Fig. 4.

Germ-free mice lack firmly adherent colonic mucus, but this mucus layer is restored by bacterial products. A and B: thickness of the adherent mucus in the colon in NMRI mice housed conventionally (n = 9) or under germ-free conditions (n = 11) either with luminal saline or the bacterial products LPS (conventional; n = 5, germ-free; n = 7) or peptidoglycan (PGN; conventional; n = 4, germ-free; n = 4). The mucus thickness is expressed in μm; *P < 0.05. C and D: representative histological samples from a conventional and a germ-free mouse stained with PAS solution. Arrows point at PAS-stained mucins. Bars correspond to 100 μm.