That certain time of day does make us more susceptible to infection as our body clock affects the ability of viruses to replicate and spread between cells. This has been revealed by new research from the University of Cambridge and published in the Proceedings of the National Academy of Sciences. This may help explain why shift workers, whose body clocks are routinely disrupted, are more prone to health problems, including infections and chronic disease.
The machinery and resources in our cells are hijacked when a virus enters our body and helps to replicate and spread throughout the body. The resources fluctuate throughout the day, in response to our circadian rhythms (our body clock). These rhythms control many aspects of our physiology and bodily function that ranges from our sleep patterns to body temperature, and from our immune systems to the release of hormones. These cycles are controlled by a number of genes.
Researchers at the Wellcome Trust-Medical Research Council Institute of Metabolic Science, University of Cambridge, compared normal “wild type” mice infected with herpes virus at different times of the day and measured levels of virus infection and spread. There was a controlled environment where 12 hours were in daylight and 12 hours were dark. They found that virus replication in the infected mice at the start of the day (equivalent to sunrise when these nocturnal animals start their resting phase) was ten times greater than in mice infected 10 hours into the day when they are transitioning to their active phase. The experiment was repeated in mice lacking Bmal1 and they found high levels of virus replication regardless of the time of infection.
Professor Akhilesh Reddy, the study’s senior author says the time of day of infection can have a major influence on how susceptible we are to the disease, or at least on the viral replication. Infection at the wrong time of day could cause a much more severe acute infection. Even the time of day that you receive the influenza vaccine can influence how effectively it works. They also found similar time-of-day variation in virus replication in individual cell cultures, without influence from our immune system. Every cell in the body has a biological clock that allows them to keep track of time and anticipate daily changes in our environment. The clock in every cell determines how successfully a virus replicates and when we disrupt the body clock in either cells or mice, they found the timing of infection no longer mattered and the viral replication was always high.
This would mean that shift workers that work some nights and rest some nights, have a disrupted body clock and are more susceptible to viral diseases. These are the people who would really benefit from receiving the annual flu vaccines.
Herpes viruses manipulate the molecular clockwork that controls our circadian rhythms, helping the viruses to progress. Our body clocks do appear to play a role in defending us from invading pathogens, and their molecular machinery may offer a new and universal drug target to help fight infection.
This research was mostly funded by the Wellcome Trust and the European Research Council.