The mast cells of the mammalian central nervous system. 2. The effect of proton irradiation in the monkey

Young adult monkeys (Macaca mulatta) were irradiated with protons variable in energy and dosage and given at different rates. They died or were killed at intervals and their brains and spinal cords were examined for several changes including the status of the mast cells (MCs) (see Ibrahim 1974). Depending on the animal and the dosage, initial changes in these cells included various combinations of partial or complete degranulation, anisogranulation, hypertrophy and moderate to marked increase in number. These changes are similar to changes recorded in the literature respecting MCs outside the CNS; they resolved, but incompletely, within a few days. When delayed radionecrosis occurred a few months later, the same changes recurred but generally more intensely and were sometimes accompanied by parenchymal perivascular or leptomeningeal mononuclear cell inflammatory infiltrates. Calcification and pigment transformation of some MCs occurred. Also, in 3 cases marked oligodendroglial proliferation in central white matter was seen accompanied by intense MC damage. This proliferation is of interest in relation to experimental and human demyelination. An aetiological relationship between MC changes and both early and delayed vascular and parenchymal damage is possible. The suggestion made by others, that many features of delayed radionecrosis are due to a delayed hypersensitivity reaction, is here reiterated, but in addition there seems also to be a possibility that the MCs are involved in providing the antigen either directly or indirectly. Vascular damage must be responsible for many features of delayed radionecrosis.