Wednesday, August 23, 2017

MHC class II epitope presentation modulates microbiota and protects against autoimmunity

It is not clear how exactly microbiota modulates host's immune system. Evidence are largely based on empirical observations and nonspecific factors secreted by microbiota. Presently very little is known if microbiota-immune system interface is also controlled at the level of antigen-specific adaptive immune system.    
New study from Diane Mathis lab published in PNAS suggests it may be the case.
Her lab studies human type I diabetes (T1D) mouse model known as NOD. NOD mice lack MHC II allele, Eα. In this study they used NOD mice expressing Eα, referred as Eα16/NOD. In mating experiments, they noticed when Eα was expressed by female but not by male parent, baby mice with NOD genotype showed significant protection from developing T1D, suggesting protection was transmitted vertically from Eα16/NOD mother to NOD pups. Interestingly, this protection was lost when pregnant mothers (dams) were treated with antibiotics pointing towards role of microbiota.

Experiments with germ-free sterile mice confirmed this observation.

In summary, this study showed that MHC class II [epitope] presentation modulates composition of microbiota in such a way to harbor species protective against T1D. Again, the authors were unable to specifically pinpoint any specific mechanism of protection, though they reported increase in Foxp3+ Treg numbers in Eα16/NOD mice compared to NOD (but found no difference in microbiota bound to IgA between mouse strains). It is likely that epitope presentation at the level of adaptive CD4 T cells contributed to development of protective environment.

posted by David



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