The immune system uses the lethal effects of oxidants by making production of oxidizing species a central part of its mechanism of killing pathogens; with activated phagocytes producing both ROS and reactive nitrogen species. These include superoxide (•O −
2 ) , nitric oxide (•NO) and their particularly reactive product, peroxynitrite (ONOO-).  Although the use of these highly reactive compounds in the cytotoxic response of phagocytes causes damage to host tissues, the non-specificity of these oxidants is an advantage since they will damage almost every part of their target cell.  This prevents a pathogen from escaping this part of immune response by mutation of a single molecular target.
My life’s work has helped me to tell the story of stress, starting with the mentors for my dissertation, completed in 1964. These two Rockefeller University scientists, Vincent Allfrey and Alfred Mirsky, taught me the fundamentals of epigenetics in the 1960s, before there was much interest in it, and when epigenetics meant something quite different, namely, the emergence of characteristics as a fertilised egg developed into a living organism. Development from embryo to independence is programmed into each species, but the individual characteristics that emerge are influenced by experience, and that is where the modern use of ‘epigenetics’ comes from. An example of this is a pair of identical twins with genes that predispose them to schizophrenia or bipolar illness. Even with the same DNA, the probability that one twin will develop the disease when the other twin gets it is only in the range of 30-60 per cent, which leaves plenty of room for experiences and other environmental factors to either prevent or precipitate the disorder.