We studied the role of the peripheral Tfh in DLBCL. Tfh were effective at promoting the proliferation of primary DLBCL tumor cells. Tfh were effective at inhibiting the apoptosis of primary DLBCL tumor cells. IL-10 secretion in Tfh was significant elevated in DLBCL. Neutralization of IL-10 compromised Tfh-mediated pro-tumor effects.