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Interleukin-1 (IL-1) was first described more than a decade ago as lymphocyte-activating factor (LAF) for its ability to costimulate mitogen-activated mouse thy-mocyte proliferation (Gery et al. 1971). Since this ini-tial observation, it has become clear that IL-1 has a number of other biological activities and that there are at least two major types of IL-1 proteins produced by activated macrophages and by other cell types. Some of the activities ascribed to IL-1 include the ability to stimulate B-cell function, fibroblast proliferation, muscle proteolysis, prostaglandin E2 (PGE2) and col-lagenase production by rheumatoid synovial cells, he-patic acute-phase protein synthesis, and to induce fever (for review, see Dinarello 1984). Although its activities are numerous and diverse, it has been suggested that
Lomedico et al. (Wed,) studied this question.