Characterization of dendritic cell subsets based on experssionof the C-type lectin receptor DCAL2

C-type Lectin Receptors (CLRs) on DCs play important roles in immunity and are expressed selectively on certain DC subsets. Murine DC-associated lectin 2 (DCAL2/MICL/Clec12a) is a type-II CLR with an ITIM. Using a mouse DCAL2-specific mAb, we found that DCAL2 is expressed at relatively high levels on APCs. DCAL2 was identified to be approximately 37kD in size and the tyrosine residues within the cytoplasmic tail of DCAL2 can be phosphorylated. Detectable levels of SHP-1 and PI3K associated with DCAL2 were observed, suggesting that DCAL2 may regulate signaling in APCs. DCAL2 can be rapidly internalized upon mAb ligation, suggesting a potential role in antigen processing and presentation. Therefore, we developed an scFv-Ag system to target Ags to DCAL2+ cells in vivo. Unexpectedly, targeting antigen to DCAL2 with scFv-Ags did not induce CD4 or CD8 T cell proliferation. Instead, it suppressed the expression of peptide/MHC-II complex expression when we targeted DCAL2 + cells using αDCAL2:HEL. Thus, targeting DCAL2 has a potential to regulate adaptive immune responses. DCAL2 expression could also be used to divide CD8α– DCs into DCAL2+DCIR2 – and DCAL2– DCIR2+ subpopulations. CD8α–DCAL2+ DC, CD8α –DC1R2+ DC and CD8α+DCAL2 + DC subsets each express different levels of TLRs and respond to unique classes of TLR ligands by producing distinct sets of cytokines. Whereas CD8α–DCAL2+ DCs robustly produce several cytokines including IL-12 in response to CpG, CD8α– DCIR2+ DCs produce only the cytokines TNFα and IL-10 in modest amounts when stimulated with zymosan. However, CD8α –DCIR2+ DCs, unlike the other DC subsets, strongly upregulate OX4OL expression when stimulated with bacterial flagellin. As predicted from their expression of cytokines, CD8α–DCAL2 + DCs efficiently induced Th1 responses in the presence of CpG both in vitro and in vivo, while CD8α– DCIR2+ DCs induced Th2 cells in response to flagellin. Thus, CD8α–DCAL2+ DCs, which have not been previously characterized, comprise a distinct CD8α– DC subset capable of supporting Th1 responses. DCAL2 is a useful marker to identify a Th1-inducing CD8α– DC population.