Binding of aggregated human immunoglobulin to murine thymocytes and T cells through receptors for the Fc region.

Normal thymus lymphocytes and T cells of mice have the ability to bind heat-aggregated IgG of human origin (aggHIgG), as shown by indirect immunofluorescence. At 4 degrees, the cells bind aggHIgG with an irregular speckled appearance; at 37 degrees, the aggregates are incorporated into the surface membrane, inducing rearrangement of the receptors and capping. At the point of maximum binding capacity, thymocytes show a fairly homogeneous fluorescence pattern, whereas T cells show a heterogeneous appearance. Aggregated pure human Fc fragments, but not Fab fragments, retained not only the binding capacity of the complete molecule but also the ability to induce cap formation on the surface of thymusceds, at 37 degrees.