Biochemical identification of I-J as a novel dimeric surface molecule on mouse helper and suppressor T cell clones

A monoclonal anti-1-J(k) antibody JK10-23 was capable of precipitating the putative I-J(k) molecule from NP-40 lysates of I-125-surface labelled mouse T cell clones with either helper or suppressor functions. The I-J molecule detected by specific immunoprecipitedion and subsequent one- or two-dimensional gel analysis was a Mr 84-90 K dimer composed of 42-46 K glycopeptide subunits having isoelectric point pH 5.3 to 6.4. A monomeric form of I-J also existed in some of the T cell clones. The I-J subunit was a glycosylated polypeptide with a 41 K backbone having at least two glycosylation sites. I-J was distinguishable from other known dimeric T cell surface molecules with comparable molecular size, that is, T cell receptor 43 heterodimer, A1 and YE molecules expressed on a T cell leukemia EL4, and mouse CD28. The I-J(k) molecule was precipitable from T cell clones with I-A(k) and I-E-k restriction specificities Including a clone derived from an H-2(b) -> H-2(bxk)F(1) radiation bone marrow chimera. None of the H-2(b)-restricted T cell clones from H-2(b) and its F-1 showed the I-J(k) immunoreactivity. T cell clones having either I-A(b) or I-E-k restriction specificities derived from Intra-H-2 recombinant mouse B10.A(5R) were positive for the I-J(k), while an I-A(b)-restricted T cell clone from B10.A(3R) was negative in the I-J(k) immunoprecipitation. The results indicate that I-J is a novel dimeric surface molecule, most likely to be a homodimer, expressed on T cells according to the major histocompatibility complex.