Xylaria hypoxylon Lectin as Adjuvant Elicited Tfh Cell Responses

Foot‐and‐mouth disease (FMD) caused by FMD virus (FMDV) is a major health and economic problem in the farming industry. Vaccination of livestock against this highly infectious viral disease is crucial, and inactivated FMD vaccine has been effective at controlling infection. However, accumulated data show that the inactivated vaccine generates weak immune responses and that the oil formulation results in undesirable side effects. Mushroom lectins have recently been shown to display adjuvant effects when incorporated into DNA vaccines. In this study, to enhance the cellular immune response of FMDV antigen (146S), C57BL/6 mice were immunized with 146S combined with Xylaria hypoxylon lectin (XHL). The oil formulation (146S/Oil) was served as control group. Strong humoral immune responses were elicited in mice immunized with 146S/XHL as shown by high 146S antigen‐specific IgG levels, and also in 146S/Oil group. Interestingly, XHL in conjunction with inactivated FMD vaccine activated strong Th1 and Tc1 cell responses, especially Tfh cell responses, in immunized mice. XHL stimulated dendritic cell maturation by upregulating expression of major histocompatibility complex II (MHCII) molecules and co‐stimulatory molecules CD40 and CD86 in immunized mice. No XHL‐specific IgG or inflammatory factors were detected indicating the safety of XHL as an adjuvant. Taken together, these results suggest the effectiveness of XHL at inducing cellular immune responses and therefore confirm its suitability as an adjuvant for inactivated FMD vaccine.