During recruitment period for the nested cohort, 2208 women were recruited to the main study of whom 387 had stool samples positive for Schistosoma mansoni. Cytokine response data at enrolment was available on 103 women who received praziquantel and 105 women who received placebo for praziquantel. For logistical reasons (missed appointments, omission of schistosome antigens in assays or insufficient samples) numbers analysed for particular time points varied: results available for the praziquantel and placebo groups, respectively, were 80 and 72 at six weeks post-enrolment (while still pregnant), 91 and 95 six weeks after delivery and 68 and 77 six weeks after post-delivery treatment. At baseline, the praziquantel and placebo groups showed similar characteristics of the women, intensity of schistosome infection, prevalence of hookworm and HIV, and profile of cytokine responses to schistosome antigens (). At baseline, type 2 cytokine responses to SWA showed positive associations with schistosome infection intensity (IL-4 (rho=0.13 p=0.061), IL-5 (rho=0.14 p=0.036), IL-13 (rho=0.16 p=0.021)). Baseline responses to SEA showed negative associations with infection intensity for IFNγ (rho −0.17 p=0.017),and IL-13 (−0.14 p=0.041), and a positive association for IL-4 (rho=0.14 p=0.05). Cytokine responses to SWA and SEA showed no association with maternal age, estimated gestational age or with other co-infections such as hookworm.
Comparison of characteristics at enrolment before treatment between the praziquantel and placebo groups
Cytokine responses to SWA and SEA are suppressed during pregnancy
Results from the placebo group were examined in order to assess effects of pregnancy on anti-schistosome cytokine responses in the absence of treatment (figures and ). At six weeks post-enrolment, IFNγ, IL-5 and IL-13 responses to SWA and SEA were lower than at enrolment (p=0.008 for IFNγ and IL-5 and p=0.006 for IL-13 to SWA; p<0.001 for IFNγ, p=0.002 for IL-5 and p=0.001 for IL-13 to SEA). At six weeks after delivery IFNγ, IL-5 and IL-13 responses to SWA had increased and were higher than at enrolment (p=0.02 for IFNγ, p=0.007 for IL-5 and p<0.001 for IL-13) and at six weeks post-enrolment (p<0.001 for IFNγ, p=0.003 for IL-5 and p=0.001 for IL-13); similarly, IFNγ and IL-13 responses to SEA were significantly higher than at six weeks post-enrolment (p=0.009 for IFNγ and p=0.002 for IL-13). IL-2, IL-4 and IL-10 responses showed no statistically significant changes.
Whole blood culture cytokine levels in response to SWA and effect of praziquantel treatment during pregnancy or after delivery
Whole blood culture cytokine levels in response to SEA and effect of praziquantel treatment during pregnancy or after delivery
Thus IFNγ, IL-5 and IL-13 responses to SWA and SEA were suppressed during pregnancy: they declined with progressing pregnancy and were higher, after delivery, than at either time-point during pregnancy.
Praziquantel treatment during pregnancy causes significant boost in cytokine responses to SWA and SEA
Results during pregnancy were examined in the praziquantel group, and compared with results in the placebo group, in order to assess the effect of praziquantel treatment during pregnancy. Among the women who received praziquantel at enrolment (), cytokine production in response to SWA at six weeks post-enrolment was significantly higher than at enrolment (p=0.01 for IFNγ and IL-2; p<0.001 for IL-4, IL-5, IL-13 and IL-10). At six weeks post-enrolment cytokine responses to SWA were significantly higher among the women in the praziquantel group than among the placebo group (p<0.001 for IFNγ, IL-5, IL-13 and IL-10; p=0.003 for IL-2 and IL-4).
The effects of praziquantel treatment during pregnancy on responses to SEA were more limited (). Among women who received praziquantel at enrolment, production of IL-2, IL-5 and IL-13 in response to SEA had increased at six weeks post-enrolment (p=0.02 for IL-2, p=0.01 for IL-5 and 0.002 for IL-13). At six weeks post-enrolment, responses to SEA were significantly higher among the women in the praziquantel group than among the placebo group for IL-5 (p=0.003) and IL-13 (p<0.001).
Pregnancy is associated with reduced boost in cytokine responses to SWA and SEA
The magnitude of the praziquantel-induced boost in cytokine responses (between treatment and six weeks after treatment) was compared between the praziquantel group (first-treated at enrolment during pregnancy) and the placebo group (first-treated six weeks after delivery), in order to assess the influence of pregnancy on the boost in responses.
Initial comparisons showed that the boost was lower for treatment during pregnancy than for treatment after delivery for all responses except for IL-5 and IL-13 to SWA (). Several possible sources of bias were considered in relation to this analysis because, at the time of treatment, the group first-treated after delivery (originally the placebo group) differed in several important ways from the group first-treated during pregnancy (originally the praziquantel group). The pre-treatment prevalence of hookworm was lower in the group first-treated after delivery (since 47% had already received albendazole, ); and 100% of the group first-treated after delivery received albendazole concurrently with their first praziquantel treatment, compared to 55% of those first-treated during pregnancy. However, analyses during pregnancy showed no effect of hookworm co-infection or of concurrent albendazole on the boost in ant-schistosome responses following praziquantel treatment (data not shown), so these differences were considered unlikely to bias the comparison. Pre-treatment levels of cytokine response were higher in the group first-treated after delivery. Although no major difference in enrolment schistosome infection intensity was noted between the two groups, enrolment schistosome intensity showed positive correlations with post-treatment SWA-specific IL-4 (rho=0.38 p<0.001), IL-5 (rho=0.21 p=0.05), and IL-13 (rho=0.23 p=0.039) responses. Post-treatment responses to SEA showed a tendency to negative correlations with enrolment schistosome intensity which did not attain statistically significant levels. However, after adjustment for pre-treatment cytokine responses and enrolment infection intensity the boost in responses remained markedly higher for women treated after delivery than those treated during pregnancy for all responses except IL-5, IL-13 to SWA and IL-2 to SEA ().
Comparison of the change in cytokine responses to SWA and SEA at six weeks following praziquantel treatment during pregnancy or after delivery; adjusted for pre-treatment cytokine responses and S. mansoni infection intensity
In keeping with the suppression of responses during pregnancy and the reduced boost in response following treatment during pregnancy, all six-week-post-treatment responses were lower following treatment during pregnancy than following treatment after delivery. However, among women first-treated during pregnancy, the responses had increased at six weeks after delivery and were not significantly different from the responses at six weeks post-treatment among those first-treated after delivery; except IL-4 and IL-10 to SWA which were still lower among women first-treated during pregnancy than among women first-treated after delivery (p=0.002 for IL4 and 0.008 for IL-10).
Pregnancy is not associated with reduced cure rate
To address the hypothesis that suppression of the boost in immune response during pregnancy is associated with reduced cure rate, infection intensity at six weeks after treatment was compared between the group first-treated during pregnancy and the group first-treated after delivery. Of the 80 women in the group first-treated during pregnancy accessed for cytokine responses at six weeks following treatment, 68 (85.0%) did not have egg detected in their stool, eight (10.0%) had light infection, three (3.8%) had moderate infection and one (1.2%) still had heavy infection. Of the 77 women in the group first-treated after delivery, eggs were not detected in 68/76 (89.5%) of the women and 8/76 (10.5%) still had light infection. One of the women did not submit a stool sample at six weeks after the treatment. The difference in post-treatment infection intensity was not statistically significant (p=0.27).