Schistosomiasis remains a major public health problem and it is an
immune disease. The schistosome egg is the primary parasite factor responsible for the overt disease. The eggs release the soluble
antigen, which induces intensive tissue reaction, a granulomatous reaction to the eggs. If
granuloma formation could be suppressed, overt disease might not develop.
Praziquantel is an effective antischistosomal
drug especially for adult worms. However, whether
praziquantel has a suppressing effect on
granuloma formation around schistosome eggs directly remains unclear. The purpose of the present study was to investigate the effect of
praziquantel, especially administered persistently, on
granuloma formation around Schistosoma japonicum eggs in the lung of sensitized mice. Thirty-six mice were divided into three groups averagely. Group A was a control group. First, the mice were injected with schistosomal eggs hypodermically in abdomen, and 10 days later injected with schistosomal eggs intravenously via a tail vein. Group B was a
praziquantel short administration group. In addition to the
injections of schistosomal eggs as the same of Group A, the mice were administered with
praziquantel in a daily dose of 300 mg/kg for 3 days, from 1 day before the
intravenous injection of the eggs. Group C was a
praziquantel prolonged administration group. In addition to the
injections of schistosomal eggs as the same of Group A, the mice were administered with
praziquantel in a daily dose of 150 mg/kg for 5 days weekly until the mice were sacrificed. Three mice of each group were sacrificed on days 7, 14, 28, and 56, respectively after the
intravenous injection of the eggs, and the lung tissues were fixed with
formalin and the slices were HE stained. The
granulomas containing eggs in their centers were selected, and 25-30
granulomas from the animals of each group were measured at each time period. The mean areas of egg
granulomas of each group were calculated, and the neutrophilic granulocytes, eosinocytes, lymphocytes, fibroblasts, and macrophages within the egg
granulomas were counted. The mean numbers of them of each group were calculated. All the data of each group were analyzed and compared statistically. On day 56 after the
intravenous injection of the eggs, the mean area of schistosomal egg
granulomas in group B was (227.4 ± 728.0) × 10(3) μm(2), less than that of [(297.9 ± 153.3) × 10(3) μm(2)] in group A, and the suppression rate was 23.7% (P < 0.05). On days 7, 14, 28, and 56, the mean areas of schistosomal egg
granulomas in group C were (575.8 ± 155.6) × 10(3) μm(2), (310.5 ± 854.0) × 10(3) μm(2), (267.7 ± 513.3) × 10(3) μm(2), and (214.9 ± 446.4) × 10(3) μm(2), respectively, significantly less than those of [(692.7 ± 232.6) × 10(3) μm(2), (439.4 ± 165.0) × 10(3) μm(2), (385.7 ± 129.3) × 10(3) μm(2), and (297.9 ± 153.3) × 10(3) μm(2)] in group A. The suppression rates were 16.9%, 29.3%, 30.6%, and 27.9%, respectively (P values <0.05). On day 56, the mean numbers of neutrophilic granulocytes were 11.4 ± 5.0 in group A and 5.2 ± 3.1 in group C, respectively, with the suppression rate of 54.4% in group C (P < 0.05). On day 56, the mean numbers of eosinocytes within the egg
granulomas were 2.3 ± 2.0, 0.1 ± 0.3, and 0.3 ± 0.6 in groups A, B, and C, respectively, with the suppression rate of 95.7% in group B and 87.0% in group C (P values <0.05). On day 56, the mean numbers of macrophages within egg
granulomas were 14.3 ± 6.9 in group C, compared with 18.6 ± 8.2 in group A, the suppression rate was 23.1% (P < 0.05). On day 56, the mean numbers of fibroblasts within the egg
granulomas were 6.6 ± 4.4 and 5.8 ± 2.6 in groups B and C, respectively, and compared with 14.3 ± 7.8 in group A, the increasing extents decreased by 53.8% and 59.4%, respectively (P values <0.05). Therefore, the administration of
praziquantel, especially the prolonged administration, can suppress the formation of schistosomal egg
granulomas, including reduction in the areas of
granulomas and suppression of the inflammatory cells and the
hyperplasia of fibroblasts within
granulomas.