Decreased Recovery of Invading Parasites from the Lungs as a Parameter of Acquired Immunity to Schistosomiasis in the Mouse

Abstract

After a challenge exposure to Schistosoma mansoni, fewer schistosomula are recovered from the lungs of laboratory mice that have had a previous infection than from the lungs of animals that have had no previous contact with the parasite. The number of organisms recovered from the lungs after challenge decreases in two separate stages of the primary infection. The first stage (one to four weeks after primary exposure) reflects a delay in the migration of the parasite rather than protective immunity. The second stage (which begins several weeks after the appearance of fully developed adult schistosomes) correlates with immunity to reinfection. The results indicate that, when resistant mice are challenged, a significant percentage of the invading schistosomula is eliminated in the lungs or at an earlier point in the pathway of migration. For this reason, recovery from the lungs may prove a valid and convenient assay for analysis of the immunologic basis of acquired resistance to schistosome infections.