Serum-dependent adhesion and cytotoxicity of cells to Litomosoides carinii microfilariae

SERA from infected or immunised hosts have been reported to promote adhesion of leukocytes from those hosts to a variety of parasitic helminths ^1-5. Higashi and Chowdhury⁶ found selective adhesion of eosinophils to the infective larvae of Wuchereria bancrofti in the presence of serum from filariasis patients showing microfilaraemia, lymphoe-dema or elephantiasis. In albino rats infected with the filarial parasite Litomosoides carinii a termination of microfilaraemia (onset of latent infection) is associated with the adhesion of cells to microfilariae in the pleural cavity where the adult worms reside. Cells which seem morphologically to include macrophages, lymphocytes and polymorphs can be seen attached to living as well as to disintegrating microfilariae⁷. Virtually no attachment is seen during the patent stage of the infection. Furthermore, immunosuppression of rats with latent infection by means of cortisone, cyclophosphamide anti-lymphocyte serum or whole-body irradiation can lead to the appearance of microfilaraemia in the animals^7-9. Because the observations suggest the occurrence of an immune reaction, perhaps cell mediated, against microfilariae we investigated the mechanism of cellular adhesion. The results reported here show that adhesion in vitro is mediated by a serum factor and is accompanied by a cytotoxic effect on microfilariae.