The survival and function of IL-10-producing regulatory B cells are negatively controlled by SLAMF5

B cells have essential functions in multiple sclerosis and in its mouse model, experimental autoimmune encephalomyelitis, both as drivers and suppressors of the disease. The suppressive effects are driven by a regulatory B cell (Breg) population that functions, primarily but not exclusively, via the production of IL-10. However, the mechanisms modulating IL-10-producing Breg abundance are poorly understood. Here we identify SLAMF5 for controlling IL-10+ Breg maintenance and function. In EAE, the deficiency of SLAMF5 in B cells causes accumulation of IL10+ Bregs in the central nervous system and periphery. Blocking SLAMF5 in vitro induces both human and mouse IL-10-producing Breg cells and increases their survival with a concomitant increase of a transcription factor, c-Maf. Finally, in vivo SLAMF5 blocking in EAE elevates IL-10+ Breg levels and ameliorates disease severity. Our results suggest that SLAMF5 is a negative moderator of IL-10+ Breg cells, and may serve as a therapeutic target in MS and other autoimmune diseases.

The group size used for all experiments ensured statistical significance of the results. Each in vitro experiment was performed at least four times. Due the variability of EAE each of the in vivo experiments included a large cohort of mice. For charcterization of Multiple sclerosis patients experiments, group size was limited by the availability of patient samples. Sample size calculations were not performed In most experiments no data was excluded.
In few experiments outliers (3-fold or more from the mean of the group) were excluded. Experiments were samples were excluded: Fig.4 a, a bilogical repeat was removed from the experiment (same donor from both treatment groups). Fig. 2J,two biological repeats were ecxluded.
To verify the reproducibility, experiments were performed three to five times. Only the RNAseq experiment was preformed twice. Replication attempts were successfull Mice were randomly distributed amongst groups at the start of each experiment. For in vitro assays, cells were randomly assigned to either experiment or control groups. A biological sample was split into equall samples for control and experiment groups.
Blind scoring was done in the EAE mice model.
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No wild animals were involved
This study did not involve field collected samples All animal procedures were approved by the Animal Research Committee at the Weizmann Institute of Science Healthy donor samples -The study was performed on blood cells from healthy donors. For most healthy donors buffy coats were provided by the Blood Bank (MDA Israel Magen David Adom), no additional information (age, sex) was given for these donors. These samples were recived without details from the blood bank For Multiple Sclerosis patients: peripheal blood charcterization. Blood samples of newly diagnosed Multiple Sclerosis patients and matched (age/sex) controls were recieved from the department of Neurology, Barzilai University Medical Center, Israel.
Multiple Sclerosis samples:samples were collected from newly diagnosed patients that were not treated yet. Normal controls were sec/age matched accordingly.
Buffy coats for blood cell isolation from healthy blood donors were provided by the Blood Bank (MDA Israel Magen David Adom) Blood samples of newly diagnosed and yet to be treated Multiple Sclerosis patients and matched (age/sex) controls were recived. Recruitment occurred when patients came to the Centre for Rheumatology for their first treatment, and blood samples were taken before the treatment.

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