B-cell antigens within normal and activated human T cells

In this study we compared cell surface staining for human peripheral blood lymphocyte (PBL) CD antigens by flow cytometry, with staining obtained foll owing permeabilization of PBL using the Cytoperm method (Serotec). Six CD a ntigens (CD20, CD21, CD22, CD32, CD35 and major histocompatibility complex class II antigen) normally found on the surface of B cells, were also found to be expressed within T cells. We also showed, by immunoelectron microsco py, that these inappropriately expressed ('occult') CD antigens are located within cytoplasmic vesicles or within the rough endoplasmic reticulum. Fol lowing in vitro activation of T cells a distinct increase in expression of all of these cytoplasmic antigens was observed but staining at the cell sur face was, by comparison, weak. We therefore propose that up-regulation of v arious B-cell CD antigens occurs within the cytoplasm of T cells following activation and that these antigens may be synthesized and released into the fluid-phase as soluble immunoregulatory molecules.