Association between Immunoglobulin and Macrophages in Primary Methylcholanthrene-induced Sarcomas¹

Ten primary 3-methylcholanthrene-induced murine sarcomas ranging in size from 0.37 to 3.22 ml were selected for studies of tumor-associated immunoglobulin. The purpose of these particular studies was to determine if a significant proportion of the immunoglobulin was bound to receptors for the Fc portion of Immunoglobulin G molecules on tumor-associated host lymphoreticular cells. The distribution of tumor-associated immunoglobulin was compared to the distribution of macrophages within the tumors using indirect immunofluorescence with specific antisera. Significant amounts of λG₁, λG_2a, λG_2b, and λG₃, lesser amounts of λA, and very little λM were observed. The distribution of each class of immunoglobulin within the tumor was essentially the same, and distribution paralleled the distribution of the tumor-associated macrophages detected with specific antimacrophage serum. Double-labeling studies using fluorescein and rhodamine isothiocyanate-conjugated reagents confirmed that the majority of the immunoglobulin was bound to the same cells that were reactive with the antimacrophage serum. Furthermore, most of the tumor-associated immunoglobulin, regardless of class, was eluted by washing tissue sections for 5 hr at 37°, a procedure which effectively removes immunoglobulin bound to cellular Fc receptors. B-lymphocytes or plasma cells were rare in the tumors. Those observations provide strong suggestive evidence that most tumor-associated immunoglobulin in primary murine sarcomas is bound to receptors for the Fc portion of Immunoglobulin G molecules on macrophages, possibly in the form of antigen-antibody complexes.