London: Heart attacks that mostly happen in the morning tend to be more severe than cardiac arrests at night, warn researchers.\r\n\r\nThe study, published in the journal Trends in Immunology, discusses how time of the day affects severity of afflictions, ranging from allergies to heart attacks. For example, studies showed that adaptive immune responses -- in which highly specialised, pathogen-fighting cells develop over weeks -- are under circadian control. \r\n\r\nResearchers compiled studies, predominantly in mice, that looked at the connection between circadian rhythms and immune responses. "This is 'striking' and should have relevance for clinical applications, from transplants to vaccinations," said study senior author Christoph Scheiermann, Professor at the University of Geneva in Switzerland. \r\n\r\nAccording to researchers, in both humans and mice, the numbers of white blood cells also oscillate in a circadian manner, raising the question whether it might be possible one day to optimise immune response through awareness and utilisation of the circadian clock.\r\n\r\nFor the study, researchers looked into separate studies that compared immune cell time-of-day rhythms under normal conditions, inflammation and disease.\r\n\r\n"Investigating circadian rhythms in innate and adaptive immunity is a great tool to generally understand the physiological interplay and time-dependent succession of events in generating immune responses," said Scheiermann.\r\n\r\n"The challenge lies in how to channel our growing mechanistic understanding of circadian immunology into time-tailored therapies for human patients," Scheiermann remarked.