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Sphingosine-1-phosphate (S1P) regulates the migration of follicular B cells
(B2 cells) and directs the positioning of Marginal zone B cells (MZ B cells) within the spleen. The
function of S1P signalling in the third B cell lineage, B1 B cells, mainly present in the pleural and
peritoneal cavity, has not yet been determined. Methods: S1P receptor expression was analysed
in peritoneal B cells by real-time polymerase chain reaction (qPCR). The chemotactic response to
S1P was studied in vitro. The role of S1P signalling was further explored in a s1p4
−/− mouse
strain. Results: Peritoneal B cells expressed considerable amounts of the S1P receptors 1 and 4
(S1P1 and S1P4, respectively). S1P1 showed differential expression between the distinct peritoneal B
cell lineages. While B2 cells showed no chemotactic response to S1P, B1 B cells showed a migration
response to S1P. s1p4
−/− mice displayed significant alterations in the composition of peritoneal
B cell populations, as well as a significant reduction of mucosal immunoglobulin A (IgA) in the
gut. Discussion: S1P signalling influences peritoneal B1 B cell migration. S1P4 deficiency alters the
composition of peritoneal B cell populations and reduces secretory IgA levels. These findings suggest
that S1P signalling may be a target to modulate B cell function in inflammatory intestinal pathologies.
Background: Gram-negative infections of the peritoneal cavity result in profound modifications of peritoneal B cell populations and induce the migration of peritoneal B cells to distant
secondary lymphoid organs. However, mechanisms controlling the egress of peritoneal B cells from
the peritoneal cavity and their subsequent trafficking remain incompletely understood. Sphingosine1-phosphate (S1P)-mediated signaling controls migratory processes in numerous immune cells. The
present work investigates the role of S1P-mediated signaling in peritoneal B cell trafficking under
inflammatory conditions. Methods: Differential S1P receptor expression after peritoneal B cell activation was assessed semi-quantitatively using RT-PCR in vitro. The functional implications of
differential S1P1 and S1P4 expression were assessed by transwell migration in vitro, by adoptive
peritoneal B cell transfer in a model of sterile lipopolysaccharide (LPS)-induced peritonitis and in
the polymicrobial colon ascendens stent peritonitis (CASP) model. Results: The two sphingosine-1-
phosphate receptors (S1PRs) expressed in peritoneal B cell subsets S1P1 and S1P4 are differentially
regulated upon stimulation with the TLR4 agonist LPS, but not upon PMA/ionomycin or B cell receptor (BCR) crosslinking. S1P4 deficiency affects both the trafficking of activated peritoneal B cells
to secondary lymphoid organs and the positioning of these cells within the functional compartments of the targeted organ. S1P4 deficiency in LPS-activated peritoneal B cells results in significantly reduced numbers of splenic innate response activator B cells. Conclusions: The S1P-S1PR system is implicated in the trafficking of LPS-activated peritoneal B cells. Given the protective role of peritoneal B1a B cells in peritoneal sepsis, further experiments to investigate the impact of S1P4 mediated signaling on the severity and mortality of peritoneal sepsis are warranted.