THYMUS-INDEPENDENT EXPRESSION OF A TRUNCATED T-CELL RECEPTOR-ALPHA MESSENGER-RNA IN MURINE KIDNEY

During studies on gene expression in the kidney, we unexpectedly observed that murine kidney expresses a truncated form of TCR-alpha mRNA (1.3-1.4 kb). This transcript was not associated with the presence of complete TCR-alpha mRNA (1.7 kb) or detectable TCR-beta or -delta transcripts, thus indicating that the truncated TCR-alpha mRNA could not be attributed to blood contamination of the kidney RNA preparation. The truncated TCR-alpha message appeared to contain at least the C-alpha region, as suggested by hybridization with an intra-C-alpha 24 oligonucleotide probe, by amplification of the C-alpha region with the polymerase chain reaction from total kidney mRNA, and by sequencing of, and hybridization with, the amplified products. In situ hybridization of kidney sections indicated that the transcript was expressed in interstitial cells. Northern blots of cortex and medulla RNA showed that the cells expressing the truncated TCR-alpha mRNA were predominantly located in the medulla. To investigate the possibility that the transcript was not produced by T cells or NK cells, fractionation of renal cell suspensions were performed. The truncated TCR-alpha mRNA was detected in a fraction containing large (low buoyant density) cells in which no expression of CD3, Thy 1, or NK-1.1 was detected, indicating that these cells are not mature T cells, do not express a functional TCR, and are not NK cells. The cells expressing the truncated TCR-alpha mRNA were radiosensitive, and were not thymus dependent, because this transcript was as abundant in nude mice as in normal mice. The transcript was not detected in bone marrow. Expression of the truncated TCR-alpha mRNA was not dependent on an intact recombinase activity as its expression was not affected by the severe combined immunodeficiency mutation. Our results show that murine kidney contains a population of radiosensitive thymus-independent large interstitial cells that express a truncated TCR-alpha mRNA that is not associated with surface expression of functional TCR. These cells may have attempted to rearrange TCR-alpha genes, suggesting that they may be related to the lymphoid lineage.