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Cytokines are pivotal to a balanced innate or cell-mediated immune response, can be indicative of disease progression and/or resolution, and are being evaluated as therapeutics. There is a need to purify and/or to measure key cytokines rapidly with accuracy, precision, and sensitivity. The current assay technologies, which are based on RT-PCR, immunoassays, or bioassays, are limited in their use in the clinic, in particular because of the long time (1—3 h) required to carry out the assays. An alternative approach explored here is the use of pathogen-encoded cytokine- binding proteins, which have Kd in the nanomolar range. It is anticipated that pathogens have evolved binding proteins, antagonists, and/or specific neutralizing phenotypes directed against key signaling and effector molecules involved in the multifaceted host defense system. Thus, by screening the genomes of a wide range of microbial agents, we would expect to find coding sequences for binding proteins for the most important cytokines. Consistent with this view is the identification of poxvirus genes encoding binding activities for TNF, type I and type II interferons, interleukin (IL)-1β, IL-18, and β-chemokines. These high-affinity receptors have the potential to act as surrogate antibodies in a number of applications in cytokine quantification and purification and could be potentially useful reagents to complement the existing panel of anti-cytokine, monoclonal, polyclonal, or engineered antibodies that are currently available.