MHC-independent genetic factors control the magnitude of CD4+ T cell responses to amyloid-ß peptide in mice through regulatory T cell-mediated inhibition.

Accumulation of amyloid-ß peptide (Aß) is considered the triggering factor of pathogenic lesions in Alzheimer's disease (AD), and vaccines targeting Aß are promising therapeutic options. However, the occurrence of meningoencephalitides attributed to T cell responses in 6% of Aß-immunized patients underscores the need for a better understanding of T cell responses to Aß. We characterized the parameters controlling the magnitude of Aß-specific CD4(+) T cell responses in mice. T cell responsiveness to Aß1-42 was highly heterogeneous between mouse strains of different H-2 haplotypes, with SJL/J (H-2(s)) mice displaying a strong response, mainly specific for Aß10-24, and C57BL/6 (H-2(b)) mice displaying a weak response to Aß16-30. Surprisingly, C57BL/6 mice congenic for the H-2(s) haplotype (B6.H-2(S)), which display a "permissive" MHC class II allele for presentation of the immunodominant Aß10-24 epitope, showed a very weak CD4(+) T cell response to Aß, suggesting that MHC-independent genes downmodulate Aß-specific CD4(+) T cell responses in C57BL/6 background. Vaccine-induced CD4(+) T cell responses to Aß were significantly enhanced in both C57BL/6 and B6.H-2(S) mice upon depletion of regulatory T cells (Tregs), whereas Treg-depleted SJL/J mice displayed unaltered Aß-specific T cell responses. Finally, Treg depletion in C57BL/6 transgenic APPPS1 mice, a mouse model of AD, results in enhanced vaccine-induced CD4(+) T cell responses in AD compared with wild-type animals. We concluded that the magnitude of Aß-specific CD4(+) T cell responses is critically controlled in both physiological and pathological settings by MHC-independent genetic factors that determine the overall potency of Aß-specific Treg responses.