The precise antimicrobial mechanisms that are exerted by B cells from cell lines or primary cells are not yet well known. To date, among the possible antimicrobial mechanisms, nitric oxide (NO) is believed to be responsible for the control of pathogen growth by B cells. The B1 subset of B lymphocytes constitutively expresses the mRNA of inducible nitric oxide synthase (iNOS) and produces NO prior to and during Cryptococcus neoformans infection, which contributes to the elimination of the pathogen . The B1 cells also produce NO under TLR stimulation, which suggests that these cells have a role in non-specific, cell-mediated immunity
against pathogens . Novel recent evidence suggests BB-94 that B cells may also produce defensins in response to TLR stimulation. For example, the stimulation of B cells with CpG-DNA induces the production of β-defensin 2 . The scarcity of
evidence on the B cell mechanisms that are involved in Necrostatin-1 supplier the destruction of pathogens and on the precise role of B cells in the innate and specific response against mycobacterial infection makes this an interesting field of research. Conclusions In this manuscript, we describe the events that occurred during the internalisation of three different bacteria into a B VX-680 nmr lymphoblast cell line (Raji cell line). M. smegmatis, M. tuberculosis and S. typhimurium were readily internalised by Raji B cells as early as 1 h post-infection, and their uptake was inhibited in the presence of amiloride. During mycobacteria and Salmonella uptake, the B cells formed lamellipodia, ruffling and filopodia. After uptake, many spacious vacuoles or macropinosomes of different sizes were observed. The fluid-phase uptake that occurs during Salmonella or mycobacteria internalisation was abolished by amiloride, cytochalasin D or wortmannin, which confirms the involvement of the cytoskeleton during the internalisation, the participation of PI-3K, and the triggering of macropinocytosis during bacterial uptake. Death mycobacteria did not induce fluid-phase uptake in B cells. The secreted products in a M. tuberculosis and M. smegmatis culture Florfenicol were able to induce the same level of fluid-phase uptake as the live bacteria,
and the supernatant-induced fluid-phase uptake was inhibited by all of the inhibitors, which indicates that the soluble factors that are produced by these bacteria are able to induce macropinocytosis. The B cell cytoskeleton underwent crucial rearrangements during bacterial internalisation, which signifies that the cytoskeleton plays a role during macropinocytosis. M. smegmatis and S. typhimurium were eliminated by the Raji B cells; however, M. tuberculosis was able to survive and multiply in these cells, which suggests that the induction of macropinocytosis does not warrant bacterial elimination or survival. Acknowledgements This work was supported by CONACYT (project SEP-2004-C01) and SIP/IPN (projects 20121279 and 20121160). BEGP, JLH and EGL received fellowships from COFAA and EDI.