Direct demonstration of the infiltration of murine central nervous system by Pgp-1/CD44 high CD45RB low CD4 + T cells that induce experimental allergic encephalomyelitis

Abstract

In experimental allergic encephalomyelitis (EAE), autoimmune T cells infiltrate the central nervous system (CNS) and initiate demyelinating pathology. We have used flow cytometry to directly analyse the migration to the CNS of MBP-reactive CD4 + T cells labelled with a lipophilic fluorescent dye (PKH2), in SJL/J mice with passively transferred EAE. Labelled cells constituted about 45% of the CNS CD4 + population at the time of EAE onset. Almost all (>90%) of the PKH2-labelled CD4 + T cells from EAE CNS were blasts and were α/β T cell receptor (TCR) +, CD44(Pgp-1) high, and the majority were CD45RB low. By contrast, most PKH2-labelled CD4 + T cells in lymph nodes, although CD44 high, were CD45RB high cells. The cells that were transferred to induce EAE were essentially similar to antigen-primed lymph node cell populations, containing less than 15% CD44 high cells, and most of them were CD45RB high. The CD44 high CD45RB low phenotype is characteristic of memory/effector T cells that have been activated by antigen recognition. The difference in CD45RB expression between CNS and LN could therefore reflect differential exposure and/or response to antigen. Consistent with this, PKH2-labelled CD4 + cells isolated from the CNS were responsive to MBP in vitro, whereas PKH2 + CD4 + cells from lymph nodes showed almost undetectable responses. In control experiments in which ovalbumin (OVA)-reactive T cells were transferred, a small number of fluorescent-labelled CD4 + T cells were also detected in CNS, but there were very few blasts, and these remained CD45RB high. These results argue for induction of the memory/effector phenotype of CD4 + cells, their selective retention in the CNS, as a consequence of antigen recognition.