Limiting dilution analysis of proliferative responses in human lymphocyte populations defined by the monoclonal antibody UCHL1: implications for differential CD45 expression in T cell memory formation.

Using limiting dilution analysis, we investigated proliferative responses of UCHL1+ and UCHL1- T cell populations to compare the precursor cell frequencies following recall and alloantigen stimulation, and the complexity of cellular interactions within UCHL1+ and UCHL1- populations. We find high frequencies of recall antigen responses among UCHL1+, but not UCHL1- T cells. In contrast, both populations contain similar frequencies of alloantigen responsive cells. Our results are consistent with single-hit kinetics in recall as well as alloantigen responses and show no complex cellular interactions within the responding populations. In conclusion, the difference between the recall antigen response of UCHL1+ and UCHL1- cells observed in conventional proliferation assays is most probably due to a high frequency of recall antigen-responsive UCHL1+ cells and not to suppressive phenomena in the UCHL1- population. These data suggest that memory T cells are largely of the UCHL1+ phenotype. The relation of post-thymic T cell maturation and differential CD45 expression is briefly discussed.