Chapter 12 Flashcards
Humoral immunity is mediated by antibodies and
is the effector arm of the adaptive immune system
responsible for what?
defense against extracellular
microbes and microbial toxins. The antibodies that
provide protection against infection may be produced by long-lived antibody-secreting cells generated by the first exposure to microbial antigen
or by reactivation of memory B cells by the
antigen
The effector functions of antibodies include?
neutralization of antigens, Fc receptor–dependent
phagocytosis of opsonized particles, and activation
of the complement system.
Antibodies block, or neutralize, the infectivity of
microbes by what?
binding to the microbes and sterically
hindering interactions of the microbes with cellular receptors. Antibodies similarly block the
pathologic actions of toxins by preventing binding
of the toxins to host cells.
Antibody-coated (opsonized) particles are phagocytosed how?
by binding of the Fc portions of the antibodies to phagocyte Fc receptors. There are several
types of Fc receptors specific for different
subclasses of IgG and for IgA and IgE antibodies,
and different Fc receptors bind the antibodies
with varying affinities. Attachment of antigencomplexed Ig to phagocyte Fc receptors also delivers signals that stimulate the microbicidal activities
of phagocytes
The complement system consists of what?
serum and
membrane proteins that interact in a highly regulated manner to produce biologically active protein
products
The three major pathways of complement activation are what?
the alternative pathway, which
is activated on microbial surfaces in the absence of
antibody; the classical pathway, which is activated
by antigen-antibody complexes; and the lectin
pathway, initiated by collectins binding to antigens
pathways generate enzymes that
cleave the C3 protein, and cleaved products of C3
become what?
covalently attached to microbial surfaces or antibodies, so subsequent steps of complement
activation are limited to these sites
All pathways
converge on a common pathway that involves what?
the
formation of a membrane pore after the proteolytic cleavage of C5.
Complement activation is regulated by what?
various
plasma and cell membrane proteins that inhibit
different steps in the cascades.
The biologic functions of the complement system
include what?
opsonization of organisms and immune
complexes by proteolytic fragments of C3, followed by binding to phagocyte receptors for complement fragments and phagocytic clearance,
activation of inflammatory cells by proteolytic
fragments of complement proteins called anaphylatoxins (C3a, C4a, C5a), cytolysis mediated by
MAC formation on cell surfaces, solubilization and
clearance of immune complexes, and enhancement of humoral immune responses.
Protective immunity in neonates is a form of what?
passive immunity provided by maternal antibodies
transported across the placenta by a specialized
neonatal Fc receptor
