Introduction: The present study is an attempt to evaluate the protective effect of schistosomula antigen and the current antischistosomal drug praziquantel (PZQ) as a reference drug on mice infected with S. mansoni.
Material and Methods: Mice were vaccinated by irradiated or non-irradiated schistosomula antigen, both at a dose of 100 ug protein/mice once weekly for 3 weeks, before infection with alive cercariae and compared with the treatment with i.m. injection of praziquantel at a dose of 40 mg/kg b.wt. 4 times once weekly for 4 weeks after infection. The degree of resistance or protection induced by immunization and chemotherapy was assessed 45 days post–infection and evaluated by physiological, parasitological, immunological as well as histological parameters.
Results: The results indicated that immunization with γ-irradiated antigen at 20 Krad or the treatment with PZQ resulted in significant reduction in ova count in liver and intestine tissues more than those vaccinated with non-irradiated antigen compared with infected group. Immunized group with irradiated antigen and the group treated with PZQ showed a significant decrease in liver enzymes activity (ALT, AST and γ-GT), while in immunized group with non- irradiated antigen, there was a significant increase in AST and γ-GT as compared to infected group. The level of alkaline phosphatase enzyme was significantly increased in all investigated groups compared to infected one. Treatment with PZQ or immunization with irradiated or non- irradiated schistosomula antigen induced amelioration in serum IL-10 and TNF-α. Scanning electron microscope demonstrated normal mature worms in infected group after 45 days from infection. In contrast, many changes were detected in the rest groups as alterations in the tegument, implosion of tubercles which appeared pealed and sloughed off and most of the spines were detached and separated.
Histological examination of liver sections of infected mice revealed lobular cellular infiltration and cloudy swelling in hepatocytes with occurrence of necrotic foci. Also, granuloma of infiltrating cells was noticed around the portal structures and inbetween the degenerated cells. Congested portal vein could be seen lodged with adult worms and the portal tracts showed fibrous thickening. Whereas, the lung revealed destructed bronchioles which appeared surrounded by intense inflammatory foci. Thickened interalveolar septae were also marked, however many alveoli appeared with shed destroyed epithelium. Moreover, peribronchiolar and perivascular fibrosis was quite prominent. Gross pathological alterations were observed in both liver and lung of immunized groups with non-irradiated antigen. In controversy, immunization with irradiated antigen can reduce the granulomatous reaction and collagen deposition. There are also little inflammation and less congestion, however the hepatic and pulmonary architectures appeared otherwise normal. The present histological findings proved that PZQ has a valuable schistosomicidal effect but some pathological changes are still detectable.
Conclusion:On the whole, it could be concluded that irradiated antigen produced marked protection against S.mansoni infection and this may reflect its possible beneficial effect on the diseased liver and lung.