Increased Langerhans cells and related cells in mesenteric lymph nodes of DNCB-sensitive mice.

We used electron microscopy to study mesenteric lymph nodes (LNs) of 2,4-dinitro-1-chlorobenzene(DNCB)-sensitive mice. It was found that Langerhans cells (LCs) and cells containing Birbeck-granule-like structures (BgSs) increased in number only after challenge with DNCB. This increase reached a peak 4 h after challenge. LCs and BgS cells were only found in the paracortical area of LNs. There were no appreciable differences in the morphology of LCs, BgS cells, and interdigitating reticulum cells (IDCs), except for the presence or absence of Bgs or BgSs. No LCs, BgS cells, or IDCs were found in the marginal sinus of mesenteric LNs or in the surroundings of afferent blood vessels. These findings were in complete agreement with those obtained in our previous study of cutaneous LNs. From our findings and the results of previously published studies, we propose the following conclusions: first, LCs and BgS cells observed in mesenteric LNs are the product of the differentiation and maturation of precursor cells pre-existing in the paracortical area of LNs caused by DNCB stimulation. Second, the activated T lymphocyte to DNCB pre-exists in the paracortical area; thus, the DNCB used for challenge stimulates this T lymphocyte to release lymphokine, which then causes some precursor cells to differentiation into LCs and/or BgS cells. Finally, morphological findings suggest that precursor cells of LCs and BgS cells are probably IDCs.