Page 379 - Veterinary Immunology, 10th Edition

Antibody Receptors
VetBooks.ir Lymphocytes receive signals from and hence must have receptors

for antibodies. Since these receptors bind to the Fc regions of
antibody molecules, they are called Fc receptors (FcR). (The
meaning of the term Fc can be found in Chapter 15.) The Fc

receptors for immunoglobulin G (IgG) are designated FcγR since
they bind the γ chain of IgG. Likewise, those for IgA are designated
FcαR and those for IgE are FcεR. Receptors for IgM have been
identified on both B and T cells but are not well characterized.
Four different IgG receptors have been described on mouse

leukocytes (Table 13.4). They are called FcγRI (CD64), FcγRII
(CD32), FcγRIII (CD16), and FcγRIV. All are multichain
glycoproteins. One chain usually binds the antibody, whereas the

other chains are used for signal transduction. CD64 (FcγRI) is found
on dendritic cells, monocytes, and macrophages and to a much
lesser extent on neutrophils. (It is not found on lymphocytes but is
mentioned here for the sake of completeness.) CD64 binds IgG with
high affinity.

TABLE 13.4

Receptors for Immunoglobulin G (FcγR)

Property FcγRI FcγRII FcγRIII FcγRIV
CD CD64 CD32 CD16
designation
Molecular 75 kDa 39-48 kDa 50-65 kDa
weight
Cells Monocytes, B cells, macrophages NK cells, granulocytes, Neutrophils, macrophages,
macrophages granulocytes eosinophils macrophages dendritic cells
Affinity High Moderate Low Intermediate/high
Function Phagocytosis B cells: inhibition NK cells: cytotoxicity Proinflammatory
Macrophages: phagocytosis Granulocytes:
phagocytosis

CD32 (FcγRII) is found on B cells, dendritic cells, and myeloid
cells. It has a moderate affinity for IgG and will therefore only bind
immune complexes (antibody molecules attached to an antigen).
There are three subtypes of CD32 called a, b, and c. CD32a is

expressed on macrophages and neutrophils, where it is an
activating receptor. It promotes phagocytosis and stimulates the
release of cytokines. CD32b is found on B cells, where it is an
inhibitory receptor and regulates antibody production. The function

of CD32c is unclear. All three subtypes are expressed on dendritic

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