Identification of lymphocyte subpopulations in E-RFC-enriched and E-RFC-depleted cell fractions of fresh and cryopreserved lymphocytes.

Fresh lymphocytes and frozen-stored lymphocytes were separated into E-RFC-enriched and E-RFC-depleted cell fractions by density gradient centrifugation of sheep red blood cell (SRBC) rosette-forming cells (E-RFC), since the ability to form rosettes is primarily a T cell characteristic. Subpopulations of lymphocytes were identified, demonstrating the presence of cell surface markers: T cell specific antigens (T+), receptors for SRBC on T cells (E-RFC), Fc-receptors (FcR) for IgG type antibodies, and surface Ig (sIg). Our results indicate that, although the E-RFC-depleted fraction contains virtually no cells capable of binding SRBC, there is still a considerable proportion of T cells present in that fraction, as detected with the anti-T cell antiserum. Moreover, data are presented to indicate that the E-RFC-enriched fraction does not consist exclusively of T lymphocytes. Since this separation procedure is used frequently for the identification of the nature of effector cells in cell-mediated (CMC) and antibody-dependent cellular cytotoxicity (ADCC) assays, the identification of T cells in purified lymphocyte fractions by means of SRBC rosette formation may lead to a false conclusion as to the nature of the effector cells.