Immobilized anti-CD3-induced T cell growth: comparison of the frequency of responding cells within various T cell subsets.

Human T cells can be divided into subsets based on the expression of CD29, CD45RA, CD45RO, LFA-3, or CD11a. It has been suggested that the subset of CD4+ T cells that expresses high densities of CD29, CD11a, CD45RO, and LFA-3 contains "memory" T cells, whereas the subset of cells that expresses CD45RA contains "naive" T cells. In order to obtain a more complete picture of the functional capacities of human naive and memory CD4+ and CD8+ T cell subsets, highly purified T cells were activated with a uniform stimulus and responses were examined in bulk cultures and under limiting dilution conditions. T cell activation was achieved with an immobilized mAb to the CD3 molecular complex, 64.1. In bulk cultures, immobilized 64.1 stimulated a vigorous response. Moreover, the number of cells entering the cell cycle, the magnitude of the [3H]thymidine incorporation, and the growth of the cells over 6 days in culture by naive and memory CD4+ T cells was comparable. To delineate the frequency of responsive cells in each subset more precisely, cells were cultured with immobilized 64.1 at limiting dilution and the precursor frequency of responding cells was assessed by examining wells microscopically for visible growth. Immobilized 64.1 was able to induce some T cells from each subset to grow in the complete absence of AC, when exogenous IL2 was present. The number of responding CD4+ and CD8+ cells was comparable. The percentage of naive cells responding in each population was approximately three times greater than the frequency of memory cells. IL4 could also support the growth of immobilized 64.1-activated CD4+ T cells, but the frequency of responding cells was much lower than that supported by IL2. The vast majority of the IL-4 responsive CD4+ cells resided within the naive cell subset. The data indicate that the response of CD4+ and CD8+ naive and memory T cell subsets to immobilized anti-CD3 depends on the density of responding cells. Naive T cells have an enhanced capacity to grow when cultured in the absence of other T cells or accessory cells. This ability may facilitate their expansion during primary immune responses.