SHP-1 deficiency and increased inflammatory gene expression in PBMCs of multiple sclerosis patients

MHC variant peptide-mediated anergy of encephalitogenic T cells requires SHP-1

Our lab has demonstrated that encephalitogenic T cells can be effectively anergized by treatment with MHC variant peptides, which are analogues of immunogenic peptides containing an amino acid substitution at an MHC anchor residue. The MHC variant peptide of myelin oligodendrocyte glycoprotein (MOG)(35-55) proves an effective treatment as it does not induce symptoms of experimental autoimmune encephalomyelitis and fails to recruit macrophages or MOG(35-55)-specific T cells to the CNS. In this study, we sought to characterize the signaling pathways required for the induction of anergy by building upon the observations identifying the tyrosine phosphatase SHP-1 as a critical regulator of T cell responsiveness. Motheaten viable heterozygous mice, which contain a mutation in the SHP-1 gene resulting in a reduction in functional SHP-1, were challenged with MOG(35-55) or the MOG(35-55) MHC variant 45D. These mice display symptoms of experimental autoimmune encephalomyelitis upon immunization with MHC variant peptide and have significant CNS infiltration of tetramer-positive CD4(+) cells and macrophages, unlike B6 mice challenged with the variant peptide. The effects of SHP-1 are directly on the T cell as Motheaten viable heterozygous mice autoreactive T cells are not anergized in vitro. Lastly, we demonstrate no distinguishable difference in the initial interaction between the TCR and agonist or MHC variant. Rather, an unstable interaction between peptide and MHC attenuates the T cell response, seen in a decreased half-life relative to MOG(35-55). These results identify SHP-1 as a mediator of T cell anergy induced by destabilized peptide:MHC complexes.

Modulation of macrophage infiltration and inflammatory activity by the phosphatase SHP-1 in virus-induced demyelinating disease

The protein tyrosine phosphatase SHP-1 is a crucial negative regulator of cytokine signaling and inflammatory gene expression, both in the immune system and in the central nervous system (CNS). Mice genetically lacking SHP-1 (me/me) display severe inflammatory demyelinating disease following inoculation with the Theiler's murine encephalomyelitis virus (TMEV) compared to infected wild-type mice. Therefore, it became essential to investigate the mechanisms of TMEV-induced inflammation in the CNS of SHP-1-deficient mice. Herein, we show that the expression of several genes relevant to inflammatory demyelination in the CNS of infected me/me mice is elevated compared to that in wild-type mice. Furthermore, SHP-1 deficiency led to an abundant and exclusive increase in the infiltration of high-level-CD45-expressing (CD45(hi)) CD11b(+) Ly-6C(hi) macrophages into the CNS of me/me mice, in concert with the development of paralysis. Histological analyses of spinal cords revealed the localization of these macrophages to extensive inflammatory demyelinating lesions in infected SHP-1-deficient mice. Sorted populations of CNS-infiltrating macrophages from infected me/me mice showed increased amounts of viral RNA and an enhanced inflammatory profile compared to wild-type macrophages. Importantly, the application of clodronate liposomes effectively depleted splenic and CNS-infiltrating macrophages and significantly delayed the onset of TMEV-induced paralysis. Furthermore, macrophage depletion resulted in lower viral loads and lower levels of inflammatory gene expression and demyelination in the spinal cords of me/me mice. Finally, me/me macrophages were more responsive than wild-type macrophages to chemoattractive stimuli secreted by me/me glial cells, indicating a mechanism for the increased numbers of infiltrating macrophages seen in the CNS of me/me mice. Taken together, these findings demonstrate that infiltrating macrophages in SHP-1-deficient mice play a crucial role in promoting viral replication by providing abundant viral targets and contribute to increased proinflammatory gene expression relevant to the effector mechanisms of macrophage-mediated demyelination.

Induction of IL-33 expression and activity in central nervous system glia

IL-33 is a novel member of the IL-1 cytokine family and a potent inducer of type 2 immunity, as mast cells and Th2 CD4+ T cells respond to IL-33 with the induction of type 2 cytokines such as IL-13. IL-33 mRNA levels are extremely high in the CNS, and CNS glia possess both subunits of the IL-33R, yet whether IL-33 is produced by and affects CNS glia has not been studied. Here, we demonstrate that pathogen-associated molecular patterns (PAMPs) significantly increase IL-33 mRNA and protein expression in CNS glia. Interestingly, IL-33 was localized to the nucleus of astrocytes. Further, CNS glial and astrocyte-enriched cultures treated with a PAMP followed by an ATP pulse had significantly higher levels of supernatant IL-1beta and IL-33 than cultures receiving any single treatment (PAMP or ATP). Supernatants from PAMP + ATP-treated glia induced the secretion of IL-6, IL-13, and MCP-1 from the MC/9 mast cell line in a manner similar to exogenous recombinant IL-33. Further, IL-33 levels and activity were increased in the brains of mice infected with the neurotropic virus Theiler's murine encephalomyelitis virus. IL-33 also had direct effects on CNS glia, as IL-33 induced various innate immune effectors in CNS glia, and this induction was greatly amplified by IL-33-stimulated mast cells. In conclusion, these results implicate IL-33-producing astrocytes as a potentially critical regulator of innate immune responses in the CNS.