In vitro activation leads to the binding of T-cell markers to the surface of B-lymphocytes

The aim of the present study was to determine whether activation of human T-cells in vitro results in the expression of markers characteristic for T-cells on the surface of B-lymphocytes and to correlate antigenic changes with the release of soluble T-cell antigens. Peripheral blood lymphocytes (PBL) were exposed in vitro to phytohemagglutinin (PHA) for 3 days. Changes in the phenotype of the cells were determined by flow cytometry and the level of soluble T-cell antigens was assessed by ELISA. PHA-activated PBL released elevated quantities of soluble CD2, CD4, and CD8 compared with control cultures. Following PHA stimulation the proportion of CD4⁺CD8⁺ and HLA-DR⁺ cells increased. In addition, after 3 days of activation with PHA about 80% of the CD19⁺ cells (B-cells) reacted with F(ab)₂ fragments of CD2 monoclonal antibodies (MoAbs). A high proportion of B-cells in activated cultures also reacted with F(ab)₂ fragments of anti-CD8 MoAb and anti-CD4 MoAb. The removal of either CD4⁺ or CD8⁺ T-cells from the cultures prior to stimulation with PHA drastically reduced the proportion of B-cells expressing CD4 or CD8, respectively. The attachment of T-cell markers to the surface B-lymphocytes may constitute a new mechanism for B-cell regulation by T-cells.