The mechanisms by which the inflammatory response is induced are not clearly understood. Neutrophils, which are found in blood but not in normal tissues are the earliest phagocytic cells to be recruited to the infection site. The four classic signs of inflammation, redness, heat, swelling, and pain result from increased capillary permeability, influx of phagocytic cells, and tissue damage. Factors that stimulate or control the inflammatory response in virus infection include soluble cytokine receptors expressed by some viruses, cytokines and growth factors whose expression is induced by viruses. Cytokines Cytokines are regulatory proteins that mediate essential processes in intercellular communication during an antiviral defense.
Many cells are capable of synthesizing cytokines but do so only under appropriate conditions.
Cytokines act by controlling inflammation, inducing antiviral state in infected cells, and regulating the adaptive immune response. They exert their activity by binding to specific receptors and activating gene expression in cells bearing these receptors. More than 35 cytokines are known. The IFNs are the most important cytokines in innate response against virus infection. Whereas the mechanism that triggers their production is not known, it is believed that accumulation of double-stranded RNA, an inevitable product of RNA and DNA virus replication, plays a key role.