Local Inactivation of Sphingosine 1-Phosphate in Lymph Nodes Induces Lymphopenia

Abstract

Sphingosine 1-phosphate (S1P) initiates T and B cell exit from lymphoid tissues by activating the S1P1 receptor on lymphocytes. To define the mechanistic details of this ligand–receptor interaction, the biological activity of the S1P-blocking Ab Sphingomab was investigated. Treatment of mice with Sphingomab resulted in blood B and T cell lymphopenia. Although Sphingomab blocked S1P1-mediated calcium flux and receptor downregulation by S1P in vitro, plasma from Sphingomab-treated mice demonstrated a 4-fold increase in S1P concentration and largely retained its stimulating activity on S1P receptors. Plasma-borne S1P was obviously not sufficiently inactivated by Sphingomab to account for the observed lymphopenia. Therefore, we addressed the local S1P-blocking activity of Sphingomab in spleen and peripheral lymph nodes (pLNs) as a potential cause of PBL depletion. Transwell chemotaxis assays revealed the migration of freshly isolated splenocytes, but not pLN cells to S1P. However, chemotaxis of pLN cells was regained after culture in S1P-low medium, and pLN cells isolated from Sphingomab-treated mice also revealed enhanced chemotaxis to S1P, indicating substantial local inactivation of S1P in pLN after Sphingomab treatment. We conclude that treatment with the S1P-blocking Ab Sphingomab induces lymphopenia by inactivating S1P locally in pLN and not systemically in plasma. Consequently, the presence of local S1P amounts in secondary lymphoid organs contributes to B and T cell egress.

Sphingosine 1-Phosphate in Blood: Function, Metabolism, and Fate

“…It is feasible to speculate that excess amounts of S1P associated with, but not bound to albumin, are rapidly filtered out by the liver [89], whereas S1P localized in RBC has to be maintained by regular S1P metabolism. In line with this hypothesis, application of an anti-S1P antibody resulted in increased S1P concentrations in plasma, which is caused by replacement of antibody-bound S1P with unbound S1P, both contributing to the total S1P concentration measured in plasma [14]. Co-culture experiments of RBC with endothelial cells also point to an S1P transportation based on tight RBC and endothelial cell contact, which may explain the observed differences between application of S1P associated either with albumin or with RBC [2].…”

“…A possible answer could be different receptor availability and/or signalling of S1P associated with serum albumin or lipoproteins [13]. Studies with the anti-S1P antibody Sphingomab demonstrated that antibody-captured S1P was replaced with S1P released from RBC within 24 h [14]. The S1P-concentration in plasma is therefore well-buffered by RBC, which should ensure quite stable values.…”

Impaired T-cell responses to sphingosine-1-phosphate in HIV-1 infected lymph nodes

“…In mice, freshly-isolated LN T cells are also typically unresponsive to S1P stimulation but regain responsiveness after a period of incubation in S1P-deprived medium. 42 It has been suggested that subnanomolar concentrations of S1P are found within lymphoid interstitial spaces, 40 and this may suffice to desensitize lymph node T cells to S1P during the isolation process. In our culture conditions, we did not measure S1P in culture supernatants; therefore, we cannot rule out the possibility that S1P may be present still within the medium during this incubation period.…”

Anaplasma phagocytophilum Dihydrolipoamide Dehydrogenase 1 Affects Host-Derived Immunopathology during Microbial Colonization

“…However, relative lymphopenia and circulating IFN-␥ levels displayed an inverse relationship to peripheral lymphocyte counts in mice infected with the A. phagocytophilum lpda1::TnHimar1 mutant. Quantitation of peripheral lymphocyte counts and lymphocyte populations in lymphoid tissues is complex, as lymphopenia can reflect total body lymphocyte depletion or lymphocyte sequestration in lymphoid tissues (19,54). Given the presence of marked splenomegaly with lymphoid hyperplasia in both groups of infected mice, it is likely that infectioninduced lymphopenia arose due to mechanisms such as lymphocyte sequestration and altered recirculation.…”