Ultrastructural evidence for eosinophil-parasite adherence (EPA) reaction in human onchocercal lymphadenitis in the early period following diethylcarbamazine treatment.

Specimens of lymph nodes from eight patients with onchocerciasis after treatment with diethylcarbamazine (DEC) were studied by electron microscopy. The sequence of events during the eosinophil-parasite adherence (EPA) reaction in human onchocercal lymphadenitis was similar to that in EPA reaction described in in vitro models. The majority of microfilariae showed severe degeneration. Eosinophils adhered to the microfilariae forming an exact template of their surface. Not seldom, the surface of microfilariae or part of it was covered with electron dense material containing several well preserved cores of eosinophil granules. Large vacuoles containing eosinophil granules developed also in vivo. Some vacuoles disclosed granules with preserved morphology, others revealed altered granules. In addition to the mature granules in the vacuoles also small type eosinophilic granules were observed. The intracytoplasmic granules showed a variety of morphologic alterations too (partial solubilization of granule content with preserved crystalloid; crystalloid material was dissolved within the matrix, etc.). Sometimes, around the granules tubulo-vesicular structures were observed. This study suggested that, in contrast to in vitro experiments, immunologically mediated necrosis of eosinophils with subsequent release of granules was the most important way of eosinophil-mediated cytotoxicity in vivo.