Humoral immunity Flashcards
3 functions of antibodies
Neutralisation, Opsonisation, Complement activation
Difference between antibody affinity and avidity
Affinity: strength of interaction between epitope and Ab’s Ag binding site
Avidity: overall strength of Ab:Ag complex. Depends on affinity + number of antigen binding sites on Ab
Structure of antibody
Variable region: many many forms
Constant region: 2x
2 light chains (lamda, kappa)
1 heavy chain (micro, delta, gamma, alpha, epsilon)
Which is the first antibody made in B cell
IgM (largest antibody, remains in blood to kill pathogens)
Which is the main antibody in blood
IgG
Which antibody is mainly found in body fluids
IgA
Which antibody remains membrane bound, regulates cell’s activation
IgD
Which antibody is found in trace amount in bloods, triggers allergic reactions
IgE
Describe primary humoral immune response
- DC move from infection site to lymph node
- T cell activated by DC
- Circulating B cells trapped at T cell zone border, activated by Th2 cell
- B cell moves to primary follicle, forms germinal centre
- Some B cells differentiate into plasma cells and secrete immunoglobulin, some continue to proliferate with T cells.
- Clonal expansion and Somatic hypermutation occurs
What co-receptor do all B cells express
CD19
What is an epitope
Structure recognised by antibody e.g. viral coat proteins
Describe recirculation of lymphocytes
- Naive B cell and CD4 T helper cell find each other in lymph node.
- B cell recirculates from blood through lymph node through primary follicle
- If it doesn’t interact with T cell with same specificity: will recontinue recirculation
- If it binds to Ag to T cell zone: proliferates, produces igM, undergoes somatic hypermutation and class switching
Which antibody crosses the placenta
IgG
Which antibody is most prevalent in breast milk
IgA.
But note that all Ig are secreted in breast milk.
Note: IgA from breast milk stays in baby’s gut, won’t enter blood.
Describe thymus dependent B cell activation
- BCR (membrane bound Ig) binds to cognate antigen, clustering of Ig receptors
- T cell sends signal to activate B cell
(T helper cells that recognise peptide:MHC complex activate B cell)
Describe thymus independent B cell activation
- BCR binds to cognate antigen
2. Direct recognition of pathogen by toll-like receptors OR extensive BCR cross linking
Describe Thymus independent Type 1 response + antigens it works against
Directly activates B cells via toll-like receptors (no need T cells)
In high Ag conc: non-antigen specific, can stimulate multiple B cells against multiple antigens
In low Ag conc: antigen specifc
ANTIGENS: LPS, bacterial DNA
Describe Thymus independent Type 2 response + antigens it works against
Multiple cross linking of BCR. Only activates mature B lymphocytes.
Children don’t have effective type 2 response cos majority of B cell population is immature
ANTIGENS: epitopes of encapsulated bacteria
Significance of giving children <2y conjugated vaccines (instead of pure polysaccharide vaccine)
Induces TI-type 1 response.
Polysaccharide would induce TI-type 2 response, not consistently immunogenic in children. Plus high Ag conc leads to non-antigen specific response.
Which of the following are NOT contraindications to vaccination:
- acute fever
- live vaccine for pregnant woman
- child being breast fed
- premature child
- previous hx of pertussis, M, M, or R infection
NOT contraindications
- child being breast fed
- premature child (need even more due to lack of maternal antibody)
- previous hx of pertussis, M, M, or R infection
