Filarial infection during pregnancy has profound consequences on immune response and disease outcome in children: A birth cohort study

Abstract

Background: Current Global Program to Eliminate Lymphatic Filariasis (GPELF) that prohibits pregnant mothers and children below two years of age from coverage targeted interruption of transmission after 5-6 rounds of annual mass drug administration (MDA). However, after more than 10 rounds of MDA in India the target has not been achieved, which poses challenge to the researchers and policy makers. Several studies have shown that in utero exposure to maternal filarial infections plays certain role in determining the susceptibility and disease outcome in children. But the mechanism of which has not been studied extensively. Therefore the present study was undertaken to understand the mechanism of immune modulation in children born to filarial infected mother in a MDA ongoing area.

Methodology and principal finding: To our knowledge this is the first study to conduct both cellular and humoral immunological assays and follow up the children until older age in a W bancrofti endemic area,where the microfilariae (Mf) rate has come down to <1% after 10 rounds of MDA. A total 57 (32: born to infected, 25: born to uninfected mother) children were followed up. The infection status of children was measured by presence of Mf and circulating filarial antigen (CFA) assay. Filaria specific IgG1, IgG2, IgG3 and IgG4 responses were measured by ELISA. Plasma level of IL-10 and IFN-γ were evaluated by using commercially available ELISA kit. The study reveals a high rate of acquisition of filarial infection among the children born to infected mother compared to uninfected mothers. A significantly high level of IgG1 and IgG4 was observed in children born to infected mother, whereas high level of IgG3 was marked in children born to uninfected mother. Significantly high level of IL-10 positively correlated with IgG4 have been observed in infected children born to infected mother, while high level of IFN-γ positively correlated with IgG3 was found in infection free children born to mother free from infection at the time of pregnancy. Moreover a negative correlation between IL-10 and IFN-γ has been observed only among the infected children born to infected mother.

Significance conclusion: The study shows a causal association between maternal filarial infection and impaired or altered immune response in children more susceptible to filarial infection during early childhood. As lymphatic damage that commences in childhood during asymptomatic stage has major implications from public health point of view, understanding maternal programming of the newborn immune system could provide a basis for interventions promoting child health by implementing MDA campaigns towards all women of childbearing age and young children in achieving the target of global elimination of LF.

Fig 1. The flow diagram of the cohort study.

Fig 2. Filaria-specific IgG isotype antibody responses in children during follow-up.

Antibody units of filaria-specific IgG1 (A), IgG2 (B), IgG3(C) and IgG4 (D) response in children born from filarial infected and uninfected mothers during follow-up study. Each dot represents an individual's antibody levels and lines represent the mean values. Ch+ve: children were CFA positive; Ch−ve: children CFA negative.

Fig 3. The relationship between IgG antibody isotypes with circulating filarial antigen (CFA) in infected children (n = 14) born to infected mother during the follow-up study.

Each dot represents value from a single subject while the solid lines represent the regression lines. Values of P and r derive from Spearman’s correlation analysis. (A) IgG1 vs CFA (r = -0.29, p = 0.30) (B) IgG2 vs CFA (r = -0.008, p = 0.97) (C) IgG3 vs CFA (r = - 0.115, p = 0.69) (D) IgG4 vs CFA (r = 0.53, p = 0.04).

Fig 4. Plasma level of IL-10 and their correlation with IgG4 in CFA +ve and CFA-ve children born from infected and uninfected mother at the time of follow-up.

(A) Each dot represents an individual's IL-10 level and lines represent the mean values. Ch+ve: children were CFA positive; Ch−ve: children CFA negative. Correlation between IL-10 and IgG4 in CFA +ve children (n = 14, B) and CFA–ve children (n = 18, C) born to infected mother. Each dot represents value from a single subject while the solid lines represent the regression lines. Values of p and r derive from Spearman’s correlation analysis.

Fig 5. Plasma level of IFN-v and their correlation with filarial specific IgG3 in CFA +ve and CFA-ve children born from infected and uninfected mother at the time of follow-up.

(A) Each dot represents an individual's IFN-γ level and lines represent the mean values. Ch+ve: children were CFA positive; Ch−ve: children CFA negative. (B) Correlation between IFN-γ and IgG3 in CFA–ve children (n = 24) born to infection free mother. Each dot represents value from a single subject while the solid lines represent the regression lines. Values of p and r derive from Spearman’s correlation analysis.

Fig 6. The relationship between regulatory cytokine IL-10 with IFN-γ level of CFA +ve and CFA–ve children born to infected and uninfected mother during the follow-up study.

Each dot represents value from a single subject while the solid lines represent the regression lines. Values of P and r derive from Spearman’s correlation analysis. (A) CFA+ve children from infected mother (n = 14, r = -0.79, p = 0.007) (B) CFA–ve children from infected mother (n = 18, r = -0.16, p = 0.51) (C) CFA negative children of uninfected mother (n = 24, r = 0.07, p = 0.73).