Oswald Theodore Avery studied strains of pneumococcus of the genus Streptococcus in the US in the first half of the twentieth century. This bacterium causes pneumonia, a common cause of death at the turn of the twentieth century. In a 1944 paper, Avery demonstrated with colleagues Colin Munro MacLeod and Maclyn McCarty that deoxyribonucleic acid, or DNA, instead of protein, formed the material of heritable transformation in bacteria. Avery helped untangle some of the relationships between genes and developmental processes.

In 2016, researcher Thomas Gensollen and colleagues published “How Colonization by Microbiota in Early Life Shapes the Immune System,” hereafter, “Microbiota Shapes the Immune System,” in Science. The article reviews [what is known about?] how microbial colonization impacts immune development in newborns. Because the immune system protects the body from infection, an individual’s microbiome composition also affects susceptibility to certain diseases. Specifically, the authors discuss microbe colonization during early life, a time they refer to as the window of opportunity for future disease susceptibility. That window of opportunity is a period where environmental influences more easily shape the infant’s immune cells and their functions. In turn, the authors present that window as an optimal time for treating disorders associated with the microbiome and the immune system. “Microbiota Shapes the Immune System” reviewed data from dozens of articles to show that there is a narrow window during infancy where microbiome interactions directly or indirectly influence immune development, a potential area for interventional methods to target immune development.

In 2010, Maria Dominguez-Bello, Elizabeth Costello, Monica Contreras, and colleagues published “Delivery Mode Shapes the Acquisition and Structure of the Initial Microbiota Across Multiple Body Habitats in Newborns,” hereafter “Delivery Mode” in the journal Proceedings of the National Academy of Sciences. The term microbiota, which the authors use interchangeably with the term microbiome, refers to the collection of microorganisms, including bacteria, fungi, and viruses, found in and on the human body. The development of the microbiome, which begins at birth when a newborn is first exposed to the mother’s microbiota, impacts the development of the immune system, and how a person’s body responds to disease. Though researchers in the early 2000s were aware of a connection between delivery mode and the neonatal gut microbiome, they knew little about how delivery mode affects a neonate’s microbiome beyond the gut. Dominguez-Bello and associates’ experiment was one of the first to show that a neonate’s microbial community is uniform across their body and elaborate on the differences in microbiomes across delivery methods, which can make neonates born via c-section more susceptible to conditions such as asthma.