Role and development of Th1/Th2 immune responses in the lungs

The development of T helper 1 (Th1) and Th2 responses is dependent on the cells and early signals of the innate immune system. Following inhalation of pulmonary pathogens, lung antigen-presenting cells (APCs) ingest the microbe, begin to process antigen, and migrate to peripheral lymphoid tissues (i.e., LALNs). It is in the lymph node that the APC-T cell interaction takes place; therefore, the microenvironment of the lymph node significantly influences the developing T cell response (Th1 vs Th2). Several factors can determine the nature of the T cell response, including cytokines, chemokines, microbial virulence factors, and dendritic cell phenotype. A shift in the Th1/Th2 balance in the lungs can result in chronic infection, allergic disease, and immunopathology. This review discusses the mechanisms of developing Th1/Th2 pulmonary responses, the counterregulation of Th1/Th2 immunity, and the consequences of immune deviation in the lungs.