APOPTOSIS OF GAMMA DELTA T-CELLS IN HUMAN EHRLICHIOSIS/

Expansion of activated T cells expressing the T-cell receptor (TCR) ga mma/delta, CD45RO, and HLA-DR antigens is a prominent feature of acute infection with Ehrlichia chaffeensis in humans. The fate of these act ivated cells and the resolution of the gamma/delta T-cell response wit h return to the usual alpha/beta T-cell populations in this disease ar e not clearly understood. At a morphologic level, apoptotic cells are present in the peripheral blood during the acute and resolution phases of the infection. Simple culture of density gradient-separated lympho cytes from the blood of patients with acute ehrlichiosis produced cell death rapidly in the media compared to alpha/beta T cells. This loss of viability after incubation was apparently mediated by apoptosis, ba sed on flow cytometric and morphologic analyses. The results suggest t hat most primed (CD45RO(+)) and activated (HLA-DR(+)) gamma/delta T ce lls in acute ehrlichiosis might be subject to removal from the body by programmed or apoptotic cell death.