Assessment of Apoptosis in Xenobiotic-Induced Immunotoxicity

Generation of immunity is a highly complex process in which proliferation a nd differentiation of immune-competent cells regulated by cytokines and cel l-cell interactions play a major role. Reducing the number of immune-compet ent cells or altering the function, selection, and differentiation of lymph ocytes after xenobiotic treatment may lead to serious adverse effects. Prog rammed cell death, or apoptosis, is a highly regulated process by which an organism eliminates unwanted cells without eliciting an inflammatory respon se. However, xenobiotics are also able to trigger unwanted apoptosis or to alter the regulation of programmed cell death. Cytological characteristics of apoptosis are generally different: from those seen in acute pathological cell death resulting from cell injury. The toxins, morphological character istics of apoptosis are unique including cell shrinkage, membrane blebbing, chromatin condensation, DNA fragmentation, disruption of the nuclear lamin a, nuclear fragmentation, and emergence of apoptotic bodies. It is now esta blished that apoptosis plays a critical role in both development and homeos tasis of the immune system: thymic selection, cytotoxicity, deletion of aut oreactive cells, and regulation of the size of the lymphoid compartment. As sessment of apoptosis relies on the morphological and biochemical modificat ions of the dying cells. As a rule, and because an apoptotic cell rarely di splays all of the characteristic apoptotic features, several criteria shoul d be monitored in parallel including morphological examination. The techniq ues described in this paper have been divided into five categories: analysi s of cell morphology by microscopy, identification of DNA fragmentation, de termination of mitochondrial membrane potential, detection of plasma membra ne, changes, analysis of caspase activation. (C) 1999 Academic Press.