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

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Abstract
Mouse thymuses with more than 99% T cells have been reported to contain immunoglobulin κ mRNA-like molecules (κ RNA) in relatively large quantities. The present study was undertaken to rule out the possibility that the κ RNA was mainly a product of a few contaminating B cells of the thymus and to determine whether all T-cell subpopulations contained κ RNA. By in situ hybridization with DNA complementary to κ mRNA (κ cDNA) the following observations were made: 98.5% of thymus cell preparations hybridized with κ 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 κ 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 κ mRNA-deficient tissue culture cells of the plasmocytoid tumor ABPL-4 did not hybridize with κ cDNA. The κ mRNA-producing cells from myeloma PC 3741 hybridized in situ with κ 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 κ RNA.