The effect of X-ray irradiation on the adjuvant syndrome and the inflammatory response to urate crystals.

In rats, X-ray irradiation reduced the number of circulating leucocytes at different rates: mononuclears were depleted in 24 h, granulocytes were numerically reduced only 72 h after irradiation. The injection of adjuvant 24 h after exposure to X-rays resulted in inhibition of primary reactions at the injection site into one of the hind paws. Secondary reactions did not develop. Injected 72 h after irradiation, adjuvant evoked primary responses the severity of which was comparable to those of controls. Secondary lesions in the contralateral paw, forelimbs, ears and tail were detected which were less severe and developed at a later time than in controls. In contrast, normal responses to urate crystals were observed by injecting the irritant 24 h after irradiation. Injected 72 h after irradiation, urate crystals induced decreased inflammatory responses. Irradiation seemed to have interfered with the development of the response to adjuvant administered 24 h afterwards, by affecting lymphocyte subpopulations: the inhibition of the primary reaction presumably resulted from the numerical reduction of lymphoid cells characteristically distinct from B- and T-lymphocytes; reduced subpopulations of T and B-cells apparently accounted for the inhibition of secondary reactions. With the partial recovery from lymphocytopenia which started 4-5 days after irradiation, the animals could again respond with fully developed primary reactions to adjuvant injected 72 h after exposure to X-rays. Since secondary lesions in this group were less severe and developed at a later time than in controls, it is plausible that recovery from depletion of B- and T-lymphocyte subpopulations proceeded at a slower rate than recovery from depletion of non-B, non-T lymphoid cells responsible for the development of primary reactions. The experiments with urate crystals indicated that granulocytes were essential for the development of the acute oedematous response to this irritant. It is concluded that the relative contribution of lymphocytes and granulocytes for the development of inflammatory responses largely depend on the nature of the irritant employed.