Reduced immunogenicity of Plasmodium falciparum gamete surface antigen (Pfs48/45) in mice after disruption of disulphide bonds – evaluating effect of interferon‐γ‐inducible lysosomal thiol reductase. Issue 4 (29th June 2016) - Merino, Kristen M.
Summary: Sexual stages of Plasmodium are critical for malaria transmission and stage‐specific antigens are important targets for development of malaria transmission‐blocking vaccines. Plasmodium falciparum gamete surface antigen (Pfs48/45) is important for male gamete fertility and is being pursued as a candidate vaccine antigen. Vaccine‐induced transmission‐blocking antibodies recognize reduction‐sensitive conformational epitopes in Pfs48/45. Processing and presentation of such disulphide‐bond‐constrained epitopes is critical for eliciting the desired immune responses. Mice lacking interferon‐ γ ‐inducible lysosomal thiol reductase (GILT), an enzyme that mediates reduction of S‐S bonds during antigen processing, were employed to investigate immunogenicity of Pfs48/45. It has been well established that the ability to reduce S‐S bonds in antigens guides effective T‐cell immune responses; however, involvement of GILT in the induction of subsequent B‐cell responses has not been explored. We hypothesized that the ability to reduce S‐S bonds in Pfs48/45 will impact the generation of T‐cell epitopes, and so influence helper T‐cell responses required for specific B‐cell responses. Non‐reduced and reduced and alkylated forms of Pfs48/45 were employed to evaluate immune responses in wild‐type and GILT knockout mice and studies revealed important differences in several immune response parameters, including differences in putative T‐cell epitope recognition, faster kinetics of waning of Pfs48/45‐specific IgG1 antibodies in knockout mice, differential patterns of interferon‐ γ and interleukin‐4 secretions by splenocytes, and possible effects of GILT on induction of long‐lived plasma cells and memory B cells responsible for antigen‐recall responses. These studies emphasize the importance of antigen structural features that significantly influence the development of effective immune responses. Abstract : The malaria vaccine candidate antigen Plasmodium falciparum gamete surface antigen (Pfs48/45) contains functional reduction‐sensitive conformational epitopes. The role of interferon‐ γ ‐inducible lysosomal thiol reductase (GILT), an enzyme that mediates reduction of S‐S bonds during antigen processing was investigated. Studies revealed important differences between wild‐type (WT) and GILT −/− mice in putative T‐cell epitope recognition, kinetics of Pfs48/45‐specific IgG1 antibodies, differential patterns of interferon‐ γ and interleukin‐4 secretions and on induction of long‐lived plasma cells and memory B‐cell responses.