ROS and RNS are normally produced by these cells to fight infection. ROS, alone, cause more than 20 types of DNA damage. Oxidative DNA damages cause both mutations and epigenetic alterations. RNS also cause mutagenic DNA damages.A normal cell may undergo carcinogenesis to become a cancer cell if it is frequently subjected to DNA damage during long periods of chronic inflammation. DNA damages may cause genetic mutations due to inaccurate repair. In addition, mistakes in the DNA repair process may cause epigenetic alterations. Mutations and epigenetic alterations that are replicated and provide a selective advantage during somatic cell proliferation may be carcinogenic. Genome-wide analyses of human cancer tissues reveal that a single typical cancer cell may possess roughly 100 mutations in coding regions, 10-20 of which are "driver mutations" that contribute to cancer development. However, chronic inflammation also causes epigenetic changes such as DNA methylations, that are often more common than mutations. Typically, several hundreds to thousands of genes are methylated in a cancer cell (see DNA methylation in cancer). Sites of oxidative damage in chromatin can recruit complexes that contain DNA methyltransferases (DNMTs), a histone deacetylase (SIRT1), and a histone methyltransferase (EZH2), and thus induce DNA methylation. DNA methylation of a CpG island in a promoter region may cause silencing of its downstream gene (see CpG site and regulation of transcription in cancer). DNA repair genes, in particular, are frequently inactivated by methylation in various cancers (see hypermethylation of DNA repair genes in cancer).
Prolonged inflammation, known as chronic inflammation, leads to a progressive shift in the type of cells present at the site of inflammation, such as mononuclear cells, and is characterized by simultaneous destruction and healing of the tissue from the inflammatory process. Inflammation has also been classified as Type 1 and Type 2 based on the type of cytokines and helper T cells (Th1 and Th2) involved.Inflammation is not a synonym for infection. Infection describes the interaction between the action of microbial invasion and the reaction of the bodys inflammatory response—the two components are considered together when discussing an infection, and the word is used to imply a microbial invasive cause for the observed inflammatory reaction. Inflammation, on the other hand, describes purely the bodys immunovascular response—whatever the cause may be. But because of how often the two are correlated, words ending in the suffix -itis (which refers to inflammation) are sometimes informally described as referring to infection. For example, the word urethritis strictly means only "urethral inflammation", but clinical health care providers usually discuss urethritis as a urethral infection because urethral microbial invasion is the most common cause of urethritis. However, the inflammation-infection distinction becomes crucial for situations in pathology and medical diagnosis where inflammation is not driven by microbial invasion, such as the cases of atherosclerosis, trauma, ischemia, and autoimmune diseases (including type III hypersensitivity). Causes
Types
Acute
Acute inflammation occurs immediately upon injury, lasting only a few days. Cytokines and chemokines promote the migration of neutrophils and macrophages to the site of inflammation.