Heterogeneity of Antigen Molecules Recognized by Anti‐tax(1) Monoclonal Antibody Lt‐4 in Cell Lines Bearing Human T Cell Leukemia Virus Type I and Related Retroviruses

Using a monoclonal antibody, Lt‐4, directed against human T cell leukemia virus type I (HTLV‐I) trans‐activator (tax(1)) antigen, we examined the expression of tax(1) and related antigens in a variety of T cell lines bearing HTLV‐I and related retroviruses, simian T cell leukemia virus type I (STLV‐I) and HTLV‐II, by immunofluorescence and immunoblot assays. Lt‐4 reacted with all HTLV‐I‐bearing cell lines tested and five out of eight simian cell lines bearing STLV‐I, but not with an HTLV‐II‐bearing cell line. Lt‐4 detected 40 kd tax(1) antigen molecules in most HTLV‐I‐bearing cell lines except one cell line that expressed 39 kd tax(1) antigen. In the STLV‐I‐bearing T cell lines, tax(1)‐related antigen molecules detected by Lt‐4 were heterogeneous, having molecular weights in the range of 36–41 kd.