A reason for why infants are less able to fend off viral infections is explained in a mouse study published online this week in Nature Immunology.
Natural killer (NK) cells are a class of white blood cells that help combat viral infections. These cells are especially important early in infection to limit viral replication.
Yasmina Laouar and colleagues find that young mice, like human infants, are more susceptible to viruses because they lack mature NK cells. Exploring why this might be, the authors find that a molecule called TGF-beta limits the proliferation of immature NK precursors and blocks their maturation to fully armed effector cells. Neonatal and infant mice whose blood cells cannot respond to TGF-beta are able to generate functional NK cells and are able to fend off viral infections. Although TGF-beta is typically thought to protect individuals by preventing deleterious inflammation, in young mice it prevents robust immune responses that would protect them from viral challenge. Further investigation is needed to see if this is also true in humans.