Some specializations of DCs for vaccine capture, MHC-peptide complex formation, and T cell stimulation. DCs express many adsorptive uptake receptors whose natural ligands are generally not yet known. For this reason, anti-receptor antibodies are often used experimentally as surrogate antigens. Several receptors are type II transmembrane proteins with a single external C-type lectin domain found on distinct DC subsets: DC-SIGN and the asialoglycoprotein receptor on monocyte-derived DCs, BDCA-2 on plasmacytoid cells, and Langerin on Langerhans cells. MMR and DEC-205 are type I proteins with eight to ten contiguous C-type lectin domains; these receptors can also be expressed on certain endothelia and epithelia. Other receptors, such as FcγR, are not DC-restricted but function selectively in DCs to mediate the exogenous pathway for presentation on MHC class I products. Beyond antigen capture, DCs (or particular DC subsets) express high levels of select TLRs and thereby mature in response to specific microbial stimuli. During maturation, DCs produce and export high levels of several costimulatory molecules for T cell growth and differentiation. DC maturation regulates many of the elements involved in antigen capture and processing.