| Summary: | Rabbit antisera have been used to define 'constant region' markers which distinguish between mouse T cell-derived helper and suppressor factors, regardless of their antigen-specificity or strain of origin. These antisera have also been shown to bind to functional T-cell lines. After several absorption steps, rabbit anti-helper factor serum bound specifically to mouse helper cell lines, whereas rabbit anti-suppressor factor serum bound specifically to suppressor cell lines. Neither antiserum bound to cytotoxic T cell lines. The 'isotypic' determinants defined by these antisera were demonstrated to be present on distinct subpopulations of non-transformed T cell populations, such as splenic T cells, cortisone-resistant thymocytes and Con A blasts, but were not found on Thy-1- spleen cells, bone marrow, brain, heart, liver, kidney or heart tissue. The antisera did not stain significant numbers of normal thymocytes, and so expression was restricted to mature T cells. T cells reactive with rabbit anti-helper factor serum were found in the Lyt 2- population of cortisone-resistant thymocytes, and constituted a major subpopulation of in vitro induced helper cells, while rabbit anti-suppressor factor serum stained cells found in the Lyt 2+ population of cortisone-resistant thymocytes, as well as the majority of in vitro induced suppressor cells. Thus, these antisera are potentially of great value in the definition and isolation of functionally-distinct T cell subpopulations.
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