, B cell surface as antigen receptor
involved in
activation of B cells
IgE – monomers
found on mast cells and basophils
involved in allergic reactions
Antibody function
Complexes neutralise or eliminate antigen by several different mechanisms:
- Activation of complement (classical pathway)
- Phagocytosis (through opsonisation)
- Neutralisation (cross linking molecules of toxin or viruses)
The immunoglobulin superfamily
- B cell receptor
- T cell receptor
- Class I and II MHC molecules
- T cell accessory proteins (CD antigens)
- Poly-Ig receptor (secretory component of IgA and IgM)
- Cell adhesion molecules (CAMs)
Monoclonal antibodies
o Normal activated antibody-producing B cell
o Fused with hybridoma (hybrid cell immortalised and antibody-producing)
o Inserted into myeloma cell(immortal cancerous plasma cell)
Lecture 4
Lymphocytes, major histocompatibility complex and antigen presenting cells.
Specific – B and T cells
Non-specific – null cells (NK cells) = all differentiate in bone marrow
Null cells mostly large granular lymphocyte. B and T cells start as small cells that migrate to specific
regions of lymphatic tissue. The have CD markers.
B lymphocytes
o Clone of original B cell formed over 4-5 days  plasma cells (Ig secretors) and memory cells
T lymphocytes
Immature t cells migrate to thymus gland  divide and differentiate into cytotoxic, helper and
regulatory cells.
Inactive T cells aggregate in lymph nodes and spleen until activated by appropriate antigens.
Recog antigens displayed on self-cells (with MHC molecules):
Th – CD4+, MHC class II - restricted
Tc – CD8+, MHC class I – restricted
Treg – ‘suppressor’ T cells subpopulations of Th and Tc
o Mostly CD4+, MHC class II – restricted
o Some CD8+, MHC class I – restricted
o Characterised by FOXP3 transcription factor
Major Histocompatibility complex
 Role in intercellular recognition and discrimination b/w self/non-self
 MHC molecules act as antigen presenting strictures  influence range of an individuals
antigen response.
 Genes linked usually inherited together but some recombination.
Antigen presenting cells
 Process and present exogenous antigens to Th cells
 B cells can recog free antigens
 Presenting means that a fragment of antigen is associated with an MHC protein and inserted
into the plasma membrane.
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