Background and objectives The human immune system has evolved to balance protection against infection with control of immune-mediated damage and tolerance of commensal microbes. Such tradeoffs between protection and harm almost certainly extend to the immune system of milk. Methodology Among breastfeeding mother-infant dyads in Kilimanjaro, Tanzania, we characterized in vitro proinflammatory milk immune responses to Salmonella enterica (an infectious agent) and Escherichia coli (a benign target) as the increase in interleukin-6 after 24 hours of incubation with each bacterium. We characterized incident infectious diseases among infants through passive monitoring. We used Cox proportional hazards models to describe associations between milk immune activity and infant infectious disease. Results Among infants, risk for respiratory infections declined with increasing milk in vitro proinflammatory response to S. enterica (HR: 0.68; 95% CI: 0.54, 0.86; p: 0.001), while risk for gastrointestinal infections increased with increasing milk in vitro proinflammatory response to E. coli (HR: 1.44; 95% CI: 1.05, 1.99; p: 0.022). Milk proinflammatory responses to S. enterica and E. coli were positively correlated (Spearman’s rho: 0.60; p: 0.000). Conclusions and implications These findings demonstrate a tradeoff in milk immune activity: the benefits of appropriate proinflammatory activity come at the hazard of misdirected proinflammatory activity. This tradeoff is likely to affect infant health in complex ways, depending on prevailing infectious disease conditions. How mother-infant dyads optimize proinflammatory milk immune activity should be a central question in future ecological-evolutionary studies of the immune system of milk. Lay Summary While vital to infant health, the immune system of milk (ISOM), like all immune activity, comes with potential for both protection and harm. We described the ISOM’s capacity to respond to bacteria among mother-infant pairs, and found that milk immune activity may both lower and increase infants’ infectious disease risk.

Introduction Globally, approximately 15 million babies are born before term each year. Of these, more than 1 million die within the first 28 days of their life. Understanding the mortality rate and its predictors during neonatal period among preterm babies is crucial to help designing interventions to avert the situation. This study aimed to determine the neonatal mortality rate and associated factors among preterm babies born in Moshi Municipality, Tanzania. Methodology A prospective cohort study was conducted in three hospitals in Moshi Municipality from December 2016 to May 2017. All live births at gestational age of <37 weeks and those of <24 hours were studied. Babies who died prior to gestation age assessment and those whose mother did not consent were excluded. Cox regression model was used to estimate maternal and fetal factors associated with neonatal mortality. A p-value of <0.05 was considered statistically significant. Results A total of 311 of preterm babies were recruited from 265 mothers and were followed for 28 days. The neonatal mortality rate was 6.5deaths per 1,000 preterm live births (95% CI: 4.83-8.61). It was higher among extremely preterm babies compared to very preterm ones (HR: 38.24; 95% CI: 16.62-87.96) versus (HR: 8.01; 95% CI: 3.96-16.20) respectively. Apgar score of <7 at 1st minute (HR: 14.03; 95% CI: 7.27-27.06), respiratory distress syndrome (HR: 8.14; 95% CI: 4.27-15.54) and antepartum hemorrhage (HR: 3.32; 95% CI: 1.49-7.39) were significantly associated with neonatal mortality. Conclusion Preterm birth complication is the major cause of neonatal death in the study setting. Interventions to address the identified risk factors may reduce neonatal mortality among preterm babies.

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