Importantly, the high virus load leads to functional inactivation of CD4+ T cells. selleck chemical The functional inactivation of CD4+ T cells is most likely a result of continued triggering by high viral load in combination with other parameters such as inflammatory cytokines, and expression of inhibitory receptors or pro-apoptotic molecules [14]. This is a relevant limitation of the CD8+ T cell-depletion experiments, and therefore a role of CD4+ T cells in the induction of immunopathology during LCMV-infection cannot be excluded. Here, we studied the role of CD4+ T cells in the destruction of splenic architecture and hepatic damage during LCMV infection. To restore CD4+ T cell function, CD8-depleted BL/6 mice were adoptively transferred with LCMV-immune CD4+ T cells or LCMV-GP61-specific T cell receptor transgenic (SMARTA [15]) CD4+ T cells.

We found that functional CD4+ T cells selectively destroy the splenic marginal zone, reduce protective LCMV-neutralizing antibodies and exert liver cell damage. Therefore, our results define an important role of CD4+ T cells in the induction of immunopathology in spleen and liver after LCMV infection. Results Adoptive transfer of LCMV-specific CD4+ T cells to CD8+ T cell-depleted mice rescues CD4+ T cell function in LCMV infection BL/6 mice clear LCMV-WE doses of up to 106 pfu within two weeks after infection below the detection limit of conventional plaque forming assays [16]. Control of LCMV is primarily mediated by cytotoxic CD8+ T cells and depletion of CD8+ T cells leads to high viremia until antibodies are mounted approximately 40 days after infection [13].

To analyze the function of LCMV-specific CD4+ T cells in the absence of CD8+ T cells and high viremia, BL/6 mice were depleted of CD8+ T cells by monoclonal antibody and infected with LCMV. As shown previously [13], CD8+ T cell depletion resulted in a drastic reduction of the relative and absolute number of LCMV-specific CD4+ T cells producing IFN�� and TNF�� on day 8 and 11 after infection (Fig. 1A,B). For example on day 11, the mean percentage of CD4+ T cell producing IFN�� after restimulation with GP61 decreased significantly from 0.63% to 0.05% and the mean absolute number of IFN��-producing CD4+ T cells dropped significantly from 0.65��105 to 0.085��105. Figure 1 Model to study LCMV-specific CD4+ T cell responses in the absence of CD8+ T cells.

In order to obtain functional LCMV-specific CD4+ T cells in CD8-depleted BL/6 mice, the following experiment was performed: First, Cilengitide na?ve BL/6 mice were depleted of CD8+ T cells by monoclonal antibody. On the same day, splenocytes of LCMV-infected BL/6 mice (17 days post infection) were harvested, purified for CD4+ T cells by MACS and adoptively transferred i.v. to these na?ve CD8-depleted BL/6 mice. Each mouse received 1.5��107 purified CD4+ T cells, which contained about 2.