Elevated IgG Responses in Infants Are Associated With Reduced Prevalence of Infection.

Background: It is unclear whether antibodies can prevent () infection. In this study, we examined the relationship between total plasma IgG levels, IgG elicited by childhood vaccines and soil-transmitted helminths, and infection prevalence, defined by positive QuantiFERON (QFT) test.

Methods: We studied 100 uninfected infants, aged 4-6 months. Ten infants (10%) converted to positive QFT test (QFT+) within 2 years of follow-up for infection. Antibody responses in plasma samples acquired at baseline and tuberculosis investigation were analyzed by enzyme-linked immunosorbent assay and ImmunoCAP assay.

Results: QFT- infants displayed a significant increase in total IgG titers when re-tested, compared to IgG titers at baseline, which was not observed in QFT+ infants. Bacille Calmette-Guérin (BCG) vaccine-specific IgG2 and live-attenuated measles vaccine-specific IgG were raised in QFT- infants, and infants who acquired an infection did not appear to launch a BCG-specific IgG2 response. IgG titers against the endemic helminth increased from baseline to QFT re-testing in all infants.

Conclusion: These data show raised IgG associates with a QFT-status. Importantly, this effect was also associated with a trend showing raised IgG titers to BCG and measles vaccine. Our data suggest a possible protective association between raised antibody titers and acquisition of infection, potentially mediated by exposure to antigens both related and unrelated to .