DISTINCTION OF CLASS-II MHC(-LIKE INTERSTITIAL DENDRITIC ANTIGEN-PRESENTING CELLS IN MURINE DERMIS FROM DERMAL MACROPHAGES() LANGERHANS CELL)

Dermal cells are capable of initiating contact-hypersensitivity respon ses but the precise identification of the antigen-presenting cell with in murine dermis is lacking. Class II major histocompatibility complex (MHC)(+) cells with dendritic shape and lacking endothelial factor VI II but expressing the dendritic antigen-presenting cell marker NLDC-14 5 were observed in the perivascular and interstitial dermis of BALB/c and C3H/HeN skin. The heterogeneous class IZ MHC(+) cells could be div ided into two subsets: each was class II MHC+ CD45(+) (bone marrow der ived) GR-1(-) (nonneutrophil/macrophage) CD3(-) (non T), but one subse t was CD11b(+) (beta 2 integrin) and the other was CD11b(-). Ultrastru ctural examination of class II MHC+ cells revealed the presence of a L angerhans cell-like/indeterminant cell subset with indented nuclei, de ndritic morphology, active cytoplasm, and dense intermediate filaments . Phagolysomes and Birbeck granules were not observed in such cells, i ndicating these were distinct from dermal macrophages and from classic al epidermal Langerhans cells, respectively. Cells with a monocyte/mac rophage ultrastructural appearance were also noted, likely representin g the class II MHC subset expressing CD11b and Ly6c (monocyte/endothel ial antigen). Dermal cells in suspension were capable of processing an d presenting large protein antigens to antigen-specific T-cell hybrido mas; dermal cells also induced the syngeneic mixed lymphocyte reaction . The dermal antigen-presentation activities were totally abrogated by removal of class II MHC+ cells, but not by removal of CD11b(+) cells or Ly6c(+) cells, indicating that potent antigen-presenting cell activ ity was restricted to the class II MHC+ CD11b(-) Ly6c(-) subset (Lange rhans cell-like/indeterminant cells). In conclusion,within complex arr ay of dermal leukocytes a murine dermal class II MHC+ cell population expressing a Langerhans cell-like/dendritic antigen-presenting cell ph enotype and exhibiting potent antigen processing and presenting activi ty can be identified. The positioning of potent interstitial dendritic antigen-presenting cells at the interface of the vasculature with the dermal interstitium provides rapid access to an antigen-presenting ce ll as T cells first egress into the skin.