CD48 (SLAMF2) is an adhesion and costimulatory molecule constitutively expressed on hematopoietic cells. Polymorphisms in CD48 have been linked to susceptibility to multiple sclerosis (MS), and altered expression of the structurally related protein CD58 (LFA-3) is associated with disease remission in MS. We examined CD48 expression and function in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. We found that a subpopulation of CD4⁺ T cells highly upregulated CD48 expression during EAE and were enriched for pathogenic CD4⁺ T cells. These CD48⁺⁺CD4⁺ T cells were predominantly CD44⁺ and Ki67⁺, included producers of IL-17A, GM-CSF, and IFN-γ, and were most of the CD4⁺ T cells in the CNS. Administration of anti-CD48 mAb during EAE attenuated clinical disease, limited accumulation of lymphocytes in the CNS, and reduced the number of pathogenic cytokine-secreting CD4⁺ T cells in the spleen at early time points. These therapeutic effects required CD48 expression on CD4⁺ T cells but not on APCs. Additionally, the effects of anti-CD48 were partially dependent on FcγRs, as anti-CD48 did not ameliorate EAE or reduce the number of cytokine-producing effector CD4⁺ T cells in Fcεr1γ^-/- mice or in wild-type mice receiving anti-CD16/CD32 mAb. Our data suggest that anti-CD48 mAb exerts its therapeutic effects by both limiting CD4⁺ T cell proliferation and preferentially eliminating pathogenic CD48⁺⁺CD4⁺ T cells during EAE. Our findings indicate that high CD48 expression is a feature of pathogenic CD4⁺ T cells during EAE and point to CD48 as a potential target for immunotherapy.

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