Human peripheral blood T cells proliferate in response to Escherichia coli and Pseudomonas aeruginosa. We observed that during the first few days after stimulation a large percentage of the responding PBMC were gamma delta T cells. In our study we characterized the early T cell responses of freshly isolated adult and newborn PBMC to soluble preparations of heat-killed E. coli and P. aeruginosa. Specimens from all healthy adults tested showed intense proliferation in response to both bacterial preparations; at 6 days, the responding cells were mainly T cell blasts, of which high percentages (up to 80%) were gamma delta T cells, most expressing V delta 2/V gamma 9. All newborn blood specimens tested also showed T cell proliferative responses, which included a marked expansion of gamma delta T cells, mainly of the V delta 1 subset. Populations of purified V delta 1 and V delta 2 T cells were obtained from adult PBMC following stimulation with E. coli; both subsets proliferated upon rechallenge with the bacterial preparations. Protease treatment of the bacterial preparations did not appreciably affect their ability to induce expansion of gamma delta T cells in either adult or cord blood, indicating that the stimulatory components were not proteins. The response of gamma delta T cells from newborns indicates that prior exposure to bacterial products is not necessary and suggests that gamma delta T cells are important elements in natural immunity to these extracellular organisms.

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