MITOGENIC EFFECT OF ALPHA-1-MICROGLOBULIN ON MOUSE LYMPHOCYTES - EVIDENCE OF T-CELL AND B-CELL COOPERATION, B-CELL PROLIFERATION, AND A LOW-AFFINITY RECEPTOR ON MONONUCLEAR-CELLS

Human α1‐m microglobulin (α1‐m), a low molecular weight plasma protein, was found to exert mitogenic effects on mouse lymphocytes from lymph nodes and spleen. The stimulatory effects appeared lo be strain‐restricted: α1‐m induced a varying degree of proliferation of lymphocytes from three strains, whereas one strain responded poorly. Experiments with lymphocyte subpopulations showed only weak stimulatory effects of α1‐m on purified T and B lymphocytes cultivated alone. The addition of mitomycin‐treated cells of the other subpopulation could not restore the proliferative responses in either T or B lymphocytes. Strong stimulations were recorded only when both T and B lymphocytes were present, indicating that the T and B lymphocytes cooperate to achieve the proliferation However, FACS studies on cultured splenocytes indicated (hat the proliferating cells are predominantly B lymphocytes. These data extend our earlier findings of a mitogenic effect of α1‐m on guinea pig lymphocytes. Furthermore. results were obtained indicating the presence of a receptor on mononuclear cells. Iodine‐labelled α1‐m was bound lo mononuclear cells prepared from spleens, and the binding could be blocked by an excess of non‐labelled α1‐m. Scatchard plotting of the data gave an equilibrium constant of 0.7 × 105/M for the binding between α 1‐m and the receptor. Together with the documented inhibitory activity of α1‐m on antigen‐driven proliferation of lymphocytes, these results suggest an immunoregulatory role for α1‐m. Copyright © 1990, Wiley Blackwell. All rights reserved