T Cells and Inflammation
Lymphocytes from the so-called T helper cell (Th) lineage (characterised by the expression of the surface molecule CD4) play a central role in the initiation and maintenance of allergic and autoimmune inflammatory processes. They become activated by the presentation of antigen (i.e. allergen or autoantigen) by antigen-presenting cells such as dendritic cells or macrophages. Subsequently, antigen-specific Th cells proliferate and become activated.
Source: Akdis et al., JACI 2009 (modified)
A major feature of T cell activation is the production of mediators, so-called cytokines. Depending on the set of cytokines they produce, several Th subpopulations are discernible. For example, the marker cytokines of Th1 cells are interferon-γ(IFNy), interleukin (IL)-2 and tumor necrosis factors (TNF) whereas Th2 cells preferentially secrete IL-4, IL-5, and IL-13. By means of these cytokines different effector mechanisms of inflammatory responses are triggered that are characteristic for certain disease conditions, e.g. Th2 cells induce allergic inflammatory responses characterised by infiltration of eosinophil granulocytes whereas Th1 cells trigger the infiltration of neutrophil granulocytes to the site of inflammation.