Antigenic competition in contact sensitivity. Evidence for changes in dendritic cell migration and antigen handling.

The frequency and antigen-bearing characteristics of dendritic cells (DC) within draining lymph nodes have been examined during antigenic competition in contact sensitivity. Pre-exposure of mice to oxazolone on the flank resulted in a marked depression of subsequent fluorescein isothiocyanate (FITC)-induced lymph node cell (LNC) proliferation. Antigenic competition was associated with an increased frequency of DC in the draining lymph nodes, but also with a reduced amount of antigen per cell. Thus, at 24 hr the draining nodes of FITC-challenged mice previously exposed to oxazolone exhibited an increased number of DC compared with control animals. Flow cytometric analysis revealed, however, that the percentage of antigen-bearing DC was reduced and that the median amount of antigen borne by DC was lower. Since exposure to oxazolone caused a significant increase in the frequency of DC in distant nodes, the changes observed in antigenic competition may, at least in part, be attributable to systemic effects on DC migration following application of the first antigen. These data indicate that the reduced primary proliferative response which characterizes antigenic competition in contact sensitivity is associated with, and may result from, induced changes in dendritic cell behaviour.