In the absence of CD154, administration of interleukin-12 restores Th1 responses but not protective immunity to Schistosoma mansoni

The cytokine interplay during the development of protective immunity to the radiation-attenuated (RA) schistosome vaccine has been extensively characterized over recent years, yet the role of costimulatory molecules in the development of cell-mediated immunity is much less well understood. Here we demonstrate the importance of CD40/CD154 in vaccine-induced immunity, as CD154(-/-) mice exposed to RA schistosomes develop no protection to challenge infection. We showed that vaccinated CD154(-/-) mice have defective Th1-associated immune responses in the skin-draining lymph nodes and the lungs, with reduced or absent levels of interleukin-12p40 (IL-12p40), gamma interferon, and nitric oxide, but elevated levels of lung IL-4 and IL-5. The expression of major histocompatibility complex II (MHC-II) on antigen-presenting cells recovered from the lungs of vaccinated CD154(-/-) mice was also severely compromised. The administration of anti-CD40 monoclonal antibody (MAb) to CD154(-/-) mice did not reconstitute sustained Th1 responses in the lymph nodes or the lungs, nor did the MAb restore anti-parasite immunoglobulin G production or protective immunity. On the other hand, the administration of recombinant IL-12 (rIL-12) to CD154(-/-) mice shortly after vaccination caused elevated and sustained levels of Th1-associated cytokines, rescued MHC-II expression by lung CD11c(+) cells, and restored the appearance of inflammatory effector foci in the lungs. However, the treatment of CD154(-/-) mice with rIL-12 did not restore protection. We conclude that protective immunity to the RA schistosome vaccine is CD154 dependent but is independent of IL-12-orchestrated cellular immune mechanisms in the lungs.