Efficacy of an antipathology vaccine in murine schistosomiasis administered with and without chemotherapy.

This study was undertaken to study the efficacy of praziquantel (PZQ) in potentially tolerized Schistosoma mansoni infected, egg-injected C57BL/6 mice, receiving multiple administrations of soluble egg antigen (SEA) intravenously (i.v.). Four animal groups were studied. Experimental group I received four injections of SEA (10 micrograms) intravenously on days -7, -5, -3 and -2 before infection and PZQ orally (500 mg/kg over two consecutive days 7 weeks post-infection. Three control groups received the following treatment: group II received the same tolerizing dose of SEA without PZQ, group III received PZQ in the same dose and at the same timing. Group IV received S. mansoni infection and egg injection 8 weeks post-infection and served as an infected, egg-injected control. Egg injection was conducted 8 weeks post-infection using viable S. mansoni eggs via the tail vein. Animals were killed 16 days post-egg injection, i.e. 10 weeks post-infection. After sacrifice, lungs and livers were removed for histopathological study and measurement of granuloma diameters. Spleens and serum were collected for the assay of lymphoproliferative response to SEA and antischistosomal immunoglobulins. The worm and egg burdens were also studied. Compared to infected, egg-injected untreated controls, repeated i.v. administrations of SEA down-regulated egg-injected (pulmonary) and egg-deposited (hepatic) granulomas and the lymphoproliferative response to SEA. Antischistosomal IgG level was increased. Susceptibility to S. mansoni infection was not found to be different from that in the infected, egg-injected controls. PZQ in the dose used caused complete eradication of worms, disappearance of immature egg stages, decrease in the number of mature eggs and an increase in the number of dead eggs. Hepatic granuloma diameter, lymphoproliferative response to SEA and IgG level were reduced. In mice receiving a combined regimen of multiple SEA administrations and PZQ with down-regulated granuloma and reduced lymphoproliferative response to SEA, the efficacy of PZQ was the same as in mice receiving PZQ alone. This was shown by comparable grades of worm and egg reduction. The histopathological examination of liver and lung sections in the different treated groups revealed moderate to small-sized hypocellular granulomas. Although no statistically significant difference was recorded between the mean granuloma diameters of the experimental group receiving both the tolerizing dose of SEA and PZQ compared to the group receiving the tolerizing dose of SEA without chemotherapy, this experimental group showed the least associated histopathological parenchymal changes. It appears from this work that combined SEA and PZQ provided many complementary goals; a reduction of egg-induced pathology, minimal parenchymal changes and the eradication of worms.