Cellular side of acquired immunity (T cells)
The adaptive T-cell response represents the most sophisticated component of the immune response. Foreign invaders are recognized first by cells of the innate immune system. This leads to a rapid and non-specific inflammatory response, followed by induction of the adaptive and specific immune response. Different adaptive responses can be promoted, depending on the predominant effector cells that are involved, which themselves depend on the microbial/antigen stimuli. As examples, Th1 cells contribute to cell-mediated immunity against intracellular pathogens, Th2 cells protect against parasites, and Th17 cells act against extracellular bacteria and fungi that are not cleared by Th1 and Th2 cells. Among the new subsets, Th22 cells protect against disruption of epithelial layers secondary to invading pathogens. Finally these effector subsets are regulated by regulatory T cells. These T helper subsets counteract each other to maintain the homeostasis of the immune system, but this balance can be easily disrupted, leading to chronic inflammation or autoimmune diseases. The challenge is to detect early changes in this balance, prior to its clinical expression. New molecular tools such as microarrays could be used to determine the predominant profile of the immune effector cells involved in a disease process. Such understanding should provide better therapeutic tools to counteract deregulated effector cells.