The fraction 1 and V protein antigens of Yersinia pestis activate dendritic cells to induce primary T cell responses.

The F1 and V antigens of Yersinia pestis, despite acting as virulence factors secreted by the organism during infection, also combine to produce an effective recombinant vaccine against plague, currently in clinical trial. The protective mechanisms induced by rF1 + rV probably involve interactions with dendritic cells (DC) as antigen uptake, processing and presenting cells. To study such interactions, naive ex vivo DC from bone marrow, spleen and lymph node were cultured with rF1, rV or combined antigens and demonstrated to secrete interleukin (IL)-4 and IL-12 into the culture supernatant. Cytokine production in response to pulsing was dependent on the maturity of the bone marrow-derived DC culture, so that pulsed 8-day-old cultures had accumulated significantly more intracellular IL-4 and IL-12 than unpulsed cells. DC, pulsed with rF1 + rV for 2-24 h, were able to prime naive autologous lymph node T cells to proliferate in an antigen dose-dependent manner, with an order of potency of 3d bone marrow-derived DC (BMDC) > 7d BMDC > splenic DC. Significantly, cell-free supernatants from rF1 + rV-pulsed BMDC and splenic DC were also able to induce specific primary responses effectively in naive T cells, suggesting that these supernatants contained stimulatory factor(s). This study suggests an important role for DC, or factors secreted by them, in the induction of protective immunity to plague by the rF1 and rV antigens.