LYMPHOCYTES BEARING THE GAMMA-DELTA T-CELL RECEPTOR IN ACUTE BRUCELLA-MELITENSIS INFECTION

A phenotypical analysis carried out by indirect immunofluorescence and two-color cytofluorometry showed that the number of lymphocytes beari ng the gammadelta T cell receptor (TcR) heterodimer was dramatically i ncreased in the blood of six children with Brucella melitensis infecti on. Most in vivo expanded gammadelta T cells reacted with a monoclonal antibody which identifies Vdelta2 gene products and a significant pro portion expressed CD25 and HLA-DR activation antigens. In addition, wh ereas only a few gammadelta T lymphocytes were CD8+, nearly all were C D4-. Highly enriched populations of both alphabeta and gammadelta T ce lls were obtained by negative immunoselection from three subjects with brucellosis sampled during convalescence. Despite the different form of their TcR, the proliferation of these two major T cell subsets in r esponse to a mitogenic anti-CD3 monoclonal reagent (OKT3) was optimal. In contrast, alphabeta, but not gammadelta, T lymphocytes proliferate d vigorously in response to the antigenic stimulus elicited by heat-ki lled Brucella. Further studies are, therefore, needed to determine whe ther the selective expansion of the gammadelta T cell subpopulation ob served during the clinical course of the infection is driven by antige nic determinant(s) borne by the pathogen in vivo or is due to host-der ived stimuli, such as autologous heat-shock proteins expressed on the surface of the infected cells.