Tristetraprolin (TTP) is involved in the physiological regulation of the secretion of at least two important cytokines, tumor necrosis factor alpha (TNF) and granulocyte-macrophage colony-stimulating factor (GM-CSF). TTP exerts its effects by directly binding to the mRNAs encoding these proteins and destabilizing them, resulting in less secretion. Conversely, TTP deficiency results in an excess of both cytokines, leading to a systemic inflammatory syndrome. This invention include three categories of reagents related to TTP:1) Plasmid DNAs and mammalian expression vectors for human and mouse TTP; 2) Antibodies (rabbit antisera) to human and mouse TTP; 3) Immortalized macrophage cell lines derived from TTP-deficient mice and their wild-type littermates.