Carrageenan, a high molecular weight, sulfated polygalactose known to be toxic for macrophages in vitro was utilized in in vivo experiments to further study the role of this cell type in the initiation and expression of delayed hypersensitivity. When administered intraperitoneally to sensitized guinea pigs around the time of skin testing, carrageenan suppressed the expression of existing delayed hypersensitivity reactions to BSA. In addition, when administered at the time of immunization, carrageenan suppressed the development of subsequent delayed hypersensitivity. Carrageenan, in vitro did not appear to be cytotoxic for lymphocytes either structurally or functionally. It did not possess mitogenic properties and did not interfere with phytohemagglutinin induced lymphocyte transformation.
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