Four distinct antigen systems on human thymus and T cells defined by monoclonal antibodies: immunohistological and immunochemical studies.

Human thymus and T cell antigens were identified by using four distinct monoclonal antibodies (MoAb), designated 2D5, 5B3, 7A5 and 9D4. 2D5 antibody reacted with most human thymocytes and a few peripheral lymphocytes as well as with a subpopulation (20%) of bone marrow cells, and precipitated a 45K molecular weight (mol. wt.) component from 125I-labelled thymus cell lysate. 7A5 antibody also reacted with the majority (80%) of thymocytes but neither with peripheral lymphocytes nor with bone marrow cells. The antigen detected by 7A5 was a glycoprotein consisting of 48K and 12K mol. wt. components, which were non-covalently associated with each other. 5B3 reacted with virtually all of human thymus and T cells but not with the majority of B cells and bone marrow cells. This reagent precipitated a 72K mol. wt. glycoprotein from thymus and T cells. An additional 65K mol. wt. glycoprotein was precipitated by 5B3 together with the 72K mol. wt. component, but with poor reproducibility. 9D4 antibody, on the other hand, reacted with a 200K mol. wt. component from thymus and T cells as well as 220K and 210K components from the non-T cell fraction of tonsil lymphocytes. Whereas antigens detected by 2D5 and 7A5 appeared to be highly expressed on cortical thymocytes, the antigen defined by 5B3 occurred much more abundantly on medullary thymocytes and peripheral T cells than on cortical thymocytes. Based on the data described above, it is suggested that 7A5, 5B3 and 9D4 MoAb recognize human homologues of mouse TL, Ly-1 and Ly-5 antigens, respectively, whereas 2D5 antibody seems to resemble OKT10, as described by others.