Sheep CD4(+) alpha beta T cells express novel members of the T19 multigenefamily

The sheep T19 multigene family contains at least 50 genes which are thought to be expressed exclusively on gamma delta T cells. The archetypal T19 mol ecule (represented by a full-length cattle cDNA clone termed WC1) is though t to have a relative molecular mass of about 220000 and to contain 11 scave nger receptor cysteine rich (SRCR) repeats and a long cytoplasmic tail. In this study, purified CD4(+) and gamma delta TCR+ sheep lymphocytes were exa mined by reverse transcriptase-polymerase chain reaction for the expression of T19 molecules. As expected, gamma delta T cells were found to express T 19 molecules which closely resembled the archetypal form. However, CD4(+) c up T cells were found to express at least two different types of T19 molecu les; one resembled the previously described T19 molecules of gamma delta T cells which possessed the archetypal WC1-like structure, but a novel type o f T19 variant which lacked SRCR domains 10 and 11 was also found in CD4(+) T cells but not gamma delta T cells. This novel molecule exhibited an unusu al, incomplete SRCR repeat 9 joined directly to a hinge region. The transme mbrane and cytoplasmic domains of this unusual T19 variant resembled the ca t tie T19 clone WC1, except that a complete exon within the cytoplasmic reg ion was missing. These results, in contradistinction to existing serologica l data, suggest that expression of the T19 gene family is not confined to g amma delta T cells. Selected T19 genes are apparently expressed within CD4( +) T cells and possibly other lymphocytes as well.