Factor XIIIa positive dendritic cells are a major accessory cell population in the elicitation phase of DNCB-induced contact hypersensitivity

The phenotypes and distribution of accessory cells in the ear skin of lambs during the elicitation phase of dinitrochlorobenzene (DNCB)-induced contact hypersensitivity (CHS) were examined using indirect immunoperoxidase histochemistry (ABC method), and a panel of antibodies. Thirty lambs, between 21 and 26 weeks of age, were divided into groups of 10. The shaved right ear of one group was treated with DNCB. Two weeks later this group was challenged with DNCB. One group was treated with the vehicle alone and the remaining group was left untreated. The lambs were slaughtered 48 h after challenge, and tissue specimens were collected from the ears of the three groups. Factor XIIIa+ (FXIIIa+) cells were prominent in the superficial dermis and showed predominantly a perivascular and subepidermal distribution. The other markers were less prominent, and whereas CD1+ cells and CD68+ cells showed a reaction pattern similar to the FXIIIa+ cells, CD14+ cells were found scattered predominantly in the deep dermis. There appeared to be an increase in FXIIIa+ cells, CD1+ cells, and CD68+ cells in the dermis of the DNCB-treated lambs 48 h after challenge. Only CD1+ cells were detected in epidermis of normal controls, and these cells appeared to be decreased in number in the two treated groups. Computer-assisted morphometric analysis was used to estimate the relative presence of the accessory cell subpopulations in the superficial and deep dermis and the entire dermis. A statistical analysis of the relative area of immunostaining showed a significantly increased presence of FXIIIa+ cells and CD68+ cells in the dermis of the DNCB-treated lambs 48 h after challenge. Interestingly, FXIIIa+ cells and CD68+ cells were also significantly increased in the vehicle treated group compared with untreated controls. We found no significant difference in the presence of CD1+ cells or CD14+ cells in the DNCB treated group compared with the controls. The study showed that FXIIIa+ DDC are the major accessory cell population in normal ear skin of lambs and the major responsive population during the elicitation phase of CHS. The lack of response in the CD1+ cell population suggests a less prominent role for the LC-related DC in the skin during the elicitation phase.