Stage-specific protective immunity to microfilariae of Litomosoides carinii in Mastomys natalensis.

Abstract

Experiments were performed to know whether immunity to microfilariae (mf) is effective to the protection against infection with infective larvae (L3) of Litomosoides carinii in Mastomys natalensis. Animals were immunized subcutaneously with 5×105 live mf at two week intervals for six times. Mf in peripheral blood were detected on the following day of subcutaneous inoculation, and mf density increased gradually during five weeks. The mf density in the blood began to decline from five weeks and four of 8 animals became amicrofilaremic after six weeks. Immunofluorescence revealed that these immunized individuals developed antibodies not only against mf but also against both L3 and adult worms. Beginning at 11 weeks after initiation of immunization, animals received the challenge infection with L3, and the protective effect induced by mf immunization was examined by the worm recovery three and 14 weeks after challenge infection. There was no suppressive effect of immunization with live mf to the challenge infection as determined by recoveries of developing and adult worms. These results indicated that protective immunity induced by mf immunization was stage-specific and not effective against L3 to adult stage worms of L. carinii in M. natalensis.