Phagocytic Cell Fc Receptors

Following interactions with the endothelium, the neutrophils express a number of specific receptors including Fc receptors for immunoglobulins (Table 1). Three classes of receptors are expressed by phagocytic cells: FcyRI (CD64), FcyRI (CD32), and FcyRIII (CD16). Most receptors are hetero-oligomeric complexes consisting of nine membrane-associated FcRs and three soluble FcryRs coded by eight genes. The receptors are transmembrane proteins with similarities to the BCR and TCR recognition proteins. Some receptors have "immu-noglobulin-like" domains. High-affinity FcyRI (CD64) contains three immu-

Tablet Cellular Receptors on the Surface ofPhagocytic Cells




CR1 (CD35)

Activated PMNs

C3b, iC3b, and C4

Follicular dendritic cells

CR2 (CD21)

Follicular dendritic cells

iC3b and C3dg

CR3, Mac-1, CDllb/CD18



Activated PMNs

Dendritic cells

FC7RI (CD64)


Human IgGl and IgG3

Activated PMNs

Mouse IgG2a

Oxidative burst

Fc^RII (CD32)


Polymeric IgG

Activated PMNs

Respiratory burst



IgG2a and IgG3

noglobulin-like domains in the extracellular region. FcyRII and FcyRIII have only two immunoglobulin domains and a lower binding affinity for IgG (Deo et al., 1997).

Genetic polymorphism among the Fc receptors is common. Alternate forms ofFcyRII (CD32) differby a single amino acid (arginine or histidine) at position 131 in the second Ig domain creating FcyRIIa-R131 or FcyRIa-H131(Fig. 1). The low-affinity receptor FcyRIIIalso has two alternate forms: FcryRIIIa and FcyRIIIb. Subtypes of both the FcyRIIIa and b receptors have been identified. The two allotypes of FcyRIIIa contain either valine or phenylalanine at position 158. Allotypes of FcyRIIIb-NAl or NA2 differ in five nucleotides that result in different glycosylation patterns (Deo et al., 1997)

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