Chapter 8: Effector Mechanisms of Humoral Immunity

The Elimination of Extracellular Microbes & Toxins

Properties of Ab Determine Their Effector Functions

• Antibodies may function distant from their site of production

• Protective antibodies are produced during primary response to a microbe and in larger amount during secondary responses

• Antibodies use their Fab regions to bind to and block the harmful effects of microbes & toxins, and they use their Fc region to activate the diverse effector mechanisms that eliminate the microbe

• Isotype switching & affinity maturation enhance the protective functions of antibodies

The Effector Functions of Antibodies

The Effector Functions of Immunoglobins

FcRn lengthens IgG half-life in serum

Antibodies and Fc-containing fusion proteins

Neutralization of Microbes and Toxins by Antibodies

Neutralization of Microbes by Antibodies

Neutralization of Toxins by Antibodies

von Behring and Kitasato experiment (1892)

→ protective substances appeared in serum

→ immunity could be passively acquired

Antibody-Mediated Opsonization and Phagocytosis of Microbes

Cell Distribution and Functions of Fc Receptors

Antibody-Dependent Cellular Cytotoxicity (ADCC)

IgE/eosinophil helminth killing

Early Steps of Complement Activation

Alternative Pathway Proteins

Classical and Lectin Pathway Proteins

Late Stages

Late Stage Proteins

C’ Functions

Regulation of C’

Proteins that Regulate C’

Distribution of various immunoglobins

Transport of IgA Through Epithelium

Evasion of Humoral Immunity by Microbes

Vaccination strategies