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The effect of a single exposure to Cd on DH was studied through exposure to Cd at different time intervals in relation to antigen administration. Exposure to Cd significantly suppressed the DH reaction, with a dose-response relationship, when administered 2 or 3 days after immunization of BALB/c and DBA/2 mice with sheep red blood cells. A strain difference in sensitivity to Cd was also demonstrated. These results suggest that a single exposure to Cd impairs the cellular immune response in mice.

1. Repeated injections of zinc (Zn) and copper (Cu) into the frog Xenopus laevis caused accumulations of the respective metals in the liver and kidney. 2. The accumulated metals in the liver supernatant fractions were present as Zn- and Cu-binding proteins of the same properties as that of metallothionein (MT) induced by cadmium (Cd) injections. 3. The affinity of Zn, Cu and Cd ions to the metal-binding protein was in the decreasing order of Cu, Cd and Zn. 4. The Xenopus MT induced by Cd was unstable and disrupted easily to give two peaks as if the MT consists of two isometallothioneins.

A low-Mr copper (Cu) and zinc (Zn)-binding protein was present in the liver of a control water lizard Triturus pyrrhogaster. Cadmium (Cd) accumulated in the liver of the animals after intramuscular injections of Cd salt and was bound to Cu- and Zn-binding protein of a single isoform that had properties characteristic of metallothionein (MT). Effects of Cd loading on several essential elements in the liver and kidney were also determined.

Effects of a single intraperitoneal (i.p.) injection of cadmium (Cd) on the primary humoral antibody responses against sheep red blood cells (SRBC) in mice were studied by assaying splenic plaque forming cells (PFC). PFC responses in mice were suppressed when exposed to Cd 2 days after immunization, and inconsistently stimulated when exposed before immunization. Dose-response relationships were observed in the suppressive effect of Cd exposure 2 days after immunization, but not consistently in the stimulative effect of Cd exposure before immunization. Thymus weights and cell numbers decreased markedly 4 days after Cd exposure with or without the antigenic stimulus. Splenic weights increased 2 days after Cd exposure, while the number of spleen cells was dramatically decreased 1 days after Cd exposure and still remained below normal 2 days after exposure.