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There is evidence that alveolar macrophages (AM) play a role in the clearing of Pneumocystis carinii from the lungs. To investigate the mechanisms involved in this process, we studied in vitro the induction of an oxidative burst by P. carinii in a cell line of macrophages (NR8383) and AM from normal rats. P. carinui was added to macrophage monolayers (106 cells), and the H202 produced after 4 h of incubation was measured. Both NR8383 macrophages and normal rat AM produced H202 in response to P. carinii cysts and trophozoites isolated from dexamethasone-treated rats, although the amount of H202 induced in AM from normal rats was larger. NR8383 macrophages bound and phagocytized both P. carinii cysts and trophozoites and produced increasing amounts of H202 as a dose-related response to cysts and trophozoites. Opsonization ofP. carinii with normal rat serum increased H202 production by both types of macrophages; this enhancement was decreased, but not abolished, when the serum was first depleted of complement by heat treatment. These findings demonstrate that NR8383 macrophages and normal rat AM produce an oxidative burst in response to P. carinii and that this response is enhanced by complement.

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The uptake of cadmium by isolated liver cells was linearly related to the cadmium concentration to which the cells were exposed in the medium. Cadmium-treated cells synthesized proteins de novo with the characteristics of cadmium-thionein induced in the liver ofcadmium-treated animals. Thionein from liver cells incorporated cadmium and[35S]cysteine, had a Vl/Vo (Sephadex G-50) of 1.8-1.9, and was separated into two subfractions by DEAE-cellulose ion-exchange chromatography. Cycloheximide and actinomycin D when added after a cadmium exposure prevented the synthesis ofthionein. However, addition of actinomycin D after synthesis had started only decreased the total amount of thionein synthesized. The concentration of cadmium to which the cells were exposed affected the amount of cadmium-thionein synthesized in 6h. The maximum response occurred when cells were exposed to 0.5,ug of cadmium/ml; at higher metal concentrations the total amount of cadmium-thionein synthesized declined. The system described in the present paper can be used to study the mode of metal toxicity and the mechanism of cadmium-thionein synthesis.