The mechanism of experimental autoimmune encephalomyelitis tolerance induced by stress-related chaperone Hsp70 complexed with endogenous peptides depends on H60 and NKG2D interaction

Background: Inflammatory processes induce a site stress response which might be important in the recovery phase. Objective: Hsp70 complexed with endogenous peptides (Hsp70-pc) induces tolerance to experimental autoimmune encephalomyelitis (EAE); however, the mechanisms of this effect are not well understood. Methods: To assess Hsp70-pc-induced tolerance the effect of preinjection with anti-H60 and anti-NKG2D antibody on EAE in SJL/J was examined. We estimated function of dendritic and NK cells in co-culture with proteolipid protein (PLP)-reactive T cells. Assessment of PLP-reactive T-cell death and number of Treg cells was done by flow cytometry. Results: Peptides derived from brain tissue of mice with EAE complexed with stress-induced chaperone, hsp70 (Hsp70-pc) induced an NK-cell-dependent tolerance for subsequent EAE sensitization. We have shown that the MHC class I-related glycoprotein H60 determines Hsp70-pc-induced EAE inhibition. Hsp70-pc led to significant and selective upregulation of H60 expression in SJL/J mice, and antibody blocking of H60 expression led to loss of EAE tolerance. Similarly, blocking of the NK cell receptor for H60, NKG2D, also reversed the Hsp70-pc-induced EAE inhibition. In contrast, in C57BL/6 mice in which H60 was naturally not expressed, Hsp70-pc-induced tolerance was not detected. Direct killing of H60+ PLP-reactive cells seems not to be involved in the Hsp70-pc-induced tolerance mechanism as no enhanced loss of CD3+H60+ over CD3+H60- cells in Hsp70-pc-induced EAE tolerance was found. The NK cell-mediated Hsp70-pc-induced tolerance to EAE was dependent on modulation of dendritic cell (DC) function. Similarly, we have not seen increased number of Tregs, CD4+ CD25+ FoxP3+ T cells. In co-culture system, DC from mice treated with Hsp70-pc with PLP-reactive cells reduced proliferative response to PLP. The mechanism of reduced PLP reactivity involved enhanced autoreactive cell death as shown by Annexin V and 7AAD staining. Conclusions: These findings might be of significance in tailoring immune regulatory strategies for autoimmune diseases such as multiple sclerosis.