Skin Reactions in Sensitized, Infected and Normal Rabbits with Filarial and other Nematode Antigens

Rabbits were sensitized with saline extracts of A scarfs and the filarial worms, Dirofilaria immitis and Litomosoides carinii, and by infection with Trichinella spiralis. When these rabbits were tested intracutaneously, the different antigens reacted specifically, and there was no significant reactions with filaria antigen in the Ascaris sensitized rabbits. However, in the trichinous rabbits all the antigens reacted strongly, although Trichinella antigen was negative in the heterologously sensitized rabbits. There was evidence of reaction by Ascaris in a few of the non-Ascaris-sensitized animals. This may have been due to specific sensitization by obscure ascarid infections. It is suggested that these anomalous reactions, occurring with antigens prepared from the different adult worms, may actually have been demonstrations in vivo of a reaction between host tissue antigens (derived from the intestines of the nematodes used) and the natural tissue antibody of the host (rabbit). The phenomenon was especially marked in trichinous rabbits, in which muscle degeneration was general. Extracts of D. immitis precipitated fractionally with ethanol or ammonium sulphate yielded effective skin-test antigens. Those with ammonium sulphate had a less irritant effect. The yield of carbohydrate was small. There is some evidence that the female extract was irritating. The carbohydrate fraction of Ascaris failed to react in low dilution. It is concluded that in skin tests for filariasis, cross reactions with intestinal helminths such as Ascaris do not ordinarily occur.