β2-Microglobulin on the Cell Surface. Relationship to HL-A Antigens and the Mixed Leucocyte Culture Reaction

Fab'-fragments derived from antibodies against β₂-microglobulin will completely abolish the cytotoxic effect of antibodies against HL-A serological determinants. This is the result of the Fab'-fragments competing with the antibodies against the HL-A antigens for binding to the lymphocyte surface. Reciprocally, it is shown that Fab'-fragments against the HL-A alloantigenic structures impeded the binding of Fab'-fragments to cell surface bound β₂-microglobulin.
Fab'-fragments against β₂-microglobulin inhibit considerably the mixed leucocyte culture reaction (MLR). The main effect is on the responding cells, whereas when the stimulating cells are treated with Fab'-fragments against β₂-microglobulin they do not (or, at most, only slightly) change their characteristics in the MLR. Fab'-fragments against immunoglobulin light chains do not influence the MLR significantly, whereas Fab'-fragments against HL-A antigens depress the response.
Fab'-fragments against β₂-microglobulin do not interfere with the mitogenic stimulation of PHA, whereas Fab'-fragments from the antiserum used in this study against HL-A8 reduced the mitogenic effect of PHA considerably.