Adaptive immunity

Question 1

Structure of antibody

Answer 1

2 Fab arms (recognises antigen)
1 Fc region (destroys antigen)

light and heavy chains of immunoglobulin domains, joined by disulfide bridge

end terminal domains of Fab arms are variable regions
constant regions are same for antibodies of given class

Question 2

What is somatic recombination?

Answer 2

where multiple exon regions in genome recombine
-in early B cell differentiation, multiple variable exon regions recombine
-occurs randomly and imprecisely (gens muts) -> gives lots of different antibodies!

Question 3

Which antibodies exist as monomers?

Answer 3

IgG, IgD, IgE, IgA

Question 4

Which antibodies exist as polymers?

Answer 4

IgA -dimer (when secreted) -has J peptide and secretory component protein
IgM -pentamer -has J peptide

Question 5

What is class switching?

Answer 5

when a B cell switches to produce different classes of antibody after antigen stimulation
-IgM switches to IgG, IgA or IgE
-variable region stays the same but recombines with different constant region domain
-allows same specificity to be linked to different locations and Fc functions

Question 6

What is antigen maturation?

Answer 6

the increase in antibody affinity during the immune response
-variable regions undergo somatic hypermutations (lots of muts!) and the mutants that increase affinity are selected for

Question 7

Which antibodies block pathogen adherence to host?

Answer 7

IgM, IgG, IgA

Question 8

Which antibodies neutralise toxins?

Answer 8

IgG, IgA

Question 9

Which antibodies agglutinate bacteria?

Answer 9

all antibodies
IgM, IgA agglutinate most efficiently (bc they’re pentamers, dimers)

Question 10

Which antibodies block nutrient uptake?

Answer 10

IgG

Question 11

Which antibodies enhance phagocytosis?

opsonisation

Answer 11

IgG, monomeric IgA

(N/B: secretory component blocks Fc region in dimeric IgA)

Question 12

Which antibodies activate complement?

Answer 12

IgG
IgM -more efficient activator due to having more regions

-adjacent antibodies need to interact with 2 head groups of CIq

once complement activated…
-opsonisation
-inflammation
-cell lysis

Question 13

Which antibodies allow infected host cellls to express foregin proteins on their cell surfaces?

Answer 13

IgG

-allows NK cells to recognise and induce antibody-dependent cell-mediated cytotoxicity (ADCC)

Question 14

What are thymus independent (TI) antibodies?

Answer 14

antigens that induce B cell responses in absence of T cells

Question 15

What are thymus dependent (TD) antibodies?

Answer 15

antigens that require T cell help to induce B cell responses
-most antigens are TD

Question 16

What is the clonal selection hypothesis?

Answer 16

-body produces lots of diff B cells independently of infection
-bact binds to specific B cell
-“selected” B cell divides and differentiates (plasma cells)

Question 17

What are major histocompatability complexes?

Answer 17

protein complexes that transport processed antigen to host cell surface to present them to T cells
-MHC1 in all nucleated cells present to CD8 +ve cells (cytotoxic)
-MHC2 in macrophages, B cells, dendritic cells present to CD4 +ve cells (helper)

Question 18

MHC1

Answer 18

MHC expressed by all nucleated cells that present endogenous peptides (path proteins synth by infected cell) to CD8 +ve cells (cytotoxic T cells)

Question 19

MHC2

Answer 19

MHC expressed by macrophages, B cells, dendritic cells that present exogenous peptides (synth by pathogen) to CD4 +ve cells (helper T cells)

Question 20

Why are there different subsets of T helper cells?

Answer 20

-produce diff cytokines (bind to diff receptors, causing diff responses)
-ensure responses are pathogen-approprriate

eg. TH1 cells produce interferon-γ, IL-2 and TND to activate macrophages (inflamm) important in tackling extracellular bact
Treg cells produce IL-10 and TGFβ to inactivate T helper cells and suppress inflamm once infection dealt with