SUSCEPTIBILITY DIFFERENCES TO CRYPTOSPORIDIUM-PARVUM INFECTION IN 2 STRAINS OF GAMMA-INTERFERON KNOCKOUT MICE

Differences in susceptibility to cryptosporidial infections were inves tigated between 2 strains of gamma interferon knockout (GKO) mice. Mal e C57BL/6J-Ifg(tml@) and BALB/c-Ifg(tml@) (GKO) mice, ages 8-10 wk, we re inoculated with infectious oocysts at various doses. C57BL/6J-Ifg(t ml@) mice developed overwhelming infections and died 9-12 days after i nfection. Low inoculum doses (1 x 10(3)) did not increase the survival time significantly. The infection intensity in C57BL/6J-Ifg(tml@) mic e inoculated with 1 x 10(5) oocysts/mouse increased markedly on day 4 postinfection (PI) and continued to increase significantly over the ne xt 6-7 days. Most of the C57BW6J-Ifg(tml@) mice exceeded 15% weight lo ss and died by day 10 PI. In contrast, BALB/c-Ifg(tml@) mice developed moderate infections from which they recovered. The average parasite l oad in the BALB/c-Ifg(tml@) mice was 100 times lower than in C57BL/6J- Ifg(tml@) mice. Mice survived until termination of the experiment (39 days) even when 1 x 10(6) oocysts per mouse were used for inoculation. BALB/c-Ifg(tml@) mice did not exhibit significant weight loss (or dif ference in stool consistency). These 2 mouse strains make excellent mo dels for studying differences in recovering and nonrecovering immune m echanisms.