RECEPTOR FOR ALPHA(1)-MICROGLOBULIN ON T-LYMPHOCYTES - INHIBITION OF ANTIGEN-INDUCED INTERLEUKIN-2 PRODUCTION

The human plasma protein alpha(1)-microglobulin (alpha(1)m) was found to inhibit the antigen-induced interleukin-2 (IL-2) production of two different mouse T-helper cell hybridomas. alpha(1)m isolated from huma n plasma and recombinant alpha(1)m isolated from baculovirus-infected insect cell cultures had similar inhibitory effects. Flow cytometric a nalysis showed a binding of plasma and recombinant alpha(1)m to the T- cell hybridomas as well as to a human T-cell line. Radiolabelled plasm a and recombinant alpha(1)m bound to the T-cell hybridomas in a satura ble manner and the binding could be eliminated by trypsination of the cells. The affinity constants for the cell binding were calculated to be 0.4-1 x 10(5) M-1 using Scatchard plotting, and the number of bindi ng sites per cell was estimated to be 5 x 10(5)-1 x 10(6). The cell-su rface proteins of one of the T-cell hybridomas were radiolabelled, the cells lysed and alpha(1)m-binding proteins isolated by affinity chrom atography. SDS-PAGE and autoradiography analysis of the eluate reveale d major bands with M-r-values around 70, 35 and 15 kDa. The results th us suggest that alpha(1)m binds to a specific receptor on T cells and that the binding leads to inhibition of antigen-stimulated IL-2. produ ction by T-helper cells.