Antibodies to beta 2-microglobulin, the light-chain component of class I histocompatibility molecules, provide an activation signal to human lymphocytes

Antibodies to beta 2-microglobulin (beta 2m), the light-chain component of class I histocompatibility antigens, provide a strong co-stimulatory signal to human lymphocytes in the presence of phorbol ester. This activation signal requires a high concentration of antibody, whereas the effect on responses to a mitogenic lectin is exclusively inhibitory over a broad dose range. A rabbit polyclonal and a mouse monoclonal antibody to beta 2m were similarly co-stimulatory. Antibody to beta 2m was co-stimulatory with phorbol ester, but not calcium ionophore, suggesting that class I antigens play a role in the initiation of the 'first' signal of a recently described two-signal model of lymphocyte activation.