Figure 2.

GC and PALS focus responses in the spleens of Msh2-deficient mice at day 8 after immunization. Mice were immunized with NP-CGG, and spleens were taken at 8 d after immunization and sectioned for immunohistochemistry, all as described in Materials and Methods. Parallel sections were stained either with (A) PNA (red) and NP (blue), or with (B) PNA (blue) and a polyclonal anti-IgG reagent (red). Notice the intense antigen- and IgG-specific staining at the edges of the white pulp in the +/+ spleen sections, characteristic of the PALS AFC focus response. This reaction is obviously reduced in +/− spleens and nearly absent in −/− spleens. At day 8 of the response, reduction in the number of GCs in Msh2 −/− mice has not occurred, but at day 12, when the PALS focus response has waned, there are twofold fewer GCs in −/− compared with +/+ spleens, and the average size of these GCs is much smaller (see Table I).