CLONING AND EXPRESSION OF A CDNA-ENCODING OVINE INTERLEUKIN-7

Using the polymerase chain reaction (PCR) and primers based on regions of homology between the human and murine intel leukin 7 (IL-7)-encoding cDNAs, we have amplified an ovine (ov) IL-7 cDNA from reverse-transcribed RNA extracted from concanavilin A (Con A)-activated ovine lymph-node cells. The nucleotide sequence of the cDNA and the predicted amino acid (aa) sequence showed significant homology to those of the human and murine molecules. The ovIL-7 cDNA encodes a 176-aa polypeptide that, based on analysis of murine IL-7, is processed to a protein of 151 aa. The cDNA was demonstrated to encode a protein with IL-7 biological activity. Supernatants from COS or CHO-K1 cells transfected with an expression vector containing the ovIL-7 cDNA were able to synergise with a suboptimal level of Con A to induce proliferation of ovine thymocytes. In addition, both supernatants were able to induce thymocyte proliferation, albeit at a reduced level, in the absence of Con A. Further experiments demonstrated that for induction of ovine thymocyte proliferation, recombinant (re)-ovIL-7 was able to synergise with re-human (h) IL-2 but not re-hIL-6 or tumor necrosis factor-alpha (re-hTNF alpha).