Maternal infection with Trypanosoma cruzi and congenital Chagas disease induce a trend to a type 1 polarization of infant immune responses to vaccines

Abstract

Background: We previously showed that newborns congenitally infected with Trypanosoma cruzi (M+B+) display a strong type 1 parasite-specific T cell immune response, whereas uninfected newborns from T. cruzi-infected mothers (M+B-) are prone to produce higher levels of proinflammatory cytokines than control neonates (M-B-). The purpose of the present study was to determine if such fetal/neonatal immunological environments could alter the response to standard vaccines administered in early life.

Methodology: Infants (6-7 months old) living in Bolivia, an area highly endemic for T. cruzi infection, and having received Bacillus Calmette Guerin (BCG), hepatitis B virus (HBV), diphtheria and tetanus vaccines, were enrolled into the M+B+, M+B-, M-B- groups mentioned above. The production of IFN-gamma and IL-13, as markers of Th1 and Th2 responses respectively, by peripherical blood mononuclear cells stimulated with tuberculin purified protein derivative of Mycobacterium tuberculosis (PPD) or the vaccinal antigens HBs, diphtheria toxoid (DT) or tetanus toxoid (TT), as well as circulating levels of IgG antibodies against HBsAg, DT and TT were analyzed in infants. Cellular responses to the superantigen SEB were also monitored in M+B+, M+B-, M-B-infants and newborns.

Principal findings: M+B+ infants developed a stronger IFN-gamma response to hepatitis B, diphtheria and tetanus vaccines than did M+B- and M-B- groups. They also displayed an enhanced antibody production to HBsAg. This was associated with a type 1-biased immune environment at birth, since cells of M+B+ newborns produced higher IFN-gamma levels in response to SEB. M+B- infants produced more IFN-gamma in response to PPD than the other groups. IL-13 production remained low and similar in all the three groups, whatever the subject's ages or vaccine status.

Conclusion: These results show that: i) both maternal infection with T. cruzi and congenital Chagas disease do not interfere with responses to BCG, hepatitis B, diphtheria and tetanus vaccines in the neonatal period, and ii) the overcoming of immunological immaturity by T. cruzi infection in early life is not limited to the development of parasite-specific immune responses, but also tends to favour type 1 immune responses to vaccinal antigens.

Figure 1. IFN-γ and IL-13 productions in response to SEB by blood mononuclear cells from newborns and infants.

Newborns and 6 to 7 months-old infants were born either to T. cruzi-infected (M+) or not infected mothers (M−), and either congenitally infected (B+) or not (B−). Cells were cultured during 6 days in the presence of 10 ng/mL SEB (staphylococcal enterotoxin B). Results of cytokines levels measured by ELISA (individual results and geometric means) are shown. * : p<0.05 and ** : p<0.005 (Mann-Withney U test).

Figure 2. Antibody levels against hepatitis B, diphtheria and tetanus vaccines in newborns and infants.

Plasma levels of specific IgG in newborns and 6 to 7 months old infants born to mothers infected (M+) or not (M−) with T. cruzi, and congenitally infected (B+) or not (B−), and vaccinated at 2, 4 and 6 months against hepatitis B, diphtheria and tetanus. Results are shown as geometric means; extreme values are indicated, as well as the proportion of samples showing an antibody level above the indicated threshold of protection. * : p<0.05 (Mann Withney U test).

Figure 3. Levels of antibody IgG sub-classes against hepatitis B in vaccinated infants.

Plasma levels of HbsAg-specific IgG sub-classes in 6 to 7 months old infants born to mothers infected (M+) or not (M−) with T. cruzi, and congenitally infected (B+) or not (B−), and vaccinated at 2, 4 and 6 months against hepatitis B. Results are displayed as box and whiskers (n = 6 M−B−, 13 M+B− and 9 M+B+). * : p<0.05 compared with infants from other groups (Man Withney U test).

Figure 4. Cytokine response to PPD in infants vaccinated with BCG.

IFN-γ and IL-13 production in response to tuberculin purified protein derivative of M. tuberculosis (PPD) by PBMC from 6 to 7 months old infants born to mothers infected (M+) or not (M−) with T. cruzi, and congenitally infected (B+) or not (B−), and having received at birth the BCG vaccine. PBMC were cultured during 6 days in the presence of 10 µg/mL PPD. Results of cytokines levels measured by ELISA are shown (individual results and geometric means). The proportions of responders (i.e. showing detectable levels of cytokines) are also shown. * : p<0.05 and ** : p = 0.006 compared with M−B− infants (Mann-Withney U test for means and Fisher test for proportions).