Newborns’ immune system not undeveloped version of adults’ immune system, research finds

Scientists have long believed that a newborn’s immune system was an immature version of an adult’s, but new research shows that newborns’ T cells—white blood cells that protect from disease—outperform those of adults at fighting off numerous infections, Cornell University reported.

These results help clarify why adults and infants respond differently to infections and pave the way for controlling T cells’ behavior for therapeutic applications.

This discovery was described in a paper, “The Gene Regulatory Basis of Bystander Activation in CD8+ T cells,” which published February 23 in the journal Science Immunology. Brian Rudd, associate professor in the Department of Microbiology and Immunology in the College of Veterinary Medicine, and Andrew Grimson, professor in the Department of Molecular Biology and Genetics in the College of Agriculture and Life Sciences, co-led the study.

“The immune system is almost always viewed from an adult perspective,” Rudd said. For example, adult T cells outperform newborn T cells at tasks including recognizing antigens, forming immunological memory and responding to repeat infections, which has led to the belief that infants’ T cells were just a weaker version of the adult ones. But during the COVID-19 pandemic, many were surprised by the apparent lack of illness in infants, bringing this long-standing belief into question.

Interested in understanding these age-related differences, Rudd and Grimson discovered that newborn T cells are not deficient. Instead, they are involved in a part of the immune system that does not require antigen recognition, the innate arm of the immune system. While adults T cells use adaptive immunity—recognizing specific germs to then fight them later ¬– newborn T cells are activated by proteins associated with innate immunity, the part of the immune system that offers rapid but nonspecific protection against microbes the body has never encountered.

“Our paper demonstrates that neonatal T cells are not impaired, they are just different than adult T cells and these differences likely reflect the type of functions that are most useful to the host at distinct stages of life,” Rudd said.

Neonatal T cells can participate in the innate arm of the immune system. This enables newborn’s T cells to do something that most adult T cells cannot—respond during the very first stages of an infection and defend against a wide variety of unknown bacteria, parasites, and viruses.

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