Figure 4.

Germinal center B cells and protective antibody formation in surviving Sterne-infected A/J mice. A/J mice were orally gavaged with 10⁹ spores of the Sterne strain of Bacillus anthracis, and after 2 weeks after infection indicated organs were analyzed for germinal reactions. A, Frequency of B220⁺ immunoglobulin D (IgD)⁺ cells in the mesenteric lymph nodes (MLNs), Peyer's patches (PPs), and spleen. Left panel shows representative plots and compiled data from 3 independent experiments. B, Frequency of Fas⁺ and peanut agglutinin (PNA)⁺ cells of activated B cells (B220⁺IgD⁺). C, Sera collected at days 5 and 14 after infection were analyzed for their neutralization capacity. In vitro lethal toxin neutralization assay was performed using sera derived from Sterne-infected or uninfected mice. Data shown as mean ± standard error of the mean. **P < .01 and ***P < .0001, compared with untreated J774A.1 cells. Data represent observations from 3 independent experiments and are shown as mean ± standard error of the mean. ***P < .001, compared with the phosphate-buffered saline (PBS) group. Abbreviations: LT, lethal toxin; St, Sterne-infected sera (day 5); survivor, Sterne-infected sera (day 14).