There are five types antibodies secreted
by B cells in the human body.  These
have initials as names: M, A, D,
G and E. Don't forget we call them Ig.  IgM is a pentamer, meaning it's got  five
antibodies sticking out of the middle.
It's an early response shock troop
of what we call "humoral immunity."
These are secreted before the mature
response is complete.
IgA is a dimer.  It lines the gut, the respiratory tract and the urogenital
tract to prevent colonization.
IgD is found on naive B cells.
IgG is the big kahuna.  It is the major
defender against invading
pathogens.  It also crosses the placenta and
protects the fetus.
IgA is secreted in breast milk, so
together,
these two antibodies confer fetal and
neonatal immunity.
IgE binds to allergens and parasitic
worms, 
and it causes mast cells and basophils to
release histamine, which causes allergy symptoms.
