Kinetics of immunological responses, resistance to reinfection, and pathological reactions to infection with Trichinella spiralis.

Changes in immune responses, resistance to reinfection, and pathological reactions were studied serially in mice that had been infected for four to 40 weeks with 150 larvae of Trichinella spiralis. Immediate footpad hypersensitivity reactions to antigens of Trichinella were present throughout the period of observation. Delayed hypersensitivity reactions 48 hr after injection of antigen were first seen in mice infected for 14 weeks and gradually increased in size thereafter. Intestinal adult worm burdens were determined one week after challenge with 5000 larvae. There was resistance to reinfection and accelerated expulsion of worms in animals challenged three weeks after the primary infection; this resistance waned at seven and 13 weeks but reappeared in mice infected for 20 weeks or longer. Counts of larvae in muscle were determined four weeks after challenge with 5000 larvae. Marked resistance was present four weeks after the primary infection and was maintained for the duration of the study.