Both very low- and very high in vitro cytokine responses were associated with infant death in low-birth-weight children from Guinea Bissau

Abstract

Background: The mechanisms behind heterologous immunity and non-specific effects of vaccines on mortality are not well understood. We examined associations between cytokine responses and subsequent mortality in low-birth-weight infants in Guinea-Bissau.

Methods: A low-birth-weight trial randomized children to Bacille Calmette-Guérin (BCG) at birth or later according to local policy. Blood samples were obtained from a sub-group at age 6 weeks. Interleukin (IL)-5, IL-10, IL-13, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α were measured in whole-blood cell cultures stimulated with lipopolysaccharide (LPS), phytohaemagglutinin (PHA), or purified protein derivative (PPD). The outcome was mortality between bleeding and 1 year of age. Non-linear associations between cytokine responses and mortality were examined.

Results: Cytokine measurements were available from 390 children. The mortality rate (MR) was high (6.8/100 person-years-observation (PYO)). Both low and high cytokine responses to LPS and PHA were associated with high mortality (MR up to 25/100 PYO in the lowest 10% and 9.2/100 PYO in the highest 10%). In BCG-vaccinated children, higher IFN-γ responses to PPD were associated with better survival (MR ratio = 0.43 (0.24-0.77)).

Conclusions: Data presented a rare opportunity to explore associations between cytokine responses and mortality. Both low and high cytokine responses were associated with high mortality; a balanced response to invading pathogens seems preferable.

Figure 1. Information on children who died: diagnosis, date of death, time from bleeding to death in days, sex, randomization to +/− BCG, vaccination with BCG, DTP and measles (MV), and cytokine log-z-score percentiles.

Note: RI: Respiratory infection; Heart: Heart condition; TB: tuberculosis. The percentile indicates which 10% percentile the corresponding log-z-score belongs to. Vaccine information may be incomplete since the vaccination card was often not seen after death and children could have been vaccinated between the last home visit and the time of death.

Figure 2. Flexible shapes of the associations between the cytokine log-z-scores and the mortality rate

. Notes: The curves show mortality rate ratios comparing the mortality rate of children with a given log-z-score and age to the mortality rate of children aged 38 days at bleeding with a log-z-score equal to zero (Methods S1). For PPD the association is only shown in the group randomized to BCG at birth (+BCG) as there was little cytokine production induced by PPD in the group randomized to BCG later (−BCG).

Figure 3. Histograms of the log₂-concentrations of TNF-α and IL-10 in response to stimulation with LPS.

Notes: The distribution of TNF-α showed a tail of low concentrations and 6 outlying observations. The distribution of IL-10 included a mixture of responders with normally distributed measurements and non-responders (12%) with no or a very weak response to LPS.