Interest in this phenomenon stopped in 1942 with the availability of antibiotics and the infusion of money to study the harmful effects of excess exposure to ionizing radiation. These reports indicate the effect of hormetic doses of ionizing radiation was less a deterrent to infection than an activation of host tissues. Similar differences in T cell reactions were found when young and old people from the high and low background areas of China were compared. Myeloid cells include several types of circulating white blood cells. Macrophages, or phagocytes, are important components of most tissues.
Macrophages search, identify, and engulf nonself intruders, including newly mutated cancer cells.
They scavenge dead cells, particulates, and other waste, and transport such material to lymph nodes for storage or further processing. Their proteinaceous messages, left on cells not digested, help leukocytes to react to these intruders. Cell mediated immune competence following whole-body exposure with single doses of 0.4 Gy in preimmunized mice has been studied extensively by the Hellstrom group. Immune protection is most effective for small, newly initiated tumors. The tumors grew well in control mice and those exposed to 5 Gy of X-rays.