Distinct differences in the capacity of monocyte FcγRII of different individuals to bin or not bind mouse IgG1 defines a polymorphism of FcγRIIa and has previously been defined as the high responder (HR) or low responder (LR) polymorphism of FcγRII. The precise definition of the molecular basis of the human HR/LR polymorphism of FcγRIIa from the peripheral blood mononuclear cells of normal individuals has been determined by anti‐CD3 induction of T cell proliferation, the polymerase chain reaction (PCR), nucleotide sequencing, transfection and IgG binding. Amplification of first strand cDNA from mRNA isolated from mononuclear cells was performed by PCR using primers specific for the sequences encoding the leader and cytoplasm sequences of FcγRIIa, which is normally expressed in monocytes. Sequencing of the PCR products and transfection of these to FcγR cells indicated that in FcγRIIa of HR or LR individuals; (i) three nucleotide substitutions (CA to TG and G to A) resulted in the change of glutamine to tryptophan at position 27 (first extracellular domain) and arginine to histidine at position 131 (second extracellular domain); (ii) expression of cDNA encoding the various combinations of these indicated that arginine at position 131 was essential for IgG1 binding whereas the amino acid changes at position 27 had no effect; and (iii) IgGf at high concentration bound to all allomorphic forms of FcγRIIa. These results indicate that position 131 in the second extracellular domain of FcγRIIa is intimately involved in immunoglobulin binding. Furthermore, the apparent inability of IgG1 to bind to FcγRIIa of non‐responder individuals is not absolute in that immune complexes sensitized with a high concentration of MIgG1 will bind to non‐responder‐type FcγRIIa.
|Number of pages||9|
|Journal||Immunology and Cell Biology|
|Publication status||Published - 1 Jan 1992|