HUMORAL HUMORAL IMMUNITYIMMUNITY

Fe A. Bartolome, MD, FPASMAPFe A. Bartolome, MD, FPASMAPDepartment of MicrobiologyDepartment of MicrobiologyOur Lady of Fatima UniversityOur Lady of Fatima University

HUMORAL IMMUNITYHUMORAL IMMUNITY

Antibody mediated Part of Specific immunity along

with cell-mediated type When Nonspecific immunity fails,

tissue macrophages take up the organisms

specific immune responses activated

Antibody is synthesized

HUMORAL IMMUNITY

Primary molecular component: antibody

Ab is made by B-cells and plasma cells in response to Ag challenge

Ab: protection vs re-challenge block spread of agent in blood facilitate elimination of

infectious agent

HUMORAL IMMUNITY

Ab must also interact with host cells (macrophage, complement)

Ab also serve as B-cell receptors to stimulate plasma cell growth and produce more Abs

HUMORAL IMMUNITY

Antimicrobial Action of Antibodies:

1. Opsonic; promote ingestion and killing by phagocytic cells

2. Neutralize (block attachment) toxins and viruses

3. Agglutinate bacteria; may aid in clearing

4. Render motile organisms non-motile

HUMORAL IMMUNITY

Antimicrobial Action of Antibodies:5. Combine with Ags on the microbial

surface activate complement cascade induce an inflammatory response bring fresh phagocytes and serum Abs into the site

6. Combine with Ags on the microbial surface, activate complement cascade, anchor the membrane attack complex (C5b to C9)

HUMORAL IMMUNITY

Immunoglobulins (Antibodies)1. IgD• Exists primarily as

membrane/surface IgD on B-cell, along with IgM they are the only isotypes expressed by the same cell

• no known biologic function• less than 1% of serum Igs• 185 kDa molecular mass

HUMORAL IMMUNITY

Immunoglobulins (Antibodies)2. IgM• first Ab produced versus Ag

challenge• can be produced in T-

independent manner• 5-10% of total Igs in the adult• half life 5 days• pentameric: 5 units joined by

disulfide bonds and the J chain (900 kDa)

HUMORAL IMMUNITY

Immunoglobulins (Antibodies)2. IgM• theoretically has 10 Ag binding

sites;• binds complement the best (1

pentamer activates the classic pathway)

• Monomeric IgM is with IgD on surface of B cells

• cannot go from blood to tissue because of size

HUMORAL IMMUNITY

Immunoglobulins (Antibodies)3. IgG• about 85% of all Igs in the

adult• half life of 23 days (longest)• molecular mass of 184 kDa• 2 L chains of 22,000 Da and 2 H

chains of 55,000 Da each• 4 subclasses: IgG 1-4, diff

structure, relative concentration and function

HUMORAL IMMUNITY

Immuneglobulins (Antibodies)3. IgG• production is T-cell

dependent; can cross the placenta

• principal Ig in booster and anamnestic response

• high binding capacity for Ags, fixes complement, stimulates chemotaxis and acts as opsonin

HUMORAL IMMUNITY

Immunoglobulins (Antibodies)4. IgA• 5-15% of all Igs in the adult• half life of 6 days• molecular mass of 160 kDa,

basic 4-chain monomer, but can occur as dimers, trimers or multimers thru the J chain

• Secretory IgA = appears in body secretions for local immunity

HUMORAL IMMUNITY

Immunoglobulins (Antibodies)4. IgA

• production requires T-cell help and mucosal stimulation by adjuvants like cholera toxin and attenuated salmonella

• binds to poly-Ig receptors on epithelial cells for transport across cells

HUMORAL IMMUNITY

Immunoglobulins (Antibodies)4. IgA

• about 2 gms of IgA/day secreted by adults

• appears in colostrum, intestinal and respiratory secretions, saliva, tears and other secretions

• IgA-deficient persons have more frequent respiratory tract infections

HUMORAL IMMUNITY

Immunoglobulins (Antibodies)5. IgE

• less than 1% of total serum Igs in adults

• half life of about 2.5 days• most are bound to Fc receptors on

mast cells and serve as receptors for allergens and parasite Ags

• once IgE is bound by Ag, mast cells release histamine, prostaglandin, platelet activating factors and cytokines

HUMORAL IMMUNITY

Immuneglobulins (Antibodies)5. IgE

• serve as protection versus parasitic infections

• responsible for the manifestations of anaphylactic (Type 1) hypersensitivity