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

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Abstract
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 UCHL l+, 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 UCHL 1+ 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 UCHL 1+ phenotype. The relation of post‐thymic T cell maturation and differential CD45 expression is briefly discussed.