Topic 17 Immune Functions Of Antibody

Appropriately match each Fc receptor in the following list with its primary function:FcR1, FcRI, FcRII-A, FcRII-B1, FcRII-B2, FcRIII, and FcRI. (function should be either opsonization, inhibitory, granule exocytosis, or ADCC)

FCaR1: Opsinization FCYR1, FCYR2A, FCYR3: ADCC Fc-gamma RII-B1, Fc-gamma RII-B2: Inhibition Fc-epsilon RI: Granule Exocytosis

Describe the important function(s) of FcRn(Brambell receptor) in bothpre-and post-natal human

FcRn receptor binds to IgG and the FC region within endocytic vesicels of capillary endothelium. They transport IgG across endothelial cell constitutively into extracellular spaces, this happens in the absence of inflammation. Also this is the mechanism used for passive immunity for newborn.

Identify the two forms of passive antibody immunity that a fetus/newborn receives from its mother

IgG, and Dimeric IgA. The IGA is concentrated in breast milk and protects from gut bacteria.

Identify the 3 major antibody isotype(s) in body fluids and specifically indicate whether each isotype is confined to the bloodstream or can enter tissue fluids.

IgM =Mostly in blood; low affinity in tissue IgG=Connective tissue/insterstitial fluid, placenta/passive immunity IgA=Tissue/blood and mucosal Note: IgG and IGA are able to enter tissue fluid

Describe the activation of the classical complement pathway from IgM to the C3 convertase, identifying the complement proteins involved and the proper order of cleavage and binding.

IgM binds antigen causing a conformational change in structure allowing for C1 as well as R and S enzymes to bind to initiate the procedure.

Describe how IgA produced in mucosal lamina propria can get across the mucosal epithelial layer to be released in high concentration into mucus

Iga from Basolateral portion is transported via receptor mediated endocytosis and goes through mucous through secretory piece.

Identify the protein that is necessary to produce IgA as a dimer.

J chain

Define and provide examples ofthe major functions of antibody (including ne utralization, opsonization, complement fixation, and ADCC).

Neutralization: Destroy toxins and prevent the binding of pathogens to body, e.g: High affinity IgG and IgA can block exotoxin and venom binding to receptors, receptors can be coated also to prevent viral infection Opsinization: Targets phagocytosis; e.g: Macrophages and neutrophils Complement Fixation: Classical pathway; lysis of bacteria, phagocytosis by myeloid lineage cells via CR. Clearance of immune complexes by CR1 on RBC ADCC: Relies upon FCR interaction with antibody on pathogen, to drink killing of infected cell with NK cells

Describe the relative order and time of appreciable appearance(30- 50% of adult levels)of IgA, IgG, and IgM in the bloodstream during newborn early childhoodyears, for antibody produced by the child itself (not from mother)

Passive IgG peaks at birth Next IGM followed by IgG and IGA

Define the following terms [including what cell(s) the term applies to, as appropriate]:Passive immunity (i.e. passive antibody), "fix complement", poly -Ig receptor, J-chain, secretory component, Fc, and FcR.

Passive Immunity: Transfer of antibodies from one to another Fix complement: Induced classical pathway via Igm binding of antigen on surface of pathogen Poly-Ig Receptor: Binds Dimeric IgA on basolateral surface of mucosal cell and transports to apical surface with component of Polg Ig receptor J-Chain: Joins identical IgA together and Ig receptor Secretory component: Cleaved off portion of Poly IG that travels to apical surface with IGA dimer FCRS: Located on phagocytes that bind to opsinized pathogens (coated with antibody, some are inhibitory and limit inflammation, some trigger granule exocytosis of mast cells, basophils and eosinophils, can induce killing infected cells by Nk cells-Antibody dependent cytotoxicity

Describe the role of RBC in removing immune complexes from the plasma

The C3b coating attaches to the CR1 receptor of the RBC and the RBC brings a pathogen to the spleen where the macrophages also contain the complement receptor and the pathogen is opsonized.