A requirement for native (undenatured) IgG for detection of species specificity of the IgG-Fc receptor on lymphocytes.

The species specificity of the Fc receptor involved in binding of preformed antibody-antigen complexes was examined using complexes of deaggregated 7S antibodies and albumin antigens. Complexes prepared with mouse antibodies bound to 3-4 times as many cells as complexes prepared with rabbit, guinea pig, or goat antibodies. Using lymphocytes from each species, it was shown that homologous complexes consistently labeled a higher frequency of cells than heterologous complexes. The binding of heterologous complexes seemed to be generally restricted to monocytic populations which were also capable of binding monomeric 7S immunoglobulins. It is concluded that the lymphocytic Fc receptor for antigen-complexed 7S immunoglobulin displays strict species specificity. Heat aggregation of the heterologous immunoglobulins eliminated the species restriction on their binding to the lymphocytic Fc receptor. It is therefore suggested that artificially aggregated immunoglobulins may not be reliable probes for the specificity of the Fc receptors.