​London, Oct 2 (IANS) Family history and environment of the residential area are responsible for the differences between individual immune systems, a study has found.

The study published in the journal Trends in Immunology, discusses what shapes our immune system and how it might be applied.

The study has shown that air quality, food, stress levels, sleep patterns, and lifestyle choices had a strong combined effect on immune responses.

"Diversity isn't just programmed into our genes -- it emerges from how our genes respond to the environment," said Adrian Liston, researcher at the Translational Immunology Laboratory, Belgium.

Long-term infections are responsible for most of the differences between individual immune systems. 

These interactions slowly change the cellular makeup of immune system and make it more sensitive to that specific virus but also easier for other infections to slip past its defences. 

"People without these infections don't experience these cellular changes and even with the occasional cold or fever, their immune systems stay relatively stable over time. The exception is when a person is elderly," Liston added.

Researchers have shown that ageing changes how our immune system responds to threats. 

According to the study, as one gets older an organ called the thymus gradually stops producing T cells, which are made to help to fight off infection. Without new T cells, older people are more likely to get sick and less likely to respond to vaccines.

Beyond T cells, ageing also seems to broadly change the way our immune systems react. 

"A lot of diseases that we associated with ageing have an inflammatory component, which suggests there is likely immune involvement," said Michelle Linterman, researcher at the Babraham Institute, Britain.

"Understanding how the immune system changes with age is going to be hugely important for treating age-related diseases in the future," Linterman added.