Cytokines and Inflammation

Abstract

Virtually all of the cytokines mediate biological activities either directly on immune cells or upon the adhesion molecules with which immune cells interact and may therefore be considered pro-inflammatory. Several cytokines, including tumor necrosis factor (TNF), interleukin (IL)-1, IL-6, and members of the small cytokine family, are uniquely capable of promoting the cellular infiltrate and damage to resident tissue that are characteristic of inflammation. The biology and techniques for the assay of these cytokines are described. Bioassays provided the earliest methods available to characterize cytokines. While potentially more sensitive than immune-based assays, bioassays may not be able to distinguish between cytokines with cross-reacting activities. In addition, bioassays may be falsely negative in the face of inhibitors, It remains useful, however, to assay cytokines by their biological activity. ELISAs will not differentiate biologically active from inactive but immunoreactive forms of the proteins. Since bioassays will detect only functional activity, they may be useful for identifying cytokine antagonists in a reaction mixture. The molecular cloning of cytokine cDNAs and the development of large-scale expression methods have made available virtually unlimited quantities of protein for biological assays. Purified proteins have also been used to develop immune-based assay techniques such as ELISAs for quantifying cytokines. ELISAs provide the best and in many cases the only mechanism for distinguishing cytokines with significant overlapping biological activities. The isolation of cytokine-specific cDNAs permits the use of molecular techniques to identify cytokine-specific mRNA transcripts. An extremely sensitive technique for detecting transcripts is the RNA-based polymerase chain reaction (RT-PCR). Biological assays for IL-1, IL-6, IL-8, and TNF are well standardized and are described here. The general techniques for the ELISA and RT-PCR are also described.