DIAL 3. Effector Mechanisms of Antibody-Mediated Immunity

Question 1

Identify the antibody isotypes involved in neutralization, opsonization, and complement activation and the general role of the these processes in antibody mediated immunity

Answer 1

neutralization - mediated by neutralizing antibodies (NAb), bind to microbe to prevent passing through membranes, and inactivation of pathogenic ligands, also block the binding of toxins to cell receptors

Opsonization - mediated by IgG (IgE maybe), promotes microbe ingestion by phagocytes, also cause ADCC (by NK cells & defense against helminthic parasites

Complement - IgM or some IgG, opsonizes for phagocytes, form MAC, and bind to neutrophils to release inflammatory peptides

Question 2

Describe the characteristics and functions of Fc receptors involved in antibody-mediated phagocytosis and in antibody-mediated defense against helminthic parasites

Answer 2

Ab-mediated phagocytosis - FcGR1 on macrophages and neutrophils activate the cell when bound to Fc portion of IgG, major defense against encapsulated bacteria

Ab-mediated Helminthic defense - Plasma cells switch to producing IgE for eosinophils and mast cells with FcERI to dump granule contents on parasite

Question 3

Compare and Contrast the early steps and outcomes of complement activation by the classical, alternative, and lectin pathways

Answer 3

Alternative - activated by microbes without regulatory proteins to stop binding of C3b

Classical - IgM or IgG bind to microbe and activate complement peptides

Lectin - activated when MBL binds to microbe

All pathways result in formation of Membrane Attack Complex (MAC) in late stage and release of inflammatory peptides and opsonization by C3b

Question 4

Explain the general mechanism by which complement activation promotes opsonization inflammation, and microbe lysis.

Answer 4

Opsonization - microbes coated with C3b are phagocytosed (C3b is recognized by CRI)

Inflammation - C5a, C4a, C3a are release as cleaved peptides and are chemotactic for neutrophils to release inflammatory proteins

Microbe lysis - C5b starts formation of MAC. C6, C7, C8, C9 subsequently bind.

Question 5

Describe the general mechanism that prevent complement-mediated damage to host cells

Answer 5

Mammalian cells express regulatory proteins that interfere with the cleavage and binding of complement peptides.