Flt3-ITD alters the cell surface phenotype of splenic cDCs.
To characterize how constitutive Flt3 signaling impacts cDC function, cell surface levels of classical DC markers were investigated. Integrins or adhesion molecules (CD11c, CD11b, CD103, CD24), phenotypic molecules (CD8), inhibitory receptors (signal-regulatory protein α, SIRPα), MHC molecules (MHC I and II), costimulatory molecules (CD86, CD80, CD40 and CD24), co-inhibitory molecules (PD-L1), chemokine receptors (XCR1) and endocytic receptors (DEC205, Clec9A, Clec12A) were analyzed (Figure 3, Supplementary Figure 3 ). Significantly increased surface expression of MHC I, MHC II, CD103 was observed on most Flt3ITD/ITD cDC subsets. This was accompanied by lower CD11c, CD8, Clec9A, DEC205 and PD-L1 and varied expression of Clec12A. While Flt3+/+ cDC2 do not express Clec12A, it was detected at the surface of Flt3ITD/ITD cDC2. Confirming genetic profiling of Flt3+/+ NC cDC1s (26), these cells had reduced surface CD103, DEC205 and CD86, in addition to reduced Clec9A, MHC II and CD40 in comparison to other Flt3+/+ cDC subsets.