Local popliteal lymph node reactions to hexachlorobenzene and pentachlorobenzene: comparison with systemic effects

The effects of the presumed autoimmunogenic chemical hexachlorobenzene (HCB), and the closely related non-autoimmunogenic pentachlorobenzene (PCB) in the local popliteal lymph node assay (PLNA) were investigated. To that end 1-5 mg of HCB, equimolar amounts of PCB or the vehicle only, were injected into the hind footpads of rats or mice, and the reaction in the draining lymph node was evaluated on days 7 and 21 after injection. PLN were isolated, weighed, and cell suspensions were prepared to determine PLN cell numbers, and antibody production of PLN cells with an ELISPOT assay or a line immunoassay. The extent of the lymphoproliferative effect was examined by detection of proliferating cells with the BrdU method, and by measurement of paracortex and follicle areas, by combined immunohistochemistry and morphometry of PLN cryosections. We demonstrate here that HCB elevated PLN weights and cell numbers of the rat PLN, by day 7 after injection, but no elevation of antibody production in the PLN. Moreover, HCB caused an enlargement of both the PLN paracortical and follicular areas, and an elevation of proliferating paracortical T cells. None of the HCB-induced effects were found on day 21. HCB caused the same effects in the mouse PLNA, but they tended to sustain at least until day 21. Hardly any of the HCB-induced changes were found when PCB was injected. Previously, we have shown that oral exposure of Wistar rats to HCB elevated the number of splenic T cells and B cells, but also the serum levels of (auto-)antibodies and the production of these antibodies in the spleen, which is thus only partly in accordance with the results of the local reaction to HCB described in this study. This seeming contradiction is discussed.