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Surface antigenic specificities of human thymus-derived (T) lymphocytes were studied by cytotoxicity tests using a heterologous rabbit anti-human thymus serum. This serum showed higher cytotoxic titres on thymocytes by comparison with peripheral lymphocytes. After proper absorption the antiserum was non-toxic for chronic lymphatic leukaemia cells, but lysed tile majority of thymocytes. It also lysed some of peripheral lymphocytes. corresponding to those lymphocytes which bound sheep erythrocytes CE) hut not erythrocyte- antibody-complement complexes (EAC). Pretreatment of lymphocytes with the absorbed antiserum and complement. completely abrogated rosette formation with E but spared EAC-binding lymphocytes. It also eliminated their reactivity to phytohaemagglutinin and concanavalin A. These findings indicate that the absorbed serum causes selective lysis of I cells. The results obtained from quantitative absorption studies suggest that a certain loss of T-cell antigens is brought about during the differentiation of thymocytes into peripheral T cells. [ABSTRACT FROM AUTHOR]

Xenoantisera, designated AT48 and A172, were developed by immunizing rabbits with human thymus cell membrane and guinea-pigs with a T-cell glycoprotein purified from leukaemic T-cell membrane. Whereas AT48, after appropriate absorption, reacted exclusively with the majority of thymocytes (mainly cortical thymocytes) among normal lymphoid populations. AT72 reacted with virtually all of the thymus and T cells but not with B cells. Thymocytes, which were strongly reactive with AT72, existed in the thymic medulla, but cortical cells were also very weakly reactive with AT72. When cultured T-cell lines, all of which were derived from patients with T-cell-type acute lymphatic leukaemias, were tested for their reactivities with AT48 and AT72 by immunofluorescence. we found that AT48 stained certain T-cell lines, whereas AT72 stained all of the T-cell lines tested so far. Immunochemical data showed that AT48 precipitated a 48K molecular weight (mol. wt) glycoprotein from 125I-labelled thymus cell surface glycoproteins, which appeared to be very weakly associated with a 12K mol. wt component. These 48K and 12K mol. Wt. components precipitated by AT48 showed almost identical isoelectric points (pI) to those of HLA heavy chain and β2-microglobulin respectively. AT72, on the other hand, precipitated a 72K mol. Wt. glycoprotein from thymus and T cells as well as from leukaemic T cells. A less prominent 65K mol. wt glycoprotein was also precipitated by AT72 from thymus and T cells but not from leukaemic T cells. These two components showed almost identical pI ranging approximately from 4 to 7, and this marked charge heterogeneity observed was reduced by neuraminidase treatment, suggesting that it reflects the heterogeneity in sialylation of this molecular species. We concluded from these data that AT48 and AT72 used in this work could detect human homologues of mouse TL and Ly 1 antigens respectively. [ABSTRACT FROM AUTHOR]