The ICOS molecule plays a crucial role in the development of mucosal tolerance.

The ICOS molecule stimulates production of the immunoregulatory cytokine IL-10, suggesting an important role for ICOS in controlling IL-10-producing regulatory T cells and peripheral T cell tolerance. In this study we investigate whether ICOS is required for development of oral, nasal, and high dose i.v. tolerance. Oral administration of encephalitogenic myelin oligodendrocyte glycoprotein (MOG) 35-55 peptide to ICOS-deficient (ICOS-/-) mice did not inhibit experimental autoimmune encephalomyelitis (EAE), T cell proliferation, or IFN-gamma production, in striking contrast to wild-type mice. Similarly, intranasal administration of MOG(35-55) before EAE induction suppressed EAE and T cell responses in wild-type, but not in ICOS-/-, mice. In contrast, ICOS-/- mice were as susceptible as wild-type mice to high dose tolerance. These results indicate that ICOS plays an essential and specific role in mucosal tolerance and that distinct costimulatory pathways differentially regulate different forms of peripheral tolerance. Surprisingly, CD4+ cells from MOG-fed wild-type and ICOS-/- mice could transfer suppression to wild-type recipients, indicating that functional regulatory CD4+ cells can develop in the absence of ICOS. However, CD4+ T cells from MOG-fed wild-type mice could not transfer suppression to ICOS-/- recipients, suggesting that ICOS may have a key role in controlling the effector functions of regulatory T cells. These results suggest that stimulating ICOS may provide an effective therapeutic approach for promoting mucosal tolerance.

Genetic background determines the requirement for B7 costimulation in induction of autoimmunity.

B7 costimulatory molecules play an important role in inducing autoimmunity, tumor immunity, and transplant rejection, and therapeutic manipulation of B7 is being investigated in human diseases. To determine whether B7 costimulation is essential for inducing autoimmunity on different genetic backgrounds, we backcrossed B7.1/B7.2 deficient ((-/-)) mice on to the C57BL/6 (B6) and SJL backgrounds and induced experimental autoimmune encephalomyelitis (EAE) in these mice. B7.1/B7.2(-/-) mice on the B6 background were resistant to EAE induced with MOG 35-55, whereas the SJL B7.1/B7.2(-/-) mice were susceptible to PLP 139-151 or PLP 178-191-induced EAE. The SJL B7.1/B7.2(-/-) mice had a qualitatively different lesion pattern in that they showed increased white matter vacuolation compared to wild-type SJL mice when immunized with either PLP 139-151 or PLP 178-191. (B6xSJL)F1 B7.1/B7.2(+/+) mice were susceptible to EAE whereas (B6xSJL)F1 B7.1/B7.2(-/-) mice were resistant to EAE induced with either encephalitogenic peptide. Thus, genetic background determines the B7 requirement for inducing autoimmunity. These data have important implications for developing B7-based immunotherapies for human diseases.