Cytokine and cytokine receptor expression as a biological indicator of immune activation: important considerations in the development of in vitro model systems

Studies of the biological activity of T-lymphocytes in response to immune activation are often based on in vitro models using polyclonal activators such as anti-CD3 antibodies, pharmacological agents, like phorbol esters, and mitogens, like phytohemagglutinin. Activation of T-lymphocytes results in expression of cytokine receptors, production and secretion of cytokines, expression of cell surface activation markers, and cellular proliferation. This study reviews the most commonly used methods of in vitro activation by non-specific polyclonal activators on target populations of both isolated T-lymphocytes and mononuclear cells. The resultant biological activity was measured by expression of cell surface cytokine receptors, intracellular cytokine expression and quantitation of secreted cytokines. This study demonstrates the different results that can occur depending upon the nature of the population making up the responding cells, method of activation, and duration of culture. Special care must be taken when developing in vitro models of immune activation and interpreting the resultant biological activity. The results of the experiments reviewed here demonstrate the importance of measuring cytokine receptors and quantitating cytokine secretion in conjunction with identifying the cytokine-producing cells. Recent advances in flow cytometry technology permit analysis of all these parameters on a single platform. (C) 2000 Elsevier Science B.V. All rights reserved.