In vivo and in vitro activation and expansion of gamma delta T cells during Listeria monocytogenes infection in humans

Serial flow cytometry analyses of peripheral blood mononuclear cells obtained from 8 patients infected with Listeria monocytogenes showed a higher percentage (P < 0.01) of gamma delta T cells (median, 11.7; range, 3.7 to 353) than did 16 age-matched uninfected controls (1.7, 0.4 to 13). Most in vivo-expanded gamma delta T cells expressed the V gamma 9 and V delta 2 gene products and displayed a memory phenotype (CD45RO(high)), and patients' gamma delta T cells expressed significantly more (P < 0.01) activation marker HLA-DR than did controls (19.8% [median] and 0.9 to 87.6% [range] versus 2.3% and 0 to 4.7%, respectively). When peripheral blood mononuclear cells from normal donors were cultured in vitro with heat-killed Listeria cells, analysis of CD25 and HLA-DR expression on gamma delta and alpha beta T cells indicated that a high percentage of gamma delta T cells was activated early compared to alpha beta T cells. In addition, depletion of gamma delta T cells before culture abrogated the early lymphocyte proliferative response induced by the pathogen, Taken together, these results argue for the involvement of gamma delta T cells during L. monocytogenes infection in humans.