Virus-associated immune activation causes rapid disruption of Peyer’s patches. (A) Mice were infected with VSV, and 2 or 5 days later, all macroscopically detectable Peyer’s patches were isolated. The total cell count for all Peyer’s patches per mouse was determined. (B-D) Mice were treated twice (days 0 and 3) with poly(I:C), and organs were examined 48 hours after the second injection. (B) Number of macroscopically detectable Peyer’s patches per mouse. (C) Mean number of cells in lymphoid compartments per mouse. (A-C) Each data point represents 1 individual mouse, and the mean of at least n = 4 mice per group is depicted as a bar. All data are representative of at least 2 independent experiments. (D) Hematoxylin and eosin–stained paraffin sections of the small intestine from 1 untreated and 1 poly(I:C)-treated mouse. The boxes indicate the Peyer’s patches depicted below with ×40 magnification. These sections are representative of n = 3 mice per group. i.p., intraperitoneally.