What time of day it is could influence whether or not we get an infection. A protein known to be involved in the immune system may be influenced by the body's circadian rhythm, according to researchers at Yale University in the USA.
Toll-like receptor nine (TLR9) is a protein expressed on cell membranes and known to play a vital role in recognition of pathogens, helping the body to detect new infections early.
Our daily 24-hour routine is determined by the circadian clock - a genetic mechanism that regulates sleep cycles and metabolic changes.
This study, published in the journal Immunity, showed that the amount and activity of TLR9 changed throughout this 24-hour cycle. The researchers found that the immune system response was improved if mice were infected at the point when TLR9 was most active.
'It does appear that disruptions of the circadian clock influence our susceptibility to pathogens', said lead researched Professor Erol Fikrig.
He added that this could have 'important implications for the prevention and treatment of disease'.
The work suggests that sufferers of jet lag (when the natural circadian rhythm gets out of sync after flying into a different time zone) could be more at risk of infections.
'People intuitively know that when their sleep patterns are disturbed, they are more likely to get sick', said Professor Fikrig.
Dr Akhilesh Reddy, a Cambridge University researcher investigating circadian rhythms, explained that the link to immunity has been known for a long time, but this is 'one of the first forays' into understanding why this is the case.
Dr Reddy added that some drug companies are 'now screening drugs at different times of the day' as they could potentially become more effective as the immune system cycles through more active phases.
This study was carried out in mice, so it is not known if there will be a similar link in humans. However it has previously been proposed that humans may be more susceptible to injury at certain times, for instance patients with sepsis (blood poisoning) are known to be at a greater risk of death between 2am and 6am.
Dr Reddy predicted that the circadian clock could play an important a role in medicine 'within 10 years'.