Cystatins are small human proteins that mainly function as protease inhibitors and are found throughout the body. Proteases are enzymes that begin to break down proteins. They can function intracellularly and extracellularly in order to inhibit their target cysteine enzymes (Ochieng, 2010). This allows the proteins to maintain the balance of protease inhibitors versus the proteins and regulate any damaging activity by the proteases. By sustaining the balance between proteases and cystatins found in the body, immunomodulatory functions, which are any factors that cause change within the normal immune system, not related to protease inhibition, can be regulated. This is very important because impairment in inflammatory responses can cause …show more content…
Tissues break down by the degradation of the extracellular matrix, which promotes excessive immune cell leakage to inflammation sites and enhances organ damage. The roles of most cystatins are not clearly defined or known; however, these proteins have been found to have secondary functions. For example, as stated in this article by Eaves-Pyles in 2013, cystatins C and B have were found to have anti-tumor effects that decreased the rapid cell growth and metastasis of a tumor. Along with this function, Cystatin C has shown an ability to protect the neuronal functions, which could lead to promising new therapies for neurodegenerative disorders, such as Alzheimer’s Disease. Cystatin B possesses antiviral properties as it has been shown to decrease HIV replication in macrophages (Eaves, 2013). There is no known secondary function of cystatin 9, but researchers discovered surprising functions of the protein due to an infection within the lungs. This lung infection was a result of the bacteria, Francisella tularensis (Ft). Ft is a pathogenic species of gram-negative, aerobic bacteria that has been found to be the major cause of tularemia. Tularemia is an airborne disease that is often associated with the bodies