10. antibody effector functions (+ monoclonal antibodies)

general effector functions of antibodies

• neutralization of microbe and toxins

• opsonization and phagocytosis of microbes

• antibody-dependent cellular cytotoxicity

• complement activation

effector functions are activated after _____

antibodies bind antigens; antigen-dependent

how does neutralization work?

• antibodies coat microbes/toxins and prevent attachment to host cells

• also helps to localize infection and prevent spread to other cells

sterilizing immunity

preventing infection

Fab

sufficient to neutralize the infectivity of microbe/harmful effects of toxin

Fc portion

utilized by antibodies to eliminate neutralized microbes

antibody-dependent cellular cytotoxicity (ADCC)

killing of antibody-coated cells by natural killer cells

functions of complement

• opsonization and phagocytosis

• stimulation of inflammatory reactions

• complement-mediated cytolysis

how does agglutination inhibit bacterial infection?

• prevents bacterial colonization

• promotes phagocytosis

• increased clearance by peristalsis (gut) and cilliary movement (respiratory tract)

microbial evasion of humoral immunity

• antigenic variation

• inhibition of complement activation

• conceal antigen under capsule → blocking phagocytosis by hyaluronic acid capsule

regions involved in antigen recognition (antigen receptor molecules)

vary between clones of lymphocytes

regions required for signal transduction (antigen receptor molecules)

relatively conserved

invariant molecules

• function to deliver the activation signal inside of the cell triggered by antigen recognition

• non-covalently attached to antigen receptors

epitope (antigenic determinant)

• portion of antigen that binds the antigen receptor

• 5-22 amino acids for a protein epitope

**note: one antigen may have multiple epitopes

multideterminant antigen

antigens have many different epitopes on the same molecule → polyvalent

continuous/linear epitope

single polypeptide segment (amino acids are adjacent in sequence)

conformational/discontinuous epitope

amino acids from different parts of the sequence brought together by protein folding

polyclonal

production of multiple clones of B cells directed against a multifaceted antigen (e.g. serum post recovery)

monoclonal

production of a single clone B cell against a single facet of the antigen (made in laboratory)

passive immunity

antibody given

active immunity

antibody made in response to antigen