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Studies on Microfilaremia in Dogs

II. Levels of Microfilaremia in Relation to Immunologic Responses of the Host^*

This portion of the studies on microfilaremia in dogs was concerned chiefly with the immunologic response of uninfected dogs to repeated injections of living microfilariae concentrated by a newly devised technique employing phytohemagglutinin. Immunity in these dogs was demonstrated by in vitro tests with living microfilariae, by passive transfer of their sera, and by the effects of the sera on the production of microfilariae by adult worms maintained in vitro. Uninfected dogs that received multiple immunizing inoculations of microfilariae tolerated no circulating microfilariae regardless of the size of the challenge inoculum. Sera taken from these dogs agglutinated homologous, living microfilariae, whereas no agglutination took place in sera from control dogs or from infected dogs with patent microfilaremia. Absorption tests indicated that these agglutinins were specific. The production of microfilariae was inhibited when such sera were incorporated in media used for the in vitro maintenance of adult worms. Furthermore, when serum from "immunized" dogs was injected intravenously into infected dogs, the levels of microfilaremia in the latter animals were significantly lowered. These observations suggest that the antibody demonstrated in vitro is also effective in vivo.

It was inferred from these results that a relationship exists between the levels of microfilaremia and the concentration of specific antibodies produced by the host in response to the presence of microfilariae, and that a high titer of such antibodies is probably responsible for the absence of a microfilaremia in some filarial diseases.

^* Supported by grants 2E-2 and AI-04919 from the National Institutes of Health, U. S. Public Health Service, and by the Office of the Surgeon General, Department of the Army (Commission on Parasitic Diseases, Armed Forces Epidemiological Board).