In mice at 4 days after X-ray-irradiation at 0.5 Gy/min for 16 min, the tissue weights of immune organs, i.e., thymus and spleen, were decreased due to injury to lymphocytes by the X-rays. The resulting immunosuppressive condition allowed the growth of lactobacilli, i.e., L. murinus, which contained LacβTH-DG and possessed the ability to induce transcription of the fucosyltransferase gene for synthesis of FGA1. LacβTH-DG was detected in the jejunal and ileal contents of X-ray-irradiated mice, but not in those of control mice, whereas LacTetH-DG of L. johnsonii was present in the stomach and caecal contents of both mice. The amounts of FGA1 in the duodenal and jejunal tissues of X-ray-irradiated mice increased to 4- and 9-fold of those in controls, respectively. Reflecting the enhanced fucosylation of GA1, the total amounts of FGA1 excreted into the contents of X-ray-irradiated mice were 1.4-times higher than those in controls. Also, when the extent of enhanced fucosylation of GA1 in several regions of the digestive tracts of X-ray-irradiated mice was compared with that in immune deficient nude, scid and pIgR(-/-) mice, the more than 4-fold increases of FGA1 observed in duodenal and jejunal tissues corresponded to those in pIgR(-/-) mice without secretory IgA. Since an increased amount of FGA1 in the small intestine was observed only 4 days after X-ray-irradiation, and diminished synthesis of FGA1 occurred on administration of penicillin and streptomycin, fucosylation of GA1 in the small intestine was revealed to occur quickly in response to a change in the intestinal bacterial population.
Keywords: Bacterial glycolipid; Digestive tract; Fucosyl GA1; Intestinal bacteria; TLC-immunostaining.