Selective enrichment of T_h1 CD45RB^low CD4⁺ T cells in autoimmune infiltrates in experimental allergic encephalomyelitis

Abstract

The cytokine effector status of CD4+ T cells from lymph nodes (LN) and the central nervous system (CNS) of SJL/J mice immunized with autoantlgen in adjuvant for the induction of experimental allergic encephalomyelitis (EAE) was compared. CD4+ T cells were FACS sorted based on the levels of expression of the activation marker CD45RB. Low levels of expression of this surface marker are induced by antigen recognition and are associated with ‘effector’ T cell function. Reverse transcriptase polymerase chain reaction (PCR) was used to analyze the expression of different T cell cytokine genes in the sorted populations. CD45RBlow cells constituted a minority of CD4+ cells in the LN and expressed elevated levels of IL-2, IFN-γ, and IL-4 mRNA, whereas the CD45RBhigh CD4+ population did not express detectable message for these cytokines under linear PCR conditions. By contrast to the LN, CD4+ cells from the CNS were predominantly CD45RBlow and expressed readily detectable levels of IL-2 and IFN-γ mRNA, but almost no IL-4 transcription could be detected. IL-4 mRNA levels in CNS were 100- to 250-fold lower than in LN. Also, IL-4 message could not be detected in the CNS 1 week after remission. A cytokine-speclflc Immunocytochemical single cell staining technique was used to enumerate cytoklne-produclng cells in LN cell populations and in CNS infiltrates. Between 1 and 5% cells in Isolated LN cells produced detectable IL-2 and IFN-γ. By contrast, the frequency of cytoklne-produclng cells stained in pertvascular infiltrates in frozen sections from the brains of animals with active EAE was 10-fold higher. The frequency of cytokine-produdng cells correlated closely with that of CD45RBlow-expresslng cells in both the LN and the infiltrated brain. Our results confirm the functional significance of the CD45RB phenotype and indicate an enrichment of Th1 cells in the CNS, which suggests an active selection process in the activation/accumulation of antigen-specific T cells at the site of inflammation.