Resistance toOnchocerca lienalismicrofilariae in mice conferred by egg antigens of homologous and heterologousOnchocercaspecies

Abstract

Embryonic stages of variousOnchocercaspecies have been used to stimulate resistance in CBA mice to challenge injections with the microfilariae ofOnchocerca lienalis. Comparable levels of resistance to challenge (29–37% reductions) were conferred by living, freeze-killed, or sonicated organisms administered with Freunds‘ Complete Adjuvant (FCA). Antigens extracted in saline, or with the detergent sodium deoxycholate, were also protective. Adjuvants enhanced the protective effect, particularly FCA (78% reduction), Freunds‘ Incomplete Adjuvant (74% reduction), aluminium hydroxide (70% reduction) andBordetella pertussis(70% reduction). Detergent extracts prepared from intact embryos withn-octyl glucoside also stimulated significant levels of protection against microfilarial challenge when given with FCA (37–45% reductions). Levels of resistance induced by immunizations with intact organisms were greatest following subcutaneous (s.c.) injection over the neck or by intramuscular inoculation. Soluble extracts were also particially effective given by s.c. inguinal or intraperitoneal injection. A time-interval of greater than 3 weeks between the completion of immunization and challenge was required for the expression of immunity. Cross-protection against challenge withO. lienalismicrofilariae was also afforded to mice by immunization with intact embryos or detergent extracts ofOnchocerca gutturosa(45 and 34% reductions),Onchocerca gibsoni(66 and 47% reductions) orOnchocerca volvulus(58 and 41% reductions). It is concluded that the embryonic stages of both human and animal parasites provide a source of cross-protective antigens of value in studies on resistance toOnchocercamicrofilariae in experimental hosts.