T–B interactions yield CD3 + B cells and CD20 + T cells with pathogenic features in multiple sclerosis
Selia Baier, Zhongyi Wang, Nathalie Loll, Simone Mader, Stephan Winklmeier, Fady Shenouda, Samantha Ho, Eva Oswald, Selen Ünlü, Arek Kendirli, Atay Vural, Ceren Özdemir, Christoph A. Reichel, Jan Kranich, Jan Schmidt, Julie Boisclair, Rachel Cuttat, Walter Georgescu, Yoann Gilbart, Magali Jivkov, Ulrike Naumann, Eddie A. James, José M. Carballido, Tania Kümpfel, Valérie Dubost, Philippe Couttet, Edgar MeinlClassically, B and T cells are differentiated by their mutually exclusive expression of surface markers such as CD3 and CD20, but it is now established that a few percent of T cells in human blood display also CD20. We analyzed CD3 + CD20 + cells in detail by combining single-cell proteogenomics, FACS, and ImageStream. Thereby, we identified CD3 + B cells and found that about 40% of plasmablasts displayed CD3 in both blood and tonsils. In tonsils, where T–B interactions occur, about 80% of follicular helper T (T fh ) cells displayed CD20. In vitro, coactivation of T and B cells induced marker exchange via trogocytosis. We refer to the resulting cells as “masquerading” lymphocytes and analyzed them in multiple sclerosis (MS). CD20 + T cells were markedly enriched in cerebrospinal fluid, exhibited cytotoxic gene signatures, accumulated in perivascular inflammatory cuffs, and showed increased myelin antigen reactivity. Anti-CD20 therapy (ofatumumab) not only depleted masquerading lymphocytes but also prevented their reinduction. Together, we identify CD3 + B cells as footprints of T–B interactions thereby shifting the paradigm of lymphocyte-specific surface markers and implicate masquerading lymphocytes as active contributors to MS immunopathology.