Classes of Immunoglobulins

5-6 days

serum half-life of IgM

IgM

first Ig to be produced in an immune response

IgM

effective in agglutination & cytolytic reaction

IgM, IgG

decreases in primary & secondary Ig deficiencies

IgM

increased in infectious diseases, collagen disorders, hematologic disorders

IgM

1st to appear / increase in primary immune response

IgM

1st to appear in maturing infants

IgM

continuously synthesized as long as Ag is present

IgM

no memory

1. complement fixation

2. agglutination

3. opsonization

4. neutralization of tissues & toxinxls

major functions of IgM

IgM

largest, longest, widest Ig, pentamer & decavalent

10 binding sites

IgM # of binding sites

IgM

“star” or “crab” shaped

IgM

most effective agglutinin that’s why it is aka “clumping antibody”

IgG

major IgG in serum

23 days

IgG serum half life

IgG

can cross the placenta

IgG

provides immunity to the newborn

IgG

involved in agglutination & precipitation

IgG4

only IgG subclass that does not activate complement

IgG3

most effective in activating complement

IgG

smallest & shortest Ab, monomer & divalent

IgG

“Y shaped” Ig

2 binding sites

IgG # of binding sites

intrauterine infection

indication if IgM is seen in serum of babies

IgG

warm Ab

IgM

cold Ab

IgG

protein reacting Ab

IgM

saline reacting Ab

class switching phenomenon

IgM decreases = IgG increases (replace IgM)

conglutinin

Ab that causes clumping with AHG only

IgG

conglutinin

agglutinin

Ab causes immediate clumping

IgM

agglutinin

IgA

predominant Ig in secretions: saliva, tears, colostrum, milk, intestinal fluids

5-6 days

IgA serum half-life

plasma IgA

IgA synthesized by plasma cells

secretory IgA

IgA synthesized by cells of intestinal wall

glycoprotein

“secretory component”

secretory component

• protects IgA from digestion by proteolytic enzymes

• facilitates IgA transport

IgA

dimer, tetravalent

4 binding sites

IgA # of binding sites

secretory IgA

present if fluids & is stabilized against proteolysis

IgE

mediates some type of hypersensitivity reaction (allergy)

IgE

most heat labile

type I hypersensitivity

immediate hypersensitivity wherein binds to receptor of mast cells & basophils + Ag exposure → release of Histamine & Heparin

IgE

least abundant

2-3 days

IgE serum half-life

IgE

elevated in helminthic infections along w/ eosinophils

IgE

monomeric, divalent w/ extended hinge region

2 binding sites

IgE # of binding sites

IgD

extremely susceptible to proteolysis

2-3 days

IgD serum half-life

IgD

increased in autoimmune responses; scleroderma, Hashimoto’s thyroiditis, LE, RA