Vγ9Vδ2 T cells use a combination of mechanisms to limit the spread of the pathogenic bacteria Brucella

Human V gamma 9V delta 2 T cells play a crucial role in early immune response to intracellular pathogens. In brucellosis infection, this population of cells is drastically increased in the peripheral blood of patients during the acute phase of infection. In vitro, V gamma 9V delta 2 T cells exhibit strong cytolytic activity against Brucella-infected cells and are able to impair intracellular growth of Brucella suis in autologons macrophages. In this study, we have investigated the relative importance of contact-dependent mechanisms versus soluble factors in the intracellular growth and viability of B. suis. We show that V gamma 9V delta 2 T cells use contact-dependent mechanisms, such as the release of lytic granules and Fas-mediated signals, to decrease intracellular B. suis through lysis of infected macrophages, but these mechanisms have little impact on Brucella survival. Moreover, we demonstrate that soluble factors secreted by V gamma 9V delta 2 T cells can directly affect B. suis survival through their potent bactericidal effects. From these results, we conclude that V gamma 9V delta 2 T cells are able to use a combination of mechanisms that reduce the total numbers of B. suis and thus, may benefit the host by limiting the spread of this intracellular pathogen.