Cutting edge: The IgG response to the circumsporozoite protein is MHC class II-dependent and CD1d-independent: Exploring the role of GPIs in NK T cell activation and antimalarial responses

Biochemical analysis has suggested that self GPI anchors are the main natur al ligand associated with mouse CD1d molecules, A recent study reported tha t V alpha 14(+) NK T cells responded to self as well as foreign (parasite-d erived) GPIs in a CD1d-dependent manner. It further reported that the IgG r esponse to the Plasmodium berghei malarial circumsporozoite (CS) protein wa s severely impaired in CD1d-deficient mice, leading to a model whereby NK T cells, upon recognition of CD1d molecules presenting the CS-derived GPI an chor, provide help for B cells secreting anti-CS Abs. We tested this model by comparing the anti-CS Ab responses of wild-type, CD1d-deficient, and MHC class II-deficient mice. We found that the IgG response to the CS protein was solely MHC class II-dependent. Furthermore, by measuring the response o f a broad panel of CD1d-autoreactive T cells to GPI-deficient CD1d-expressi ng cells, we found that GPIs were not required for autoreactive responses.