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.