The Surprising Strength of Babies' Immune Cells

An immature immune system

For a long time, it has been thought that a baby’s immune system is far weaker than that of an adult due to limited pathogen exposure. However, a recent paper, published in Science Immunology, has questioned these beliefs.

Previous studies found adult T cells outperformed newborn T cells at tasks involved in adaptive immunity – a type of immunity that comes into play when a person's innate immune system is unable to kill an infection. Newborn T cells were less effective at recognizing antigens, forming immunological memory and responding to repeat infections. This led scientists to work under the assumption that an infant's immune system is still immature.

During the COVID-19 pandemic, however, infants were affected to a lesser degree than adults, with many displaying an apparent lack of illness. This observation prompted researchers from Cornell University, including co-corresponding authors Dr. Brian Rudd, an associate professor of microbiology and immunology and Dr. Andrew Grimson, a professor of molecular biology and genetics, to further investigate exactly how the infant immune system works in mice.

Neonatal T cells are not impaired

Rudd and Grimson used a multiomics approach to study how neonatal immune cells respond to an infection compared to those from an adult. They performed immunoassays on T cells from neonatal and adult mice and compared their gene expression profiles using RNA-Seq.

The researchers found the infants’ immune systems worked differently from the adults, but are not impaired.

The neonatal immune cells work alongside the innate immune system, the rapid non-specific part of immunity that does not require antigen recognition. The newborn T cells were activated by proteins that are associated with innate immunity, including transcription factors Bach2 and AP-1, which promote chromatin remodeling, supporting the infants’ immune system.

“One of the most unexpected findings from our study is that neonatal CD8⁺ T cells are more responsive to inflammation than adults because of their ability to undergo chromatin remodeling,” the authors wrote.

The enhanced ability of neonatal T cells allows their immune systems to react quickly in the early stages of infection against a wide array of pathogens.

“These differences likely reflect the type of functions that are most useful to the host at distinct stages of life,” Rudd said.

Babies’ immune systems are just different

Although their results highlighted that neonatal T cells were more efficient at protecting the host during the initial stages of infection, infants' immune systems are less equipped to fight repeat infections with the same pathogen compared to adults.

“It is not possible to say adult T cells are better than neonatal T cells or neonatal T cells are better than adult T cells. They just have different functions,” said Rudd.

The researchers also plan to further investigate how these neonatal T cells persist into adulthood.

“We are also interested in studying how changes in the relative numbers of neonatal T cells in adults contributes to variation in the susceptibility to infection and outcomes to disease,” said Rudd.

Reference: Watson NB, Patel RK, Kean C, et al. The gene regulatory basis of bystander activation in CD8 ⁺ T cells. Sci Immunol. 2024;9(92):eadf8776. doi: 10.1126/sciimmunol.adf8776

This article is a rework of a press release issued by Cornell University. Material has been edited for length and content.