Are the cellular immune responses of children and adults with Schistosoma mansoni infection intrinsically different? Cytokines produced ex vivo in response to antigens and mitogens

In recently exposed communities, intensity of schistosomiasis infection increases as children age and then drops again in adulthood, indicating that host maturity is an important aspect of resistance to schistosomiasis. We investigated whether the cellular immune response to the parasite was correlated with age in subjects with similar daily patterns of exposure, current intensities of infection and number of years of exposure.

The cellular immune response of subjects with either ‘low’ (under 200 eggs per gram (EPG)) or ‘high’ (over 400 EPG) intensities of infection was investigated, in a recently established focus where subjects had similar histories of exposure and number of years of experience with Schistosoma mansoni. Subject's whole blood was cultured with adult worm antigen (AWA), a mixture of phytohaemagglutinin (PHA) and lipopolysaccharide (LPS), or left unstimulated, and culture supernatants were tested for IL-4, IL-5, IL-10 and IFN-γ.

Children and adults tended to respond differently to schistosome antigen. The most statistically significant illustration of this was the negative correlation between age and IL-5 produced by samples from people with low intensities of infection cultured with AWA (P < 0·003, P < 0·05 after Bonferroni correction). IL-10 produced by samples cultured with PHA and LPS was also notably lower in children than in adults, although not formally significant after Bonferoni correction.

This indicates that it is possible for age, independently of intensity of infection or experience with the parasite, to influence the immune response to schistosomiasis.