Rapid upregulation and differential expression of B7 occurs during the course of a primary type 2 in vivo immune response

Few studies have investigated the expression of costimulatory molecules on A PCs during an in vivo immune response (IR). B7-1 and B7-2 expression were examined in the mouse Peyer's patches (PP), mesenteric lymph node (MLN) and spleen 0, 1, 4, and S days after oral inoculation with the gastrointestinal nematode parasite, Heligmosomoides polygyrus, which induces a type 2 IR with elevated CD4⁺ T cell IL-4 production by day 8. Increases in PNA-stained cells and associated increases in B7-2 expression were evident as early as day 1 after II. polygyrus inoculation in the PP. By 4 days after inoculation immunohistological analysis revealed increased MLN B7-2 in discrete regions of the developing GC and follicular mantle, and throughout the T-cell rich zone, while with FACS increased MLN B cell B7-2 was not detected until day 8 after infection. In the spleen, increased B7-2 expression and GC formation were delayed until day 8 after H. polygyrus inoculation, as assessed by immunohistological analysis. Although surface B7-1 was readily detected in tissues of B7-1 transgenic mice, no B7-1 elevations were detected in either lymphoid tissues or spleen of normal mice during the primary mucosal IR to H. polygyrus.