Savvy Cytokines

Date: October 27, 1997 Comparison Chart Chart 2 The physiologic function of the immune system is simplistically viewed as a method to specifically respond and eliminate an initiating antigen. This process is mediated by a network of specialized cells and depends upon a pathway involving recognition, activation, differentiation and response of lymphocytes. This simplistic view is significantly more complicated when one is examining the biological nature of this response in greater detail. Not only are the specific front-line cells activated, but also a series of effector mechanisms is potentiated by antigenic stimulation that elicits a larger host response. These effector mechanisms are generally mediated by a group of proteins called cytokines. For activated T lymphocytes, these molecules are termed lymphokines. Some T cells produce cytokines to regulate lymphocyte activation, growth, and differentiation, while other T-cell populations principally function to activate and regulate inflammatory cells. These T cell-derived cytokines are consequently essential effector molecules of cell-mediated immunity, as well as bridges between the immune and inflammatory systems. Early studies on cytokines primarily employed bioassay-based studies which lead to a general understanding and description of the role of cytokines in responses such as macrophage activation and fever production. From these observations, and armed with better research tools, the next phase of research involved the partial purification and characterization of many of these unique proteins. During this phase of investigation that it was observed that many cytokines were principally synthesized by leukocytes and that many of their target responses were on other leukocytes. For this reason, this class of cytokines were named interleukins. With the advent of cloning and expressing individual cytokines, the ability of generating highly purified proteins allowed a greater understanding of the physiological mechanisms of action. Not only was it now able to structurally understand these molecules, but also these tools allowed researchers to identify and investigate their mechanisms of action cellular receptors. Assays which detect and quantitate cytokines have several significant implications for both basic and clinical research laboratories. Now approaching several decades of in vitro research, scientists have a tremendous knowledge base for these molecules. Yet a significant gap remains between this understanding and that of the in vivo mechanisms of action. The pathways of actions are now understood to be tremendously complex; a series of cascades of multiple downstream factors and responses is initiated. Therefore, there is a significant utility for such assay in the basic research lab. Bridging basic and clinical research, certain cytokines have been characterized with regard to specific disease states. That is, endogenous levels of specific or groups of cytokines will be either found to be elevated or depressed for a given disease. For example, IL-8 has been found to become elevated following injury or bacterial infection. Additionally, assays that quantitate cytokine levels, provide clinicians with a tool to potentially manage or modify the immune response in a predictable manner to influence the course of disease or therapy. These assays can be used to evaluate in vivo levels of cytokines in response to chemotherapeutic agents as a measure of disease status and patient response, and as an indicator in order to achieve a desired outcome. Under the general heading of cytokines, you will find that researchers have generated a number of letters, numbers, and Greek characters in an attempt to take into account a continually growing list of proteins. Many cytokines are also called chemokines, while many may be generically called factors. In order to simplify this enormous list and avoid generating an impractical table that might include proteins in multiple categories, LabConsumer asked companies to provide a list of assays for members of the interleukin family of cytokines. Historically, most interleukin assays have been ELISA-based, although several manufacturers provide kits for immunohistological formats. ELISA assays are typically in an antigen-capture format: plates are precoated with antibodies specific for a given interleukin. Detection methodologies employ a secondary antibody against the molecule that has been either directly conjugated with a reporter enzyme or for higher sensitivities, biotinylated for a secondary amplification of the signal. A number of companies now also provide DNA-based kits for the detection and quantification of message transcripts (Pharmingen). With this format, cytokine assays have entered the world of molecular biology. These assays are primarily targeted for basic research applications, where speed (time after activation) and sensitivity become an issue. These assays unfortunately do not have the simplicity of the ELISA format, but this is a problem with any DNA-based assay. The world of cytokines is large and complex. The numbers cytokines, and cytokine classes such as interleukins, will clearly increase in the future. Fortunately, the chore of developing an in-house assay has been replaced with convenient assays and kits. The primary advantage of these kits is the uniform sensitivity that is seldom achieved in the "home-brewed" assays. It will pay to take a look at the product offerings from these companies. Additionally, you should not hesitate contacting the technical support staff to ask specific questions regarding your applications. Comparison Chart Chart 2 Thomas F. Unger is Vice President for Research and Development for Miragen Inc, an Irvine, California based biotech company. He can be reached at tfunger@aol.com.

Savvy Cytokines

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