In Situ Tolerance within the Central Nervous System as a Mechanism for Preventing Autoimmunity

Brabb, Thea; von Dassow, Peter; Ordonez, Nadia; Schnabel, Bryan; Duke, Blythe; Goverman, Joan

In our analyses of T cell phenotype, we also examined the expression of CD62L, an LN homing receptor typically expressed on naive T cells (26, 27) . In the periphery of both nontransgenic and TCR transgenic mice, CD62L was predominantly expressed on naive T cells (defined by expression of CD44, CD49d, or CD45RB) as expected. Surprisingly, in nontransgenic and TCR transgenic models, CD62L expression was observed on CNS T cells that exhibited activation/memory markers as well as on naive T cells, and did not correlate with either phenotype. CNS lymphocytes were enriched for CD62L low cells compared with splenocytes in nontransgenic animals (CNS, 47 Ϯ 7%; spleen, 10 Ϯ 7%; n ϭ 3), Rag Ϫ/Ϫ MBP TCR2 transgenic mice (CNS, 46 Ϯ 11%; spleen, 7 Ϯ 2%; n ϭ 3), Rag Ϫ/Ϫ Ova transgenic mice (CNS, 64 Ϯ 10%; spleen, 10 Ϯ 1%; n ϭ 4), and Rag Ϫ/Ϫ LCMV transgenic mice (CNS, 52 Ϯ 17%; spleen, 9 Ϯ 4%; n ϭ 3). This general enrichment of CD62L low cells in the CNS and lack of correlation with expression of activation markers suggest that CD62L is not strictly a naive T cell marker, and its downregulation in some cases may occur independently of T cell activation.