Detection of Cytokine Signal Transduction Cross-Talk in Leukocyte Activation

Cytokines are a diverse group of proteins and glycoproteins that promote intercellular communication among leukocytes or between leukocyte and other cell types (1 ). Although most cytokines are soluble proteins, they can infrequently be found expressed at the cell surface. Cytokines are ligands for one or more cell surface receptors that mediate communication with intracellular signaling, metabolic, and gene regulation pathways. Cells respond to these intra-cellular signals by alterations in their growth, differentiation, or motility. However, during physiological activities, cytokines are not expressed individually, but rather as a variety of cytokine patterns. Factors that may contribute to cytokine expression patterns are: (a) their ability to be either stimulatory or inhibitory and (b) the presence of both positive and negative feedback pathways at many levels. It is likely that the tools of biocomplexity being developed for understanding the behavior of metabolic and neural networks will be also contribute to our understanding of cytokine networks in vivo (e.g., ref. 2 ).