C4 antibody mediated immunity Flashcards
antibody specificity and production
produced by b lymphocytes
can only attach to their specific antigen
pathogen can be recognised by multiple antibodies- each type is specific to a diff antigen of the pathogen (surface/internal/excreted)
how can antibodies mediate in a number of responses
interact with complement
-cell lysis/attach innate cell
ineract with phagocytic cells (via fc portion of anti b)
can have neutralising effect-eg block viral entry into cell
what enhances rate of phagocytosis
if the target is opsonised (increases >4000x)
neutralisation of a toxin by an antibody
-toxin binds to cellular receptors
-endocytosis of toxin:receptor complexes
-dissociation of toxin releases its active chain which poisons cell
-antibody protects cell by blocking binding of toxin
how antibodies can mediate in killling by NK cells
-antibody binds antigens on surface of target cells
-Fc receptors on NK cells recognise bound antibody
-cross linking of Fc receptors signals the NK cell to kill target cell
-target cell dies by apoptosis
where is most IgA present
gut, produce 50mg/kg/day
what occurs in IgA deficiency and symptoms
recurrent bacterial, enteroviral or protozoal infections of the respiratory and GI tract
is asymptomatic because IgM exerts compensatory function
what is IgA important for
important in defense against intestinal pathogens (rotavirus)
present in genital-urinary tract secretions can protect against HIV- neutralise viral particles
IgG importantance and abundance where
is the main Ig class produced during immune response
>75% of total circulating Igs in the blood
how does IgG mediate phagocytosis
by macrophages/neutrophils- opsonin induces enhanced endosomal maturation and efficient degradation of lysosomal contents
how does IgG mediate antibody dependent cellular cytotoxity
by NK cells- FcyRIIIa-cross-linking on NK cells triggers activation and release of perforin and granzymes- induces apoptosis of infected/abnormal cells
how does IgG mediate degranulation of neutrophils, eosinophils and mast cells
when FcyRs croos-linking triggers rapid degranulation-generation and release of reactive oxygen (ROS) and reactive nitrogen species (RNS)-potent bactericidal effects
what 3 things do IgG mediate
- phagocytosis by macrophages/neutrophils
- antibody dependent cellular cytotoxicity by NK cells
- degranulation of neutrophils, eosinophils and mast cells
where is IgM the first Ig to appear in and where is it present
first Ig isotype to appear during phylogeny, ontogeny, and host immune responses
present in new born babies (natural IgM
produced in response to antigenic stimulation of B cells - adapive IgM
what can IgM antibodies recognise
a wide range of different microbial components- viral antigens and bacterial toxins
high avidity of polymeric IgM
meaning it can immobilise target at a site-stop bacteria spreading
