Basic science for the clinician 28: T-helper cell subtypes

The immune response is finely tuned to the various invaders that may cause damage and disease. There is an innate immune system and an acquired immune response, but there is much overlap and recruitment across these lines of demarcation. Broadly speaking, there are cellular immune responses (cellular effectors that identify intracellular pathogens and damage and kill the affected cell) and humoral (B cells become plasma cells which make antibodies to bind extracellular pathogens and their products) that draw upon both systems. At the pivotal point, where decisions are made whether to mount a primarily cellular or a humoral response are T-helper cells (CD4). As you may have read, CD4 cells come in at least 2 subtypes: TH1 cells predispose to the development of a primarily cellular responses and TH2 predispose to humoral responses. Not very complicated, but worthy of some discussion to look at the cytokines produced, the changes these cytokines evince, and how the balances (dare I say yin and yang) keep us healthy but also may get us into trouble!