Fig. 3
Naive B cells can be activated directly in lung tissue. A Experimental setup for the analysis of early B-cell activation in the lung. The mice received a single dose of 5 µg of LPS intranasally, which increased the frequency of endogenous B cells in the lung from approximately 0.8 to 2.2%. Three days later, antigen-specific T and B cells (the latter sorted for CD62Lhigh cells) were adoptively transferred, and the mice were immunized i.n. with antigen and LPS as adjuvants the next day. One group was injected with FTY720 i.p. at the time of antigen application and 12 h later. B Antigen-specific B cells (shown as the frequency of total B cells) in lung and lung-draining lymph nodes on day 0 and day 1, with and without FTY720 (FTY) treatment. C Expression of IgD and CD69 on antigen-specific B cells on day 0 and day 1. Vascular lymphocytes were excluded from analysis by i.v. injection of antibodies against CD3 and B220 immediately before sacrifice. Flow cytometry plots display one representative animal. D For analysis on day 3, the LPS pretreatment was omitted. One group received FTY720 at the time of antigen application and 24 and 48 h later. E Frequencies of antigen-specific B cells and the expression of IgD and CD69. The bar graphs show pooled data from two independent experiments with seven/eight animals per group B, C or from one representative experiment out of two E. Each animal is depicted by a dot, and the bar graphs indicate the means. ns, p ≥ 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001
