FMS-like tyrosine kinase 3 ligand (FLT3L) administration alters rat classical and plasmacytoid dendritic cell phenotype in a tissue-specific manner

Abstract Background: Characterization of tissue-resident dendritic cell (DC) subsets, including classical DCs (cDCs) and plasmacytoid DCs (pDCs), is complicated experimentally by their rare nature. Many investigators have artificially increased DC yields through administration of the cytokine FMS-like tyrosine kinase 3 ligand (FLT3L). Despite its previous use experimentally, no study has yet described the effects of in vivo FLT3L administration on rat tissue-resident DCs. This study provides an advanced characterization of rat tissue-resident cDCs and pDCs following FLT3L injection. Methods: Lewis rats were injected once daily for 10 days with PBS vehicle or with 10, 50, or 100μg of FLT3L. Animals were sacrificed on the 11th day and dissected to obtain liver, spleen, and mesenteric lymph nodes. Cells were stained for 13-color flow cytometry and data was acquired on the Cytek Aurora spectral cytometer. Results: cDC and pDC enumeration increased in a dose-dependent manner following FLT3L administration. Expression levels of MHC I, MHC II, CD40, CD80, CD86, and PD-L1 were evaluated on liver, spleen, and mesenteric lymph node-resident cells. MHC II, CD80, and CD86 levels were significantly decreased on liver-resident cDCs but remained unchanged or increased on spleen and lymph node cDCs. Changes in MHC I/II and costimulatory molecule expression levels on pDCs varied by tissue and marker. Conclusions: FLT3L administration in vivo increased cDC and pDC enumeration, generated immature cDCs in the liver, and increased cDC maturation in the spleen and mesenteric lymph nodes. This comprehensive characterization of rat liver, spleen, and lymph node-resident DCs is key to understanding the effects of FLT3L on cDC and pDC phenotype.