regulation of type IV hypersensitivity

Definition

Target type: biologicalprocess

Any process that modulates the frequency, rate, or extent of type IV hypersensitivity, a type of inflammatory response. [GOC:add, ISBN:0781735149]

Type IV hypersensitivity, also known as delayed-type hypersensitivity (DTH), is a cell-mediated immune response that develops over 24-72 hours after exposure to an antigen. This response is characterized by the activation of T lymphocytes, primarily CD4+ T helper 1 (Th1) cells, which release cytokines like interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α). These cytokines, along with chemokines, recruit and activate macrophages, leading to tissue damage. The process can be summarized in the following steps:

1. **Sensitization:** Initial exposure to an antigen, usually a protein, triggers a primary immune response. Antigen-presenting cells (APCs), such as dendritic cells (DCs), phagocytose the antigen and process it into peptides. These peptides are presented on MHC class II molecules to naïve CD4+ T cells in lymph nodes.
2. **Activation of Th1 cells:** The interaction between the antigen-MHC complex and the TCR on CD4+ T cells, along with co-stimulatory signals (CD80/CD86 on APCs and CD28 on T cells), leads to the activation and differentiation of naïve CD4+ T cells into Th1 cells. Th1 cells produce IFN-γ and TNF-α.
3. **Memory T cell formation:** Some activated Th1 cells become memory T cells, which reside in the lymph nodes and can rapidly respond upon subsequent exposure to the same antigen.
4. **Re-exposure and effector phase:** Upon re-exposure to the antigen, memory T cells migrate to the site of antigen presentation, where they encounter the antigen presented on APCs.
5. **Cytokine release and macrophage activation:** The interaction between the antigen-MHC complex and the TCR on memory T cells triggers the release of IFN-γ and TNF-α. These cytokines activate macrophages, leading to the recruitment of other inflammatory cells, such as neutrophils. Activated macrophages release a variety of pro-inflammatory mediators, including reactive oxygen species, proteases, and lysosomal enzymes, which cause tissue damage.
6. **Tissue damage:** The accumulation of inflammatory cells and the release of pro-inflammatory mediators result in tissue damage, which manifests clinically as inflammation, redness, swelling, and induration.

In summary, type IV hypersensitivity is a complex immune response involving the activation of Th1 cells, the release of pro-inflammatory cytokines, and the activation of macrophages, leading to tissue damage. This process is important in host defense against intracellular pathogens, but it can also contribute to the pathogenesis of various autoimmune diseases and allergic reactions.'
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Proteins (1)

Compounds (11)