BIOL 1103 Lecture Notes - Mast Cell, Complement System, Immunoglobulin M

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30 Jan 2013
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Outline of Lecture 05
Effector Functions of Antibody
Remember: Ab effector functions are mediated by the heavy chain constant region (Fc)!!!
I. Transport across mucous membranes
A. Mucosal surfaces (e.g. GI and respiratory tract) present special immunologic
challenges
B. The mucosal immune system is essentially independent from systemic
immune system
C. IgA is used:
1) Prevents attachment of pathogens to mucosa
2) Is a barrier to environmental antigens (hence prevents allergies)
3) Most abundantly secreted Ig (3g/day into intestines!)
4) Is a dimer held together by J chain
D. Secretory component
Produced by epithelia, acts as IgA receptor, transcytoses it
SC1 domain non-covalently interacts with IgA/J, SC5 covalently links to
Cα2
Prevents proteolysis of IgA by self and pathogens
E. Across placenta: IgG is actively transported across placenta to fetus via Fc
receptors
II. Non-Inflammatory Activities
A. Review of influenza virus
HA and NA coat glycoproteins are responsible for attachment and
infection
Viral strains can be distinguished by antigenically different HA and NA
B. Mechanisms of neutralization by Ab
1) Inhibit binding of virus to target cells (sterically block NA)
2) Inhibit virus from entering cell
3) Inhibit endocytic vessel fusion necessary for infection
III. Inflammatory Activities (4 items)
1) Opsonization
Mediated by IgG and neutrophils/macrophages
Ag binds bacteria; Fc receptors by Ab; particle is phagocytosed in zipper
fashion
2) Complement
IgM or crosslinked IgG activate C1q, which starts complement cascade
Complement forms a porin in bacterial cell wall causing lysis
C3b enhances opsonization
3) Activation of mast cells
Mediated by IgE bound to Fc receptors on mast cells
Crosslinking IgE causes degranulation and phospholipase A2 activation
Results in inflammatory response (e.g. against parasites or allergens)
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