1.3 ANTIBODIES, ANTIGEN-ANTIBODY REACTIONS AND IMMUNIZATION

IgG

• most abundant (~75%)

• crosses the placenta  

• neutralizes toxins/viruses

• helps activate the complement system

• marks past infection or vaccination

IgA

• found in saliva, tears, colostrum, and mucus

• protects mucosal surfaces (first line of defense)

• passive immunity via breast milk

IgM

• largest antibody

• first one produced in a new infection

• a (reliable) marker of acute or recent infection

IgE

• binds receptors on mast cells and basophils

• triggers histamine release in allergic reactions

• defends against parasites (parasitic worms)

IgD

• found in minute amounts on immature B cells

• helps initiate B-cell activation

Agglutination

• antibodies bind antigens on the surface of cells or particles

• clumping of cells/particles (used in blood typing)

Precipitation

soluble antigens combine with antibodies to form large, insoluble complexes that are easier for immune cells to clear

Neutralization

• antibodies block a toxin or virus from entering cells

Lysis

the complement system ruptures the pathogen's membrane

Opsonization

• antibodies coat pathogens, making phagocytosis easier (mas visible na siya)

Immunization

stimulates the immune system to recognize and fight a pathogen, either naturally (through infection) or artificially (through vaccines).

Vaccine

introduces a weakened or inactivated antigen, prompting the body to build antibodies and memory cells without causing the disease itself.