The Role of Schistosoma mansoni Eggs in Immune Protection against Plasmodium berghei Infected Mice

Abstract

The co-occurrence of malaria and schistosomiasis is common in tropical regions of the world. Malaria induces a strong Th1 response while schistosomiasis skews the response to a Th2. Several studies demonstrate a non consistent effect of schistosomiasis infection on progression of malaria. On one hand, schistosomiasis infections protect against cerebral malaria while on the other hand, they are associated with increased malaria severity. This study examined the role of Schistosoma mansoni eggs on Plasmodium berghei malaria progression in BALB/c mice. The objectives were to determine the changes in Th1, Th2 cytokines and IgG levels which are markers associated with malaria and schistosomiasis protection and also determine if S. mansoni eggs lead to protection from P. berghei malaria. Two groups of mice were used: the experimental group and the control group. The experimental group was injected with a triple dose of S. mansoni eggs at ten day interval before being challenged with P. berghei. The control group was infected with P. berghei only. Five mice from both groups were euthanized at each time point (day 3, 6, 9 and 12 post challenge with P. berghei) and the spleen and serum collected. Five mice from each group were monitored throughout the experiment. Parasitaemia was monitored daily using Giemsa stained blood smears. The results showed that the experimental mice exhibited lower levels of P. berghei parasitaemia (15.52%) as compared to the controls (23.06%). However the difference was not significant (p>0.05). IgG levels were found to be higher in the experimental mice compared to controls due to stimulation by soluble egg antigen (SEA). The differences in IgG levels between the two study groups was not significant (p>0.05). The levels of IFN- γ and IL-4 were higher in the experimental mice than the control group though the difference was not significant (p=0.213). The levels of IgG and IL-4 in experimental mice could be responsible for the delay in death reported in these mice and enhanced survivorship. In conclusion, S. mansoni eggs did not induce significant differences in cytokine and IgG levels; nevertheless they contributed to delaying death in the experimental mice by two days by enhancing levels of IgG and IL-4. These findings provide a pointer for further research in this field using higher animal model such as the non human primates for a better understanding of the immunomodulatory role of schistosoma eggs on progression of malaria.