A team led by researchers at Columbia University, in the United States, has identified a tissue containing specialised immune cells present only in infants. The tissue helps them mount an immune response against respiratory pathogens (such as SARS-Cov-2 and common colds) even though they may have never been exposed to them before.
The study, which was published in Nature Immunology, uncovered what has been named BALT or bronchus-associated lymphoid tissue in the lungs of young children. The tissue was seen to contain specialised immune cells (B cells, CD4+ T cells) and active germinal centres.
Germinal centres are unique spots in the body’s defence centres, similar to lymph nodes, where B cells improve antibody production and switch antibody types.
“We know little about how the immune system develops throughout life, and most of what we know about immune system development in children comes from animal studies,” says Dr Donna Farber, an expert in immune system development at Columbia University, in a statement.
The researchers wrote that BALT begins developing when babies are 6-12 months and is mostly found around lung airways. But as the body’s immune system develops and memory T cells take over in fighting pathogens, it disappears by the time the child is 3 years old.
By analysing lung tissue samples from deceased paediatric organ donors, the research team found that B cells were more active in adjusting their antibodies compared to B cells in lymph nodes. This heightened activity enhances the immune system’s ability to fight infections.
However, B cells are not produced in the lungs; therefore this suggests a unique immune activity in the lung environment during early childhood.
“BALT enables the lung to make antibodies to respiratory pathogens well before T cell memory has developed but falls apart in later childhood when they are no longer needed,” adds Faber.
This study provides compelling evidence that BALT acts as an early-life adaptation, mobilising localised immune protection against various respiratory pathogens during this critical developmental stage.
The findings could have profound implications for understanding how infants and young children respond to respiratory infections, hopefully leading to strategies for enhancing immune protection in paediatric populations.