No abstract

T follicular helper (TFH) cells are critical initiators in the development of T cell-dependent humoral immunity and the generation of protective immunity. We demonstrate that TFH cell accumulation and Ab production are negatively regulated by B7-H1 (programmed death ligand 1) in response to both helminth infection and active immunization. Following immunization of B7-H1−/− mice with keyhole limpet hemocyanin or helminth Ags, there is a profound increase in induction of TFH cells as a result of increased cell cycling and decreased apoptosis relative to wild-type mice. The increase in TFH cells in the absence of B7-H1 was associated with significant elevations in Ag-specific Ig response. Cotransfer experiments in vivo demonstrated that B7-H1 expression on B cells was required for negatively regulating TFH cell expansion and production of Ag-specific Ig. Treatment of immunized wild-type mice with anti–B7-H1 or anti-programmed death 1 mAbs, but not anti–B7-DC, led to a significant expansion of the TFH cell population and an enhanced Ag-specific Ig response. Our results demonstrate that the coinhibitory B7-H1/programmed death 1 pathway can limit the expansion of TFH cells and constrain Ag-specific Ig responses. This finding has direct implications for investigations examining the feasibility of therapeutically manipulating this pathway and reveals new insights into the regulation of the humoral immune response.

No abstract

In conditions of optimal priming, the neonate possess competency to mount quantitatively adult-like responses. Vaccine formulations containing sufficiently potent adjuvants may overcome the neonates’ natural tendency for immunosuppression and provoke a similarly robust immune response. TLR expression on T cells represents the possibility of directly enhancing T cell immunity. We examined the ex vivo responsiveness of highly purified human cord blood-derived CD8+ T cells to direct TLR ligation by a repertoire of TLR agonists. In concert with TCR stimulation, only Pam3Cys (palmitoyl-3-Cys-Ser-(Lys)4) and flagellin monomers significantly enhanced proliferation, CD25+ expression, IL-2, IFN-γ, TNF-α, and intracellular granzyme B expression. TLR2 and TLR5 mRNA was detected in the CD8+ T cells. Blocking studies confirmed that the increase in IFN-γ production was by the direct triggering of surface TLR2 or TLR5. The simultaneous exposure of CD8+ T cells to both TLR agonists had an additive effect on IFN-γ production. These data suggest that a combination of the two TLR ligands would be a potent T cell adjuvant. This may represent a new approach to TLR agonist-based adjuvant design for future human neonatal vaccination strategies requiring a CD8+ component.