Regulation of delayed-type hypersensitivity-like responses in the mouse lung, determined with histological procedures: serotonin, T-cell suppressor-inducer factor and high antigen dose tolerance regulate the magnitude of T-cell dependent inflammatory reactions.

We have studied delayed-type hypersensitivity (DTH) responses to picryl chloride (PCl) in the lungs of mice. Intranasal challenge with 0.6% picryl sulphonic acid (PSA), a water soluble form of PCl, of BALB/c mice, sensitized with PCl epicutaneously 1 week earlier, induced an accumulation of mononuclear inflammatory cells around bronchioli and blood vessels. Maximal inflammatory responses were seen 48 hr after challenge. These responses were antigen-specific, and also T-cell dependent, since athymic nude mice failed to show this reaction. A role for mast cells in the responses was studied using two strains of mast cell-deficient mice. In one of these (W/Wv) lung DTH responses to PCl were reduced severely. In the other strain (S1/S1d) the responses around vessels were decreased slightly, whereas the responses in the interstitial tissue and around bronchioli were similar to those in +/+ littermate controls. Involvement of serotonin was investigated using two serotonin receptor antagonists, i.e. methysergide and ketanserin. Treatment of mice with either of the antagonists prevented occurrence of the DTH-like reaction in the lung after intranasal antigen challenge. In the lungs of sensitized mice, significantly increased permeability was established 2 hr after antigen challenge. It was concluded that release of serotonin in the lung may provide an environment that comprises local vascular permeability and that facilitates the local recruitment and possibly the activation of DTH effector T cells, leading to subsequent attraction of mononuclear leucocytes into the lung. Immunological regulation of the DTH-like reactions in the lung was similar to that of contact sensitivity in the skin, since intravenous injection of an antigen-specific T-cell suppressor inducer factor prior to sensitization or pretreatment with a high dose of picryl sulphonic acid intravenously both resulted in reduction of the DTH-like lung histological response to picryl sulphonic acid. From these findings it was concluded that DTH-like lung responses are similar to DTH responses in the skin.