Localisation of the monocyte-binding region on human immunoglobulin G

Earlier studies, which provided indirect evidence for the involvement of the Cγ2 domain of human immunoglobulin G (IgG) in human immunoglobulin G (IgG) in human monocyte binding, have been extended to further localise the site of interaction on human IgG. A number of IgGs from several different species and fragments of human IgGs were assayed for ability to inhibit the interaction of radio-labelled human IgG and the human monocyte. By comparison of the amino-acid sequences of those IgGs found to exhibit relatively tight, intermediate or weak binding to human monocyte Fc receptors we are able to postulate a possible monocyte-binding site on human IgG. In addition, the results have implications for the applicability of monoclonal antibodies and antisera when used in the presence of human monocytes and possibly macrophages.