Weill Cornell Medical College Brooklyn, NY, United States
Mir Howlader1, Audrey Baeyens2, Susan Schwab2 and theresa Lu3, 1Weill Cornell Medical College, Brooklyn, NY, 2New York University Grossman School of Medicine, New York, NY, 3Hospital for Special Surgery, New York, NY
Background/Purpose: T cell entry into and exit from lymph nodes (LNs) exposes T cells to antigens/cytokines required for their activation and regulates the nature of the T cell immune response. However, T cell trafficking through lymphoid tissues in SLE has not been explored. Impaired T cell exit means prolonged exposure to antigen-presenting cells which may lead to increased production of autoantibodies and contribute to disease pathogenesis. Lymphopenia and lymphadenopathy in SLE suggests that there is a disruption in lymphocyte trafficking where lymphocytes are being kept out of circulation and potentially being held in LNs. Egress of T cells from LNs is carefully regulated by the LN microenvironment. A low sphingosine-1-phosphate (S1P) concentration in the LN maintains S1P receptor 1 (S1PR1) expression on T cells which promotes egress by overriding CCR7/CCL21 retention signals. Here, we hypothesize that the LN microenvironment is altered in SLE and contributes to impaired egress of T cells. In this study, we investigate egress of T cells and then delineate a potential mechanism behind changes to egress in SLE.
Methods: We used an inducible lupus mouse model (B6 IMQ) where mice receive topical applications of imiquimod, a TLR7 agonist that produces a high Type 1 interferon signature also present in SLE. To determine if the LN microenvironment affects egress, CFSE labeled naive T cells were intravenously (i.v) injected into the B6 IMQ mice. Egress was assessed by comparing the number of T cells remaining in a LN after blocking their entry with anti-L-selectin to their numbers pre-blockade. S1PR1 expression was used as a readout of S1P levels as S1PR1 is internalized in the presence of high S1P. CD69 can also internalize S1PR1 through physical association and to assess for this, T cells from CD69 knock-out (KO) mice were injected i.v into B6 IMQ. Flow cytometry was performed on skin draining LNs to identify cells and compare expression levels of relevant receptors and cytokines.
Results: Egress of CFSE labeled T cells was significantly impaired in B6 IMQ mice relative to healthy controls. T cell S1PR1 expression was downregulated, suggesting that there is a high S1P level in the LN. Egress of CD69 KO T cells was also impaired and their S1PR1 expression was downregulated, further supporting that high S1P levels lead to the S1PR1 downregulation. CCL21+ fibroblast reticular cells (FRCs) significantly increased in B6 IMQ LNs, suggesting they are also acting as retention signals.
Conclusion: Here our results suggest two changes in the LN microenvironment, an increase in S1P levels and expansion of CCl21+ FRCs, that can promote increased retention of T cells. Current directions are focused on understanding what regulates these changes and what their impact on T cell phenotype is. As impaired egress of T cells can potentially contribute to disease pathogenesis, understanding what regulates T cell exit may potentially open a new area of therapeutic advancement in SLE.
Disclosures: M. Howlader, None; A. Baeyens, None; S. Schwab, None; t. Lu, None.
