Alterations in blood eosinophil morphology, binding capacity for complexed IgG and kinetics in patients with tropical (filarial) eosinophilia.

As the significance of the eosinophilia which is found in some patients with chronic filarial infections is unknown, blood eosinophils were studied in seven patients with tropical (filarial) eosinophilia who had blood eosinophil counts between 5.2 and 56.6 x 10(9)/l. In six of these patients over 20% of the eosinophils were vacuolated, and degranulated eosinophils were found in the three patients with the most severe illness. In four patients serum eosinophil cationic protein levels were raised, and serial studies in two showed that they returned to normal after treatment with diethylcarbamazine. In addition, an increased proportion of eosinophils in these patients were able to bind to complexed IgG suggesting that they were responding to stimuli in the blood, and in one patient the blood eosinophil half-time clearance was prolonged. Labelled cells were cleared into the spleen, liver and bone marrow. These findings support the hypothesis that in patients with tropical (filarial) eosinophilia, blood eosinophils are induced to release their granule constituents into the circulation. It is suggested that these secretion products may interact with microfilariae, and may give rise to some of the clinical features of chronic filarial infections.