Partial characterization of different cell types found in the Xenopus laevis lymphoreticular tumor based on the presence or absence of surface immunoglobulins and Fc molecules.

Cells of Xenopus laevis lymphoreticular tumor induced by tumor tissue transplantation were examined for surface Ig and Fc receptor molecules in order to evaluate the different cell types found in the tumor. Direct immunofluorescent technique, using fluorochrome conjugated rabbit antisera to Xenopus Ig's, detected Ig molecules on the surface of a mean of 31.7 +/- 11.3% of cells in tumor suspensions. Most of these molecules were of IgM isotype, reversibly bound to the cell membrane (cytophilic) and could be dissociated by acid pH or overnight cell culturing. In addition integral membrane IgM was detected on the surface of 10.2 +/- 5.9% of the cells. The serum origin of cytophilic Ig's and the cellular origin of integral membrane Ig's were confirmed by analysis of electrophoretic mobility of their heavy chains on SDS-polyacrylamide gels. The existence of Fc receptor molecules on the surface of 48.6 +/- 16.6% of the cells was demonstrated by fluorescent staining using heat aggregated FITC labelled IgM or FITC or TRITC labelled antigen-complexed IgY antibodies. 32.2 +/- 12.4% and 16.4 +/- 6.8% of the cells bore receptors for IgY or receptors for IgM respectively, while 6.3 +/- 3.1% carried receptors for both Ig's. Double fluorescent staining revealed that 28.9 +/- 4.5% of cells bearing IgM on their surface expressed also receptors for IgY. These results attest to the heterogeneity of the tumor cell population, in respect to the presence or absence of FcR-IgY, FcR-IgM, sIgM, and cytophilic IgM surface molecules.