Interleukin-1 dose, mouse strain, and end point as they affect protection of mouse jejunum

Interleukin 1 (IL-1) has been shown to protect a number of normal tissues against radiation injury. In mouse jejunum, modest protection against radiation injury has been reported using only the in vivo crypt survival assay in one mouse strain. The major goal of this study was to determine the protective effect of IL-1 on mouse jejunum using two assays of damage, crypt cell survival and lethality from radiation-induced crypt cell depletion, in two mouse strains, C3Hf/Kam and BALB/c nu/+, which were bred and maintained in a specific-pathogen-free barrier colony. In addition, the dependence of protection on the IL-1 dose in both assays was determined. Our findings showed that IL-1 protection of crypt cell depletion and subsequent death of the animals from loss of these cells was dependent on the IL-1 dose. We found that the amount of protection by IL-1 was related to the criterion used to assess the protection. For example, if protection was determined as a ratio of D₁₀'s or LD(50/10), a bigger DMF was obtained for BALB/c mice than C3H mice with the same IL-1 dose, suggesting that C3H mice were not as well protected. However, if protection was determined by the increase in crypt cell number after IL-1, there was an identical 2.4-fold increase in crypt cells after the same IL-1 dose in both strains. On the basis of this criterion, then, protection of crypt cells by IL-1 did not depend on the mouse strain. Although the effect of IL-1 on animal survival at 10 days was strain dependent, the difference was related to differences in the slopes of the respective crypt cell survival curves for the two strains and not to different effects of IL-1 in the two strains tested.