Ivermectin influence on the mast cell activity in nodules of onchocerciasis patients

Onchocercal nodules were stained immunohistochemically using antibodies spe cific for human mast cells and IgE to elucidate the localization and freque ncy of mast cells after a single oral dose of 150 mu g/kg ivermectin. Trypt ase-and chymase-positive mast cells occurred predominantly in mixed inflamm atory infiltrates and perivascularly, and never adhered to adult worms or m icrofilariae. Up to three days after ivermectin, mast cells and IgE-positiv e cells were markedly increased in the capsular area of nodules containing female worms with embryos and microfilariae compared to untreated nodules. In the centre of these nodules, around the adult Onchocerca volvulus, we fo und many tryptase-positive cells. More mast cells were IgE-positive than in untreated nodules, equalling the number of tryptase-positive mast cells. T here was a clear correlation between the appearance of mast cells and the a ttacks on damaged microfilariae by eosinophils and macrophages and in the v icinity of adult worms by neutrophils that occur soon after ivermectin trea tment. Onchocercomata harbouring female worms with oocytes only revealed, a fter all treatment intervals, the same mast cell numbers as untreated nodul es. In conclusion,during the first three days after administration, ivermec tin produces increased numbers of mast cells in nodules harbouring females with embryos and microfilariae, probably as part of an allergic reaction to the attacked microfilariae. Four to 19 days after ivermectin the number of mast cells in the entire nodule is no longer elevated.