In-situ localisation of immunocompetent cells in Fasciola hepatica infestation in rats and mice.

Abstract

Fasciola hepatica (Liver fluke) is primarily a parasite of cattle and sheep, although other animals may also become infested [I] . Cattle and rats have been found to develop partial resistance to re-infestation with Fasciola hepatica, sheep and mice however, develop no effective immune response and are susceptible to reinfestation [2]. Thus, rats and mice provide useful models for the disease in cattle and sheep respectively. The parasite burrows through the intestinal wall migrating through the liver on its way to the larger bilary passages, its site of chronic infestation and egg production. Therefore, a localisation of immunocompetent cells within the intestine of rats and mice following infestation with Fasciola hepatica was investigated. A prospective study was carried out in which groups of 5 mice and rats were infested with metacercariae from Fasciola hepatica, along with the same number of uninfested control siblings and sacrificed 21 days later. A further group of 5 rats were infested with metacercariae and on day 21 were rechallenged. These animals were sacrificed 72 hours post rechallenge. Intestinal cryostat sections were prepared and stained with monoclonal antibodies against CD8, CD4, CD3, and MHC class 11. In addition, histological mast cell staining of all groups was carried out using Astra blue. In the normal mouse, the majority of CD8' cells formed a characteristic pattern of what have been referred to as 'cords' or 'rows' of cells underlying the epithelium of the villi with occasional intraepithelial lymphocytes observed [3]. CD4' cells were predominately confined to the lamina propria. CD3' cells formed a pattern representative of combined CD4 and CD8 cell panerns. Mast cells were detected in the sub-mucosa and lamina propria in very low numbers. No obvious difference in number, intensity or location of any of these cell types was seen between infested and control mice. The particular monoclonal antibody used to detect mouse MHC class I1 failed to give reproducible immunohistochemical staining. In the normal rat, CD8' cells, although in the same location, were less numerous and did not form 'cords' as frequently as in mouse tissue. CD4' cells were predominately confined to the lamina propria, and numerous MHC class 11' cells were also located to this region. Mast cells were found in the submucosa and lamina propria in greater numbers than in mouse tissue. Primary infested rats showed no difference in CD8' cell numbers or distribution. However, as a group, MHC class I1 and CD4 cell staining was more intense in these animals than in controls, although no obvious difference in cell distribution patterns was observed. Mast cell numbers were considerably increased. In re-infested rats, the intensity of MHC class I1 and CD4 cell staining was consistently weaker than even the control groups, but mast cell numbers remained elevated. Once again, no difference was seen in the CD8' cell population. Lack of an effective immune response leading to susceptibility is reflected by the apparent similarity of cell numbers and staining intensity between controls and infested mice. The increased staining intensity of MHC class 11' and CD4' cells and increased mast cell numbers observed in primary infested rats may be indicative of an effective immune response in these animals.