The networks of fibroblastic reticular cells (FRCs, gp38+desmin+), representing stromal cells of the T cell zone, were less reticular in LCMV-infected BL/6 mice. In contrast, in CD8-depleted BIBW2992 BL/6 mice, B cell regions including FDC networks were preserved, while T cell regions including FRC networks were still partially disrupted. Interestingly, adoptive transfer of LCMV-immune CD4+ T cells to CD8-depleted BL/6 mice did not lead to a further disorganization of B and T cell regions including FDC and FRC networks when compared to CD8-depleted mice. Figure 3 Immunofluorescence analysis of B and T cell regions. In a next experiment, the expression of the chemokines CXCL13, CCL19, and CCL21 was analyzed by quantitative PCR in the spleen (Fig. 3B).

These chemokines are produced by FDCs and FRCs and are important for B and T zone compartmentalization [3]. LCMV-infected BL/6 mice showed a vigorous reduction of chemokine expression 11 days after infection [11], which was less pronounced in CD8-depleted mice [17]. Importantly, CD8-depleted mice receiving LCMV-immune CD4+ T cells did not show a statistically significant difference of chemokine levels to CD8-depleted mice. In accordance, immunofluorescence microscopy analysis of CXCL13 and CCL21 protein expression showed a strong reduction in LCMV infected BL/6 mice (Fig. S1). Both chemokines were less reduced in CD8-depleted mice without a clear difference to CD8-depleted mice receiving LCMV-immune CD4+ T cells.

Taken together, these experiments revealed that the adoptive transfer of CD4+ T cells to CD8-depleted mice neither contributed to a substantial destruction of the splenic white pulp nor to a reduction of CCL19, CCL21, and CXCL13 expression. Destruction of the splenic marginal zone by CD4+ T cells Under the same experimental conditions, the integrity of the splenic marginal zone was analyzed by immunohistochemical staining of ER-TR9+ marginal zone macrophages (MZM) and MOMA-1+ (CD169+) marginal zone metallophilic macrophages (MOMA). The splenic marginal zone was largely destroyed in immunocompetent BL/6 mice 11 days after LCMV infection with reduced numbers of MZM and MOMA (Fig. 4A,B). In contrast, CD8-depleted BL/6 mice retained the marginal zone with numbers of MZM and MOMA comparable to na?ve BL/6 mice (Fig. 4A,B).

Interestingly, adoptive transfer of LCMV-immune CD4+ T cells to CD8-depleted BL/6 mice destroyed the marginal zone with reduced numbers of MZM and MOMA, comparable to LCMV-infected control BL/6 mice GSK-3 (Fig. 4A,B). Therefore, CD4+ T cells destroy lymphoid architecture in the absence of CD8+ T cells and their effect is focused to the marginal zone of the spleen. Figure 4 Immunohistochemistry analysis of the marginal zone. Analysis of B cell subtypes We next wanted to define the effect of LCMV-specific CD4+ T cells on defined B cell subsets in the spleen. As described by Allman et al [18] and shown in Fig.