Direct demonstration of immunoglobulin kappa chain RNA in thymus T cells by in situ hybridization.

Mouse thymuses with more than 99% T cells have been reported to contain immunoglobulin kappa mRNA-like molecules (kappa RNA) in relatively large quantities. The present study was undertaken to rule out the possibility that the kappa RNA was mainly a product of a few contaminating B cells of the thymus and to determine whether all T-cell subpopulations contained kappa RNA. By in situ hybridization with DNA complementary to kappa mRNA (kappa cDNA) the following observations were made: 98.5% of thymus cell preparations hybridized with kappa cDNA; the 1.5% unlabeled cells were generally larger and paler staining than the majority of thymus cells. Only 0.015% of thymus cells were intensely labeled and appeared to be plasma cells. Also, 87% of spleen cells hybridized with kappa cDNA; most of these showed similar labeling intensity to the majority of thymus cells. The number of unlabeled cells corresponded to the percentage of hemopoietic cells and macrophages in the spleen. Spleen cells in the range of 0.37-0.85% were intensely labeled and appeared to be plasma cells. The following controls supported the conclusion that the results with thymus and spleen were due to specific hybridization: most of the kappa mRNA-deficient tissue culture cells of the plasmocytoid tumor ABPL-4 did not hybridize with kappa cDNA. The kappa mRNA-producing cells from myeloma PC 3741 hybridized in situ with kappa cDNA. Furthermore, all cells from this tumor and all spleen cells hybridized uniformly with a cDNA probe complementary to most of the total cellular poly(A)-containing RNA species of these cells. These results indicate that T cells of all types in the thymus as well as in the periphery contain substantial quantities of kappa RNA.