Expression of T cell antigen receptor and immunoglobulin genes in lymphoid organs visualized by in situ hybridization.

In situ hybridization techniques were used to detect expression within lymphoid tissues of genes encoding T cell receptor (TCR) alpha, beta and gamma chains, as well as immunoglobulin kappa light chain. Transcripts of these genes were specifically detected in frozen sections of thymus, spleen and lymph node but not in non-lymphoid tissues. Differences in the level of beta chain gene transcription were observed within and between the thymus cortex and medulla, with approximately 60% and 34% of cells in these areas labelled, respectively. Expression of the TCR alpha chain genes was more homogeneous, while amongst the cells transcribing the gamma chain gene, there was a subpopulation of 0.2% of heavily labelled cortical thymocytes. Labelling of T cell dependent areas of spleen and lymph nodes was observed with each of the TCR probes, but neither alpha nor beta gene expression was seen in lymphoid tissues of athymic nude mice. The gamma chain gene was, however, expressed in both spleen and lymph nodes of these mice. These results indicate that TCR gene expression is not limited to a small subpopulation of T cell precursors. They are discussed in relation to T cell differentiation within the thymus.