THE TETRASPANIN PROTEIN CD82 ASSOCIATES WITH BOTH FREE HLA CLASS-I HEAVY-CHAIN AND HETERODIMERIC BETA(2)-MICROGLOHULIN COMPLEXES

CD82 is a tetraspan transmembrane protein on NK/LAK-susceptible target s. A single highly glycosylated protein of heterogeneous molecular mas s (50-90 kDa) was immunoprecipitated by anti-CD82 from Nonidet P-40 ly sates of various B cell lines, Raji, Daudi, 721, and 721.134. Using th e milder detergent holamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), additional proteins were coprecipitated with CD82 from surfac e iodinated B cell lines, including a major band at 45 kDa, identified as the HLA class I heavy chain by sequential immunoprecipitations and sequential immunoprecipitation-Western blot analysis. Cocapping exper iments confirmed the molecular association of CD82 and HLA class I at the cell surface of these B cell lines. CD82 could be coprecipitated w ith both mature and beta(2)-microglobulin (beta(2)m)-free heavy chains of MHC-I from CHAPS extracts. No association between MHC-I and CD82 w as found in the beta(2)m-deficient Daudi cell line or after co-in vitr o translation of CD82, MHC heavy chain, and beta(2)m mRNA. The most li kely source of free class I heavy chains at the cell surface is by dis sociation of beta(2)m-associated class I molecules. These results sugg est that association of CD82-MHC-I takes place at the cell surface and could interfere with the capacity of the MHC-I complex to protect tar gets from NK-mediated cytotoxicity.