B-cell receptor reactivity against Rothia mucilaginosa in nodular lymphocyte-predominant Hodgkin lymphoma.

Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is a Hodgkin lymphoma expressing functional B-cell receptors (BCRs). Recently, we described a dual stimulation model of IgD+ lymphocyte-predominant (LP) cells by Moraxella catarrhalis antigen RpoC and its superantigen MID/hag, associated with extralong CDR3s and HLA-DRB1*04 or HLA-DRB1*07 haplotype. Aim of the present study was to extend the antigen screening to further bacteria and viruses. Fabs of 7 new and 15 previously reported cases were analyzed. The reactivity of non-Moraxella spp.-reactive Fabs against lysates of Rothia mucilaginosa was observed in 5/22 (22.7%) cases. Galactofuranosyl transferase (Gltf) and 2,3-butanediol dehydrogenase (Bdh) of R. mucilaginosa were identified by comparative silver-and immunostaining in two-dimensional gels, with subsequent mass spectrometry and validation by Western blots and ELISA. Both R. mucilaginosa Gltf and Bdh induced BCR pathway activation and proliferation in vitro. Apoptosis was induced by recombinant Gltf/ETA'- immunotoxin conjugates in DEV cells expressing recombinant R. mucilaginosa-reactive BCRs. Reactivity against M. catarrhalis RpoC was confirmed in 3/7 newly expressed BCRs (total 10/22 reactive to Moraxella spp.), resulting in 15/22 (68.2%) cases with BCR reactivity against defined bacterial antigens. These findings strengthen the hypothesis of bacterial trigger contributing to subsets of NLPHL.