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Presentation of B-Crystallin to T Cells in Active Multiple Sclerosis Lesions: An Early Event Following Inflammatory Demyelination¹

Jeffrey J. Bajramovi^*, Arianne C. Plomp^*, Annette van der Goes, Cindy Koevoets^*, Jia Newcombe, M. Louise Cuzner and Johannes M. van Noort^2,*

^* Division of Immunological and Infectious Diseases, TNO Prevention and Health, Leiden, The Netherlands; Department of Cell Biology and Immunology, Faculty of Medicine, Free University, Amsterdam, The Netherlands; and Department of Neurochemistry, Institute of Neurology, University College London, London, United Kingdom

In the development of multiple sclerosis (MS), (re)activation of infiltrating T cells by myelin-derived Ags is considered to be a crucial step. Previously, B-crystallin has been shown to be an important myelin Ag to human T cells. Since B-crystallin is an intracellular heat shock protein, the question arises at what stage, if any, during lesional development in MS this Ag becomes available for CD4⁺ T cells. In 3 of 10 active MS lesions, B-crystallin could be detected inside phagocytic vesicles of perivascular macrophages, colocalizing with myelin basic protein and myelin oligodendrocyte glycoprotein (MOG). Although the detectability of MOG in phagosomes is considered as a marker for very recent demyelination, MOG was detected in more macrophages and in more lesions than B-crystallin. The disappearance of B-crystallin from macrophages even before MOG was confirmed by in vitro studies; within 6 h after myelin-uptake B-crystallin disappears from the phagosomes. B-Crystallin-containing macrophages colocalized with infiltrating T cells and they were characterized by expression of MHC class II, CD40, and CD80. To examine functional presentation of myelin Ags to T cells, purified macrophages were pulsed in vitro with whole myelin membranes. These macrophages activated both myelin-primed and B-crystallin-primed T cells in terms of proliferation and IFN- secretion. In addition, B-crystallin-pulsed macrophages activated myelin-primed T cells to the same extent as myelin-pulsed macrophages, whereas myelin basic protein-pulsed macrophages triggered no response at all. These data indicate that, in active MS lesions, B-crystallin is available for functional presentation to T cells early during inflammatory demyelination.