The role of T cell help in the generation of αGal reactive antibodies
Introduction Natural antibodies specific for the carbohydrate antigen Galα1-3Gal (αGal) represent a major immune barrier to discordant xenotransplantation, and have been suggested to play an important role in immunity to pathogens. However, little is known about how production of antibodies with specificity for αGal is regulated. Using αGT knockout mice (GT0 mice), which like humans contain in their serum antibodies that bind αGal, we examined the role of T cells in production of αGal specific antibodies.
Materials and methods αGal knockout mice (GT0) were crossed with T cell receptor β knock-out mice (TCRβ0) to generate double-knockout mice (GT0/TCRβ). The ability of GT0/TCRβ0, GT0, TCRβ+, and GT+/TCRβ+ (wild-type) to produce αGal reactive natural antibodies, as well as αGal reactive antibodies following immunization with pig cells was examined.
Results GT0/TCRβ+ mice exhibited an age dependent increase in the serum titer of αGal reactive natural antibodies. In contrast, the level of αGal reactive natural antibodies in GT0/TCRβ0 did not exhibit an age dependent increase in titer, and the titer observed was significantly lower than in age matched GT0/TCRβ+ mice. Following immunization with pig cells, GT0/TCRβ+ exhibited a dramatic increase in the serum titer of αGal reactive antibodies. In contrast, immunization with pig cells had no effect on the level αGal reactive serum antibodies in GT0/TCRβ0 mice, although these mice were capable of mounting a T cell independent antibody responding to phosphorylcholine after immunization with Streptococcus pneumoniae strain R36A. Interestingly, treatment of GT0/TCRβ+ mice with anti-CD40L prior to immunization completely prevented sensitization to αGal by pig cell immunization.
Conclusion Our data suggest that αGal reactive natural antibodies can be either T cell dependent or independent. However, the majority of αGal reactive natural antibodies that develop over time without immunization, and antibodies produced following sensitization to pig cells are T cell dependent. Production of T cell dependent αGal reactive antibodies can be prevented by blocking the interaction of CD40 and CD40L.