Objective      To observe the effect of ionizing radiation on the expression of mouse cryptdin 4 (Crp4) and explore the biological significance.        Methods      BALB/c mice (8 weeks old) were randomly divided into a control group (n=5) and a radiated group (n=15)

and the radiated group was treated by total-body ionizing radiation (8 Gy X-ray). The small intestinal tissue and eyeball blood were collected before and after ionizing radiation (at 9

24

and 72 h respectively). Immunohistochemical assay and Western blot analysis were employed to detect the alteration of Crp4 in mouse small intestine. Quantitative chromogenic tachypleus amebocyte lysate test was  used to analyze the alteration of lipopolysaccharide (LPS) in blood serum. Crp4 peptide was obtained through chemical synthesis. Colony counting was employed to assess the antibacterial activity of Crp4 against Escherichia coli

Enterococcus faecalis

Lactobacillus acidophilus

and Bifidobacterium bifidum. Also

the effect of Crp4 on the release of IL-1β from mouse RAW264.7 cells after LPS simulation was evaluated.        Results      The expression of Crp4 in the mouse small intestine was increased after ionizing radiation

and the alteration was the most remarkable at 72 h (P0.01). The serum LPS level of the radiated mice was significantly increased after 9 h (P0.05)

and peaked after 72 h (P0.01). Conditional pathogenic bacteria (Escherichia coli and Enterococcus faecalis) were more sensitive to Crp4 than probiotics (Lactobacillus acidophilus and Bifidobacterium bifidum). Moreover

it was found that Crp4 could decrease the release of IL-1β from RAW264.5 cells stimulated with LPS.       Conclusion      Ionizing radiation can induce the up-regulation of Crp4 expression

which might play an important role in the regulation of the intestinal flora and relieve of the inflammatory responses.