Scientists have claimed that foetal immune cells that are present in adults have specialised roles during infection. In fact, the first immune cells made in early life are fast-acting first responders to microbes in adulthood.

According to the authors, these immune cells -- called CD8+ T cells -- originate in separate parts of the body and are hardwired with intrinsically different properties. While currently it is believed that, around the time of birth, the body switches from making and using foetal T cells to adult T cells to defend itself. 
However, the researchers used a unique study design to show that foetal T cells persist into adulthood and have different roles than adult cells in fighting infection.

"This discovery has led to the new idea that we might be able to predict how individuals will respond to infection based on how many foetal cells are present in the adult pool and isolate the fast-acting foetal-derived cells for certain therapeutic interventions, such as infections and cancer immunotherapy," said lead author Brian Rudd from New York's Cornell University. The findings, published in the journal Cell, showed that the newly formed T cells in adults recognise a signature protein on a pathogen when they first encounter it. That signal then activates the T cells and equips them to fight and proliferate up to 15 times, producing up to 10 million cells in a week.

Once the pathogen has been cleared, most of those adult T cells die, but up to 10 per cent survive and are stored in a pool of memory cells, allowing for a rapid recall response if that same pathogen were to strike again.Foetal-derived cells, on the other hand, are generalists and do not form into memory cells. They respond to inflammatory signals and activate faster than adult T cells, allowing them to provide a broad swath of protection against pathogens they don't specifically recognise, Rudd said."It's the way that the immune system hedges its bet: It has cells that can respond at different rates," Rudd said.