Autoantigen immunization at different sites reveals a role for anti-inflammatory effects of IFN-γ in regulating susceptibility to experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis is induced in B10.PL (H-2 ^u) mice by immunization with the immunodominant N-terminal epitope of myelin basic protein, Ac1-9. In the present study, we show that the site of immunization impacts disease incidence and severity. This effect is more marked in female mice than in males. Although immunization in the flanks is effective in eliciting disease, delivery of Ag in the footpad and tailbase results in poor induction. Analyses of the immune responses in female mice following different immunization regimens indicates that resistance to disease is accompanied by higher levels of IFN-γ and CD11b⁺Gr-1^int myeloid cells. Such myeloid cells are known to have a suppressive function, and consistent with this knowledge, blockade of IFN-γ results in increased disease activity and decreased levels of splenic CD11b⁺Gr-1 ^int cells. Conversely, injection of adjuvants (CFA or Pam ₃CSK₄) in the footpad decreases experimental autoimmune encephalomyelitis incidence and severity. Our study indicates that the site of immunization can impact the magnitude of the ensuing inflammatory response, and that at a certain threshold a protective, regulatory circuit can be elicited.