Experimental pulmonary schistosomiasis: lack of morphological evidence of modulation in schistosomal pulmonary granulomas

Abstract

Numerous pulmonary schistosome egg granulomas were present in mice submitted to partial portal vein ligation (Warren's model). The granulomas were characterized by cellular aggregations formed within alveolar tissue. Main cellular types were macrophages (epithelioid cells), eosinophils, plasma cells and lymphocytes. These cells were supported by scanty fibrous stroma and exhibited close membrane contact points amongst themselves, but without forming specialized adhesion apparatus. When granulomas involved arterial structures, proliferation of cndothelial and smooth muscle cells occurred and fibrosis associated with angiogenesis became more evident. Granulomas formed around mature eggs in the pulmonary alveolar tissue presented approximately the same size and morphology regardless of the time of infection, the latter being 10, 18 and 25 weeks after cercarial exposure. This persistence of morphological appearance suggests that pulmonary granulomas do not undergo immunological modulation, as is the case with the granulomas in the liver and, to a lesser extent, in the intestines. Probably, besides general immunological factors, local (stromal) factors play an important role in schistosomal granuloma modulation.

Histopathological and Immunohistochemical Study of Lambs Experimentally Infected with Fasciola hepatica and Schistosoma bovis

“…In addition to general immunological factors which play an important role in schistosomal granuloma modulation (Souza-Vidal et al, 1993) and the inverse relationship between antibody level and granuloma size observed in mice (Hirata et al, 1993), the different morphological appearance of S. bovis egg granulomas in both organs examined in this study supports a local immunological response. Fibrous granulomas and eggs without appreciable cellular reactivity observed mainly in liver and intestine of group S/F could be due to the duration of infection with S. bovis in this group (30 weeks) in comparison to group S (24 weeks) and they could also represent old granulomas and immunological tolerance to the parasite, respectively.…”

Schistosomes in the Lung: Immunobiology and Opportunity

“…Utilising this model, granulomas, macrophage and eosinophil rich structures enclosing the eggs, were found in the lungs 10-25 weeks after 50 cercariae S. mansoni infection (127). However, these granulomas remained similar in size and cellular constituents over the 10-25 week timescale (127). Immunological modulation (especially decreased granuloma size) is a characteristic feature of liver granulomas (128), and its absence in the surgical ligation model may therefore be a fundamental limitation.…”

“…Early studies used surgical ligation of the portal vein to create a shunt from the portal system to the lungs, in order to increase egg translocation to the lungs (126). Utilising this model, granulomas, macrophage and eosinophil rich structures enclosing the eggs, were found in the lungs 10-25 weeks after 50 cercariae S. mansoni infection (127). However, these granulomas remained similar in size and cellular constituents over the 10-25 week timescale (127).…”