Abstract
Viable newborn larvae were used in several related series of experiments dealing with acquired immunity in rats. In the first study, newborn larvae were tested for their ability to induce immunity. It was shown that rats infected iv with newborn larvae had a 95% reduction in the number of muscle larvae deposited from an oral challenge infection as compared with noninjected controls. Freezethaw-killed newborn larvae were not effective in inducing acquired immunity. In the second study, the effects of acquired immunity on the ability of the newborn larva to reach the muscle, become encysted, and develop to a mature muscle larva were tested. It was found that immune rats were unable to prevent the normal course of development from occurring when newborn larvae were used as the challenge infection. These two studies, together with other evidence, lend strong support for the argument that functional antigens are found only in those stages of trichinella which possess a stichosome. The immunogenicity of the enteral phases of Trichinella spiralis has been demonstrated by several independent studies (Chipman, 1957; Campbell, 1965; Denham, 1966). However, the migrating newborn larva has not been studied for its immunogenic properties. This has largely been due to an inability to obtain pure preparations of this stage in large numbers. Recently Dennis et al. (1970) developed collection techniques which overcome this obstacle. The present studies were aimed at answering two questions: (1) Can newborn larvae induce acquired immunity? (2) Does acquired immunity prevent the encystment and development of the migrating newborn larva? It will be shown that the newborn larva is able to induce a strong acquired immunity and that this immunity is solely dependent upon the presence of living larvae. Further, it will be demonstrated that although immune rats are able to cause a reduction in the number of larvae reaching the muscle during an oral challenge infection, they are unable to prevent the migration, encystment, and normal development of larvae once they have reached the circulation. MATERIALS AND METHODS Newborn larvae were obtained, free of adults, by methods described by Dennis et al. (1970). Received for publication 2 July 1970. * This work was supported, in part, by NIH Postdoctoral fellowship L-F2-A1-31, 188, and USPHS Grant A1-04842. t Present address: Medical College of Ohio at Toledo, Toledo, Ohio 43614. Isolated larvae were washed, concentrated, then diluted in Hank's Balanced Salt Solution (Grand Island Biological Co., Grand Island, New York 14072). Each rat received 0.2 ml of larvae via the tail vein with the aid of a 1-ml tuberculin syringe fitted with a 26-gauge needle. Larvae were suspended by a vortex mixer before removal of each injection dose. Immunization of rats was accomplished by implanting a diffusion chamber (Millipore Filter Corporation, Bedford, Massachusetts) filled with 200 to 300 viable muscle larvae ip into each animal (Despommier and Wostmann, 1968). Muscle larvae were isolated from infected CFW male mice via peptic digestion for 1 hr at 37 C. These larvae were then suspended in a spinner flask (Belco Biological Glassware and Equipment, Vineland, New Jersey) containing a 2% gelatin0.6% nutrient broth solution. Muscle larvae were given orally to rats with the aid of a 1-ml tuberculin syringe fitted with an 18-gauge blunted needle. Muscle larvae were enumerated from each rat by methods described by Larsh and Kent (1949). The data were analyzed by Student's t test for statistical significance (Snedecor, 1959).
Published Version
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