Adaptive immunity Flashcards
Structure of antibody
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
What is somatic recombination?
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!
Which antibodies exist as monomers?
IgG, IgD, IgE, IgA
Which antibodies exist as polymers?
IgA -dimer (when secreted) -has J peptide and secretory component protein
IgM -pentamer -has J peptide
What is class switching?
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
What is antigen maturation?
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
Which antibodies block pathogen adherence to host?
IgM, IgG, IgA
Which antibodies neutralise toxins?
IgG, IgA
Which antibodies agglutinate bacteria?
all antibodies
IgM, IgA agglutinate most efficiently (bc they’re pentamers, dimers)
Which antibodies block nutrient uptake?
IgG
Which antibodies enhance phagocytosis?
opsonisation
IgG, monomeric IgA
(N/B: secretory component blocks Fc region in dimeric IgA)
Which antibodies activate complement?
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
Which antibodies allow infected host cellls to express foregin proteins on their cell surfaces?
IgG
-allows NK cells to recognise and induce antibody-dependent cell-mediated cytotoxicity (ADCC)
What are thymus independent (TI) antibodies?
antigens that induce B cell responses in absence of T cells
What are thymus dependent (TD) antibodies?
antigens that require T cell help to induce B cell responses
-most antigens are TD
What is the clonal selection hypothesis?
-body produces lots of diff B cells independently of infection
-bact binds to specific B cell
-“selected” B cell divides and differentiates (plasma cells)
What are major histocompatability complexes?
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)
MHC1
MHC expressed by all nucleated cells that present endogenous peptides (path proteins synth by infected cell) to CD8 +ve cells (cytotoxic T cells)
MHC2
MHC expressed by macrophages, B cells, dendritic cells that present exogenous peptides (synth by pathogen) to CD4 +ve cells (helper T cells)
Why are there different subsets of T helper cells?
-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
