Functional characteristics of 197+ CD4- CD8- sheep T lymphocytes: expansion and differentiation of peripheral T cells.

This report describes the results of functional studies on the CD3+ 197+ CD4- CD8- TCR gamma/delta + peripheral T lymphocyte of sheep. Cell types were identified by immunofluorescent and immunoenzymic staining and separated by fluorescence activated flow cytometry. Newly synthesized DNA was labelled in vivo by incorporation of 5-bromo-2-deoxyuridine (BrdU), and total DNA by in vitro incubation with propidium iodide. Cells were challenged in vivo with alloantigens, in vitro with alloantigens or a range of mitogens, and activation/differentiation was assessed by determination of cell number, phenotype, and thymidine incorporation. In normal lambs the 197+ cells showed no in vivo DNA synthesis except at a low level in the ileocaecal lymph node. A similarly low level of synthesis in the prescapular node was induced by local allogeneic challenge. A higher proportion of 197+ cells than of other T cells isolated from blood and lymph had G2/M phase DNA content, while very few had S phase DNA content. The response of 197+ cells in terms of change in relative numbers following in vivo allogeneic challenge was quite different to that of CD4+ or CD8+ cells. Instead of rising to a peak at 5-8 days after challenge and then declining, the percentage of 197+ cells rose steadily with no evidence of decline by 14 days. Purified 197+ cells were activated in vitro by phytohaemagglutinin (PHA) and concanavalin-A (Con-A) but not by B cell mitogens; such activation was dependent on the inclusion of feeder cells or interleukin-2 (IL-2).(ABSTRACT TRUNCATED AT 250 WORDS)