*Purpose: Lymph node (LN) stromal laminin α4 (Lama4) is associated with tolerance. We hypothesized that fibroblastic reticular cell (FRC) derived Lama4 contributes to a tolerogenic LN by regulating adaptive T cell immunity.

*Methods: We created an FRC Lama4 conditional knock out (KO) using the Pdgfrβ promoter to drive Cre-lox excision in FRCs. CD45.1⁺ splenocytes were adoptively transferred into CD45.2⁺ wild type (WT) and Lama4 KO recipients. C57BL/6 Lama4 KO and WT mice received BALB/c cardiac or lung allografts and were harvested after 3-4 days.

*Results: After adoptive cell transfer, fewer CD45.1⁺ cells, including CD4 and CD8 T cells, B cells, conventional dendritic cells (cDCs), plasmacytoid DCs (pDCs), and Foxp3^–GFP⁺ thymic Tregs migrated to Lama4 KO LNs compared to WT controls. Immunohistochemistry showed fewer transferred CD4 T cells and Tregs distributed in the cortical ridge (CR) and around the high endothelial venules (HEVs) of KO compared to WT LNs. After lung allografting, H&E staining showed the grafts in Lama4 KO recipients had more lymphocytic infiltration relative to WT, indicating more intense alloreactivity. After lung transplant, there were fewer Foxp3⁺ cells, pDCs and cDCs in the CR and around HEVs in KO peripheral LNs and lung draining LNs. After cardiac transplantation, the allografts in KO recipients also had greater lymphocytic infiltration, indicating more intense alloreactivity than WT. BALB/c hearts were transplanted into Lama4 KO recipients and treated with low dose immunosuppression. Tacrolimus treated Lama4 KO recipients had significantly shorter allograft survival (MST 11.5 days versus MST 18 days in WT, p<.002). Lama4 KO recipients receiving a single dose of anti-CD40L displayed a trend for decreased survival (MST 42.5 vs 60 days, p<0.01).

*Conclusions: Depletion of FRC LN Lama4 impaired immune cell homing to the LNs. FRC derived Lama4 is necessary for lymphocyte migration and retention in LNs, with a preferential effect on Tregs, which may regulate homeostasis and tolerance. In murine cardiac transplantation, KO recipients had more intense rejection histology, and tolerogenic immunosuppression was not effective without FRC-Lama4. After lung transplantation, FRC-Lama4 regulates the migration of DCs and Tregs in recipient LNs and affects graft rejection.

« Back to 2022 American Transplant Congress