γδ T cells provide potent B-cell help. (A) Activation-dependent expression of costimulatory molecules in γδ T cells is delayed but sustained. Flow cytometric analysis of costimulatory molecules on peripheral blood γδ T cells that were analyzed either immediately after isolation (top row) or after 36 hours (middle row) and 84 hours (lower row) of stimulation with IPP. Culturing of γδ T cells in the absence of TCR triggering (but in the presence of IL-2) did not result in marked expression of costimulatory molecules, as evidenced in cells at 84 hours of culture (dashed line). Control Ab stainings are shown in filled histograms. (B) γδ T cells induce Ab production during coculture with B cells. Tonsillar B cells were cultured alone (-)orin the presence of CXCR5-negative αβ T cells (T_C), T_FH cells (T_FH), or peripheral blood γδ T cells (γδ T) without addition of exogenous cytokines; after 10 days the Ab titers in the culture supernatants were determined by ELISA. One of 4 representative experiments is shown.