Abstract
Sublethal whole-body irradiation in the guinea pig had little demonstrable effect on the development of delayed hypersensitivity but caused a profound, though transient depression of dermal reactivity in previously sensitized animals. Macrophage-rich peritoneal cell suspensions from non-sensitive donors when injected intradermally with eliciting antigen, resulted in the restoration of a significant degree of reactivity following irradiation. Inocula of lymphocytes, on the other hand, failed to yield similar results. These findings, when taken with the persistence of low levels of reactivity following irradiation and the ability to transfer reactivity with peritoneal exudate cells from animals so treated, warrant the conclusion that the presence of macrophages is necessary for the expression of cutaneous delayed hypersensitivity. The spontaneously renewed activity which follows the depressed phase is thus more of a reflection of the recovery of macrophage precursors from radiation injury, rather than the emergence of a new population of sensitized cells. The results, in addition, substantiate the belief that the expression of delayed hypersensitivity requires at least two cell populations, only one of which carries the property of specificity at the outset. The presence of the sensitized population cannot always be excluded by a weak or absent skin test.
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