Non-pathogenic tissue-resident CD8+ T cells uniquely accumulate in the brains of lupus-prone mice.

Severe lupus often includes psychiatric and neurological sequelae, although the cellular contributors to CNS disease remain poorly defined. Using intravascular staining to discriminate tissue-localized from blood-borne cells, we find substantial accumulation of CD8+ T cells relative to other lymphocytes in brain tissue, which correlates with lupus disease and limited neuropathology. This is in contrast to all other affected organs, where infiltrating CD4+ cells are predominant. Brain-infiltrating CD8+ T cells represent an activated subset of those found in the periphery, having a resident-memory phenotype (CD69+CD122-PD1+CD44+CD62L-) and expressing adhesion molecules (VLA-4+LFA-1+) complementary to activated brain endothelium. Remarkably, infiltrating CD8+ T cells do not cause tissue damage in lupus-prone mice, as genetic ablation of these cells via β2 m deficiency does not reverse neuropathology, but exacerbates disease both in the brain and globally despite decreased serum IgG levels. Thus, lupus-associated inflammation disrupts the blood-brain barrier in a discriminating way biased in favor of non-pathogenic CD8+ T cells relative to other infiltrating leukocytes, perhaps preventing further tissue damage in such a sensitive organ.