Peter C. L. Beverley

A group of mAb recognizing the 200- and/or 220-kDa determinants (CD45R) of the leukocyte common Ag such as 2H4, WR16, MD4.3, and SN130 cross-block each other showing that they recognize a closely related epitope. The antibody UCHL1 reacts with a 180-kDa determinant of the leukocyte common Ag and exhibits a reciprocal T subset distribution pattern to the CD45R group. Peripheral blood T cells were 40% positive for UCHL1 and 58 to 65% positive for the CD45R antibodies; less than 1% of cells stained for both. On activation of CD45R+,UCHL1- T cells by PHA, up to 40% of cells became positive for both CD45R and UCHL1 by day 3. By day 7, CD45R+,UCHL1- cells fell from 90 to less than 21% whereas UCHL1+,CD45R- cells rose from 2 to 93%. Conversely, PHA-stimulated UCHL1+,CD45R- cells remained UCHL1+,CD45R- during the 7 days in culture showing that phenotypic change was unidirectional from CD45R+ to UCHL1+. In primary allogeneic mixed lymphocyte reactions, activated CD45R+ T cells also showed a change to UCHL1+. When these cells were rechallenged by the original alloantigen, the UCHL1+ cells showed 7- to 20-fold greater proliferation than the CD45R+ cells on day 3 after rechallenge. The recovery of virtually all alloantigen induced secondary proliferative response in the UCHL1+,CD45R- T cell population suggests that UCHL1 identifies a primed population of T cells which may include memory cells.

The monoclonal antibody UCHL1 identified an antigen present on most thymocytes, a subpopulation of resting T cells within both the CD4 and CD8 subsets, and on mature activated T cells. The UCHL1 determinant is also present on cells of the myeloid lineage, but not normal B cells or NK cells. Functionally, UCHL1 identifies a subpopulation of T cells which proliferates maximally to soluble antigen and provides maximum help for PWM-stimulated immunoglobulin synthesis. In contrast, the UCHL1- cells do not induce immunoglobulin synthesis and do not proliferate in the presence of soluble antigen, although both the UCHL1- and the UCHL1+ fractions of T cells proliferate well in the presence of PHA. By standard immunoprecipitation techniques and SDS page, the antigen recognized by UCHL1 was found to have a molecular weight of 180,000-185,000. Preclearing experiments using antibodies identifying the leucocyte common antigen, LCA, and the lymphocyte function-associated antigen, LFA-1, which have similar molecular weights to UCHL1, showed that the UCHL1 determinant is not biochemically related to these antigens.

The properties of human lymphocyte fractions isolated either by sheep red cell(E) rosetting or by fluorescence-activated cell sorting after staining with UCHT1 monoclonal anti-T cell antibody have been compared. Two populations of E+ cells with very different phenotype and function have been identified. E+/UCHT1+ cells respond well to the T cell mitogens phytohemagglutinin and concanavalin A and provide help for an in vitro specific antibody response. They can also suppress the antibody response of allegeneic peripheral blood mononuclear cells. In contrast, the E+/UCHT1- population, which has no other markers characteristic of T cells, fails to respond to mitogens or to provide help or suppression for an antibody response. These cells, however, are highly active natural killers. They possess Fc gamma receptors and have a characteristic staining pattern of nonspecific esterase enzyme activity. It is concluded that not all cells capable of forming E rosettes are thymus-processed cells and that this heterogeneity can be revealed by staining with the monoclonal anti-T cell reagent UCHT1.