 Peter Pickkers and his PhD student Matthijs Kox of the Radboud University Medical Center in the Netherlands took blood samples from Hof before and after his regimen of breathing, meditation and an 80-minute full-body ice bath, and found that afterwards he had reduced levels of proteins associated with the immune response.Pickkers and Kox injected him with an endotoxin that normally would stimulate a rapid immune response.Most subjects responded with flu-like symptoms (fever, headaches and shivering), with affected cells releasing signalling proteins called cytokines.