The Immune System

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on surface of

B cells that have

not been exposed

to antigens

Acts as antigen

receptor in the

antigen-stimulated

proliferation and

differentiation of

B cells (clonal

selection)

Most abundant Ig

class in blood;

also present in

tissue fluids

Promotes opsoniza-

tion, neutralization,

and cross-linking of

antigens; less effec-

tive in activation of

complement system

than IgM

Provides localized

defense of mucous

membranes by

cross-linking and

neutralization of

antigens

Presence in breast

milk confers

passive immunity

on nursing infant

Present in blood

at low concen-

trations

Slide 52

Distribution

Class of Immuno-

globulin (Antibody)

IgM

(pentamer)

J chain

First Ig class

produced after

initial exposure to

antigen; then its

concentration in

the blood declines

Promotes neutraliza-

tion and cross-

linking of antigens;

very effective in

complement system

activation

Function

Slide 53

Distribution

Function

Class of Immuno-

globulin (Antibody)

IgG

(monomer)

Most abundant Ig

class in blood;

also present in

tissue fluids

Promotes opsoniza-

tion, neutralization,

and cross-linking of

antigens; less effec-

tive in activation of

complement system

than IgM

Only Ig class that

crosses placenta,

thus conferring

passive immunity

on fetus

Slide 54

Distribution

Function

Class of Immuno-

globulin (Antibody)

IgA

(dimer)

J chain

Secretory

component

Present in

secretions such

as tears, saliva,

mucus, and

breast milk

Provides localized

defense of mucous

membranes by

cross-linking and

neutralization of

antigens

Presence in breast

milk confers

passive immunity

on nursing infant

Slide 55

Distribution

Function

Class of Immuno-

globulin (Antibody)

IgE

(monomer)

Present in blood

at low concen-

trations

Triggers release from

mast cells and

basophils of hista-

mine and other

chemicals that cause

allergic reactions

Slide 56

Distribution

Function

Class of Immuno-

globulin (Antibody)

IgD

(monomer)

Trans-

membrane

region

Present primarily

on surface of

B cells that have

not been exposed

to antigens

Acts as antigen

receptor in the