Cytokines are signal molecules that induce movement, differentiation, growth and death of many cell types. Cytokines generate these effects through interactions with receptors, which relay a signal into the cell triggering a response.Cytokine-receptor interactions are promiscuous; a combining site of any receptor can bind many ligands. Promiscuity allows for the generation of agonists, alternative ligands that activate a receptor in a way similar to the normal ligands and antagonists, ligands that bind to a receptor, but neutralize the effects of an agonist. Cytokinereceptor interactions induce many diverse (pleiotropic) effects. Cytokine-receptor interactions are redundant; several cytokines can perform the same function.Mammalian hosts use cytokines to maintain homeostasis and to provide signals crucial to host responses to invading microbes and other injurious agents. Cytokines are the molecular messages, which: 1) initiate and amplify inflammatory and immune responses by recruiting and activating cells; 2) regulate the activation and differentiation of T-and B-lymphocytes, whose functions are crucial to specific cell-mediated immunity; and 3) initiate and regulate local repair processes critical to the resolution of inflammatory responses.Further studies of cytokines and their receptors should provide a framework for therapeutic interventions in patients with dysregulated inflammatory responses. Eur Respir J 2001; 18: Suppl. 34, 3s-17s. A review of cytokines and the lung is a daunting task. The scope of cytokine biology is immense since these molecules have wide-ranging biological effects. More than 190,000 citations that index cytokines have been published in the last decade and w1,800 cytokine manuscripts were published in the past month. A definition of "cytokines" is not simple; most textbooks and reviews do not provide such a definition. For the purpose of this review, cytokines will be defined as a diverse group of protein signal molecules that are produced by a wide variety of cells. Cytokines influence or activate adjacent cell movement, differentiation, growth and death. Cytokines generate these effects through interactions with receptors already present in low density on the cell surface or through upregulation of new receptors. Cytokine receptors relay a signal into the cell triggering a response. Regulation of receptor expression is as important as regulation of cytokine production if pulmonary homeostasis is to be maintained. Networks of cytokines act cooperatively to control normal physiological activity and disease-related threats to homeostasis. Furthermore, the composition of the cytokine milieu changes as disease processes progress and during resolution, remodelling and healing responses. Characteristics of cytokine-receptor interactions PromiscuityThe binding of cytokine ligands to cytokine receptors is promiscuous. A binding site of a receptor can bind many ligands and a ligand can bind several receptors. Molecular specificity hinges on the array of noncovalent bonds formed at t...

Rapid identification of pathogens in patients with bacterial pneumonia is important for optimal antimicrobial therapy. Coagglutination was compared with counterimmunoelectrophoresis (CIE) for sensitivity and specificity in the detection of Streptococcus pneumoniae, Hemophilus influenzae, Klebsiella pneumoniae, and Pseudomonas aeruginosa antigens in sputum specimens of 101 patients with community-acquired pneumonia. Coagglutination detected the appropriate bacterial antigen in 16 of 17 (94%) definite etiology patients and CIE detected 11 (64%). In 17 probable etiology patients, bacterial antigens were detected by coagglutination in 15 (88%) and by CIE in 7 (41%). Only 1 pathogen was falsely identified in the 19 culture-negative control patients, indicating a high degree of specificity for both tests. Coagglutination was more sensitive than CIE (p less than 0.05) or sputum stained with Gram's stain (p less than 0.05) in correctly identifying the putative pathogen in sputum. Our results strongly suggest that coagglutination is a useful diagnostic technique for establishing a rapid etiologic diagnosis in community-acquired pneumonia.

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