Killer (FASL regulatory) B cells are present during latent TB and are induced by BCG stimulation in participants with and without latent tuberculosis.

Regulatory B cells (Bregs) have been shown to be present during several disease states. The phenotype of the cells is not completely defined and the function of these cells differ between disease. The presence of FASL expressing (killer) B cells during latent and successfully treated TB disease have been shown but whether these cells are similar to regulatory B cells remain unclear. We assessed the receptor expression of FASL/IL5 (killer B cells), CD24/CD38 (regulatory B cells) on whole peripheral blood of participants with untreated active TB and healthy controls. We then isolated B cells from a second cohort of M.tb exposed (Quantiferon (QFN) positive) and unexposed (Quantiferon negative) HIV negative participants, and evaluated the frequency of killer B cells induced following stimulation with BCG and/or CD40 and IL5. Our data reveal no difference in the expression on CD24 and CD38 between participants with active TB and the controls. There was also no difference in the frequency of regulatory B cells measured in the peripheral blood mononuclear cells (PBMC) fraction between latent TB and uninfected controls. We did however notice that regulatory B cells (CD24hiCD38hi) population express the FASL receptor. The expression of killer B cell phenotype (CD178+IL5RA+) was significantly higher in controls compared to those with active TB disease (1,06% vs 0,455%). Furthermore, we found that BCG restimulation significantly induced the FASL/IL5RA B cells but this was only evident in the QFN positive group. Our data suggest that both regulatory and killer B cells are present during latent and active TB disease but that the frequency of these populations are increased during latent disease. We also show that the FASL+IL5RA+ B killer B cells are induced in latent TB infection following BCG restimulation but whether these cells are indicative of protection remains unclear.