TNF is a cytokine, a protein, that is produced by white blood cells due to the body's natural immune system response. If an individual has an autoimmune disorder such as rheumatoid arthritis or psoriasis this protein may become elevated as the immune system is attacking healthy cells or other body parts (joints, or skin for example) by mistake.

Due to the significant proinflammatory and immunoregulatory functions of TNF-alpha, and the wide distribution of TNFRs, the deregulation TNF-alpha is associated with the development of several immunologic disorders and prediction of disease outcomes.

Indeed, elevated levels of TNF-alpha in serum or plasma levels have been able to predict severity in some infectious diseases such as sepsis in bacterial infections or poor outcomes in coronavirus 2019 infections. 

In addition, TNF-alpha has been implicated in post-transplant reactions, pathological mechanisms in certain autoimmune diseases (eg, rheumatoid arthritis, inflammatory bowel disease, ankylosing spondylitis), and cancers.

References:

Idriss HT, Naismith JH. TNF alpha and the TNF receptor superfamily: structure-function relationship(s). Microsc Res Tech. 2000 Aug 1;50(3):184-95. doi: 10.1002/1097-0029(20000801)50:3<184::AID-JEMT2>3.0.CO;2-H. PMID: 10891884. [L]