Notes 4.24a

I. Classes of antibody = isotypes
-different isotype properties because of different heavy chains
-different Fc regions
a) IgG
-most common isotype of antibody found in the blood
-binds very avidly to antigens (more so than other types)
-most often associated as an opsonin
-“free antibody”—not attached to the surface of the cell
-transported across the placenta from the mother’s blood
*passive immunity: “acquired immunity to pathogen from pre-formed
antibody from someone else
b) IgM
-forms pentamers
-doesn’t bind as avidly as IgG individually (but binding sites work t
together in pentamer to increase binding avidity)
-as a flat molecule, IgM pentamer not bound by C1
-but when bound to microbe, making “tent”, allows C1 bind
-first isotype of antibody to be secreted by B-cell
-IgM bound to B-cell surface = receptor part of B-cell receptor
c) IgE
-mast cell (granules hold inflammatory mediators-histamine), eosinophil
degranulation (granules contain antimicrobial peptides)
-histaminebronchoconstriction, mucus secretion
II. Immunopathology: Types of Hypersensitivity reactions
a) Type I
-IgE against wrong target (x: allergies, asthma)
Hygiene Hypothesis: Allergies occurrence in "clean" environments because we aren't exposed to enough large parasites (i.e. tapeworms)
b) Type II
c) Type III
d) Type IV
i. The PPD test, and why we don’t vaccinate for tuberculosis in the USA

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