Murine antigen-induced inflammation--a model for studying induction, resolution and the adaptive phase of inflammation.

Murine zymosan-induced peritonitis is the model most frequently used to study resolution of inflammation. However, the antigen-induced peritonitis model may be better suited for studying resolution of inflammation and the adaptive phase that follows. The objective of this study was to provide an evaluation of the kinetics of cells and mediators during induction, resolution and the adaptive immune phases of a murine antigen-induced inflammation. Female C57BL/6 mice were immunized twice subcutaneously with mBSA and three weeks after the initial immunization they were injected intraperitoneally (i.p.) with mBSA, which induced peritonitis. Peritoneal cells were counted and expression of surface molecules and chemokine receptors analyzed with flow cytometry. Chemokine and cytokine concentrations in peritoneal fluid were determined by ELISA. Two neutrophil populations, differing in size and granularity and slightly in expression of surface molecules, were observed in the peritoneal cavity after induction of inflammation. Macrophages disappeared from the peritoneal cavity following i.p. administration of mBSA but appeared again as they differentiated from recruited monocytes and peaked in numbers at 48 h. At that time point, two distinct populations of macrophages were present in the peritoneal cavity; one with high expression of F4/80, also expressing the atypical chemokine receptor D6 as well as CCR7; the other expressing low levels of F4/80 and also expressing CD11c and CD138. Eosinophils appeared in the peritoneum 3h following i.p. administration of mBSA and peaked at 48 h. At that time point they had upregulated their expression of CCR3 but decreased their expression of CD11b. Peritoneal levels of CCL11 peaked at 6h and may have led to recruitment of the eosinophils. NK cells and T cells peaked at 48 h, whereas B cells peaked at 5 days, with the majority being B1 cells. Peritoneal concentrations of pro-inflammatory cytokines (IL-ß and IL-6) and chemokines (CCL2 and CCL3) peaked at 3h, whereas IL-1ra peaked at 6h, sTNF-R at 24h and sIL-6R and TGF-ß at 48 h. The results show kinetic alterations in cell populations and mediators in a murine model that may be an excellent model to study initiation and resolution of inflammation and the following adaptive phase.

Dietary omega-3 fatty acids enhance the B1 but not the B2 cell immune response in mice with antigen-induced peritonitis.

The effects of omega-3 fatty acids on the adaptive immune response have mainly been analysed in vitro with varying results. How omega-3 fatty acids affect the adaptive immune response in vivo is largely unknown. This study examined the effects of dietary fish oil on the adaptive immune response in antigen-induced inflammation in mice, focusing on its effects on B cells and B cell subsets. Mice were fed a control diet with or without 2.8% fish oil, immunized twice with methylated BSA (mBSA) and peritonitis induced by intraperitoneal injection of mBSA. Serum, spleen and peritoneal exudate were collected prior to and at different time points after induction of peritonitis. Serum levels of mBSA-specific antibodies were determined by ELISA and the number of peritoneal and splenic lymphocytes by flow cytometry. The levels of germinal center B cells and IgM(+), IgG(+) and CD138(+) cells in spleen were evaluated by immunoenzyme staining. Mice fed the fish oil diet had more peritoneal B1 cells, more IgM(+) cells in spleen and higher levels of serum mBSA-specific IgM antibodies compared with that in mice fed the control diet. However, dietary fish oil did not affect the number of peritoneal B2 cells, splenic IgG(+) or CD138(+) cells or serum levels of mBSA-specific IgG antibodies in mice with mBSA-induced peritonitis. These results indicate that dietary fish oil can enhance the adaptive immune response, specifically the B1 cell response, which may lead to better protection against secondary infection as well as improvement in reaching homeostasis following antigenic challenge.

Dietary fish oil reduces the acute inflammatory response and enhances resolution of antigen-induced peritonitis.

Dietary n-3 polyunsaturated fatty acids (PUFA) influence the inductive phase of inflammation but less is known about their effects on the resolution phase. This study examined the effects of dietary fish oil on induction and resolution of antigen-induced inflammation in mice. Mice were fed a control diet with or without 2.8% fish oil, immunized twice with methylated BSA (mBSA) and inflammation induced by intraperitoneal injection of mBSA. Prior to and at different time points after mBSA administration, peritoneal cells were analyzed and expression of surface molecules determined by flow cytometry. Concentration of chemokines, cytokines and soluble cytokine receptors was determined by ELISA. Mice fed the fish oil diet had fewer peritoneal neutrophils, shorter resolution interval and lower levels of pro-inflammatory cytokines and chemokines than mice fed the control diet. In mice fed the fish oil diet there was an early peak in peritoneal levels of the immunosuppressive molecules sIL-6R and TGF-ß, that was not seen in mice fed the control diet. In the resolution phase, peritoneal macrophages from mice fed the fish oil diet expressed more of the atypical chemokine receptor D6 and peritoneal TGF-ß levels were higher than that in mice fed the control diet. Furthermore, in the late-resolution phase there were more peritoneal eosinophils and macrophages in mice fed the fish oil diet than in mice fed the control diet. These results demonstrate a suppressive effect of n-3 PUFA on the inductive phase of inflammation and indicate an enhancing effect of n-3 PUFA on resolution of inflammation.