Macrophages, myofibroblasts and mast cells in a rat liver infected with Capillaria hepatica

We trapped a rat (Rattus norvegicus) infected with Capillaria hepatica. At necropsy, grossly yellowish-white nodules (2-3 mm in diameter) were noted to be scattered on the liver's surface. Microscopically, granulomatous and fibrotic nodules that contained the eggs and/or adult worms of Capillaria hepatica were detected in the liver. Septal fibrosis was diffusely formed throughout the liver. There were a number of ED1-positive macrophages located in the sinusoids of the pseudolobules. On the double staining, myofibroblasts and mast cells were generally observed within the fibrous septa with the mast cells in close proximity to the myofibroblasts. We suggest that the interactions between macrophages, myofibroblasts and mast cells play a role in the septal fibrosis observed in rats infected by Capillaria hepatica.

Changes of cytokine mRNA expression and IgG responses in rats infected with Capillaria hepatica

The mRNA expression of several cytokines was evaluated in splenocytes and mesenteric lymph node (MLN) cells of rats infected with Capillaria hepatica by reverse-transcription (RT)-PCR until week 12 after infection. IgG1 and IgG2a, which are associated with Th1 and Th2 response, respectively, were also assessed by ELISA. The results indicated that the majority of cytokines, including the Th1 (IL-2 and IFN-gamma) and Th2 cytokines (IL-4, IL-5 and IL-10) were expressed at maximal levels during the early stage of infection (after week 1-2), and the ELISA data also evidenced a similar pattern of changes in IgG1 and IgG2a. Th1 and Th2 cytokines responded in a similar fashion in this rat model. The expression of cytokines in splenocytes was significantly higher than that in MLN cells, thereby indicating that cytokine production is controlled more by spleen than by MLN. In addition, the observation that IFN-gamma expression increased unexpectedly at the time of maximal egg production (6 weeks after infection) indicated that IFN-gamma is a cytokine reacting against egg production. However, increased IL-5 expression occurring in tandem with worm activity indicated that the activity of C. hepatica might be controlled by IL-5 expression.

Capillaria hepatica in rats: focal parasitic hepatic lesions and septal fibrosis run independent courses

Capillaria hepatica causes two main lesions in the liver of rats: multifocal chronic inflammation, directly related to the presence of disintegrating parasites and their eggs, and a process of systematized septal fibrosis. The comparative behavior of these two lesions was investigated in rats experimentally infected with 600 embryonated eggs, following either corticosteroid treatment or specific antigenic stimulation, in an attempt to understand the relationship between these two lesions, and the pathogenesis of septal fibrosis. The two treatments differently modified the morphological aspects of the focal parasitic-related lesions, but did not interfere with the presentation of diffuse septal fibrosis, although a mild decrease in the degree of fibrosis occurred in corticoid-treated animals. These findings indicate that although the two lesions are C. hepatica induced, they are under different pathogenetic control, the induction of septal fibrosis being triggered during early infection to follow an independent pathway.