Humoral immunity and antibodies Flashcards
Describe the activation of naive B cells
- Similar to T cells it needs 3 signals
- 1st= antigen binds to surface and is internalised then presented
- 2nd= Antigen specific T cells bind to B cell, MHC 2 and CD4 and TCR all bind together
- 3rd= Th2 cell releases co-stimulatory cytokines which bind to B cell
What happens once a B cell is activated?
- Becomes a lymphoblast and undergoes class switching
- Clonal proliferation
- Formation of memory cells
Briefly list the stages of naive B cell activation
- Binding of antigen to surface IgM/ IgD of B cell
- Internal processing of antigen and presentation to Th cell via MHC 2
- Molecular stabilisation of complex (CD4)
- Th2 cytokine release (IL-4, IL-5)
- Proliferation of B cell clone, plasma cell formation and Ig production increases.
How do you identify a plasma cell on a microscope slide?
- Acentric nucelus
- Found in tissues/ LN not normally blood
Describe the activation of memory B cells
-Still require signals and help from Th2 cells to be activated
Describe the characteristics of memory B cells
- Have much faster antibody synthesis
- Increased affinity to Ag
- Increased expression of MHC class 2 and costim molecules
- Interact with armed t cells at lower Ag dose
What are the different regions of an Ig?
The Fab region= antigen binding site The Fc (constant) region= determines biological activity. SIGNALLING.
What are the effects of Ag-Ab complex formation?
- Opsonisation by complement (phagositation)
- Binding to FcR on phagcytes (phagocytosis)
- Persistence can damage organs (Type 3 hypersensitivity)
- Crosslinking of IgE (mast cell degranulation)
What are the effects of the antibody binding to antigens on cells?
-Recognition by NK cells leading to ADCC
What are the effects of antibody on surface of a B cell binding to antigen?
Exogenous antigen presentation to Th2 cells, promotes plasma cell formation
What determines which class (isotype) the antibody is?
-The carbohydrate pattern of the constant region
Describe the primary and secondary immune responses
- Primary: shows severe clinical signs,low magnitude, initiated in local LN, primary/ naive IR that largely involved IgM production, memory cells established
- Secondary: memory cells present so clinical signs lessened, higher magnitude, initiated in local lymphoid tissues, IgM to IgG.
Where will you mainly find IgA?
Mucous membranes
Where will you mainly find IgG?
Serum and transudates into tissues
What does the presence of IgM indicate?
Acute phase of the antibody response to an antigen/ pathogen
Describe passive immunity
- In neonates, colostrum ingested (12-36hrs post birth)
- After this the gut is no long patent to transfer of antibiotics
- ## Maternal antibodies in colostrum either remain high in gut (IgA) or transferred across gut epithelium (IgG).
Describe the contents of colostrum
- IgG (major component)
- IgA (protects gut epithelium against bacterial invasion)
- IgM/ IgE
- Cytokines
- Trypsin inhibitors
- Lymphocytes (mainly T cells)
How is IgG transported across gut epithelium in neonates?
-IgG transport protein (FcRn) expressed on gut epithelium
-2 molecules of FcRn bind one molecule of IgG
-Bind via Fc portion of IgG
-Endocytosis to reach local capillaries
(ACTIVE TRANSPORT)
- Can also transudate across
List some factors that influence success of passive immunity
- Type of placenta
- Infection/ vaccination record of mother
- Maternal immune response to vaccines
- Quality/ quantity of colostrum
- Number of young
Which placental types have no transfer of IgG and so the neonates are completely reliant on colostrum?
- Syndesmochorial (calf, lamb)
- Epitheliochorial (foal, piglet)
What tests can you use to measure Ig transfer?
- Latex agglutination
- Turbidity test
What is serconversion?
The increase in titres of antibody from baseline levels. Commonly used diagnostically.
