Cellular and humoral peritoneal immunity to Mesocestoides vogae metacestode infection in mice.BACKGROUND
 Here, Mesocestoides (M.) vogae infection in mice is proposed as a suitable experimental model for studying the immunity in the peritoneal cavity of mice.


 To investigate the kinetics of immune parameters in M. vogae-infected mice, we detected, using flow cytometry, the expression of selected lymphoid and myeloid markers within the peritoneal cell population at day 0, 3, 6, 10, 14, 19, 25, 30 and 35 post-infection.  Then, using ELISA, we analyzed the cytokine IFN-γ, TGF-β, IL-4 and IL-10 responses and the levels of anti-M.  Cells isolated from the peritoneal cavity were subjected to further molecular analysis.  To assess cell activation, peritoneal cells were exposed to LPS, and culture supernatants were collected and assayed for the level of cytokines and production of nitrite.  Ly6C+ and Ly6G+ cells were isolated using MACS from the peritoneal cells at day 35 post-infection.  Both MACS-isolated subsets were co-cultured with preactivated T cells to measure their suppressive capacity.  Next, the role of parasite excretory-secretory antigens in induction of CD11b+ myeloid cells with the suppressive phenotype and the production of IL-10 was examined.


 In the peritoneal cavity an initial increase of CD11b+Gr-1+F4/80highMHC IIhigh cells, NK, NKT cells and CD8+ cytotoxic T cells was observed in the first week of infection.  At day 14 post-infection, an increase in the number of myeloid CD11b+Gr-1+ cells was detected, and most of this cell population expressed low levels of F4/80 and MHC II in later stages of infection, suggesting the impairment of antigen-presenting cell functions, probably through the excretory-secretory molecules.  Moreover, we confirmed that peritoneal Gr1+ cells (Ly6C+ and Ly6G+ population) are phenotypically and functionally consistent with myeloid-derived suppressor cells.  Metacestode infection elicited high levels of IL-10 and upregulated STAT-3 in peritoneal cells.  A higher level of IgM suggests that this isotype may be predominant and is involved in the host protection.


 CONCLUSIONS
 Mesocestoides vogae tetrathyridia induced the recruitment of immunosuppressive cell subsets, which may play a key role in the downregulation of immune response in long-term parasitic diseases, and excretory-secretory antigens seem to be the main regulatory factor.
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