Regulatory function of Thy1-negative cells. I.--Evidence for cells without the Thy1-surface marker and without phagocytic properties, enhancing the IgM antibody response.

Dextran-activated Thy1-cells are effective in enhancing the IgM anti-body response of syngeneic and allogeneic spleen cells to an unrelated antigen. This regulatory activity is mediated through a soluble B-cell-enhancing factor (BEF) which is released by activated cells. Removal of macrophages by silica-treatment does not abolish the regulatory activity of remaining cells. BEF can be considered as an auxiliary factor which does not substitute for either T cells or macrophages in in vitro antibody production.