The term interleukin implies that a substance is produced by leukocytes and acts on leukocytes. The IL-n designation provides a way to classify many cytokines and cytokinelike molecules. But even a structure-based classification presents problems, as many cytokine structures have not been determined. Researchers are left to predict the most likely folds from sequence similarity. Because many cytokines and growth factors are now produced from cloned genes, purity is becoming less of an issue than it was in the past.
Many companies do, however, subject their protein and peptide products to extensive quality control.
Some companies provide products as lyophilized solutions and some add carrier proteins such as BSA or additives such as sucrose. Sometimes proteins are lyophilized with salts. Cytokines are the main mediators of immunity and inflammation and are involved with repair following both endogenous and external cell insults. Invasions from pathogenic microbes, insults from trauma, and progressive breakdown of normal cell processes such as during tumor formation all induce complex patterns of cytokine expression and action. 3,4 Cytokines, therefore, have become invaluable probes for studying the biology of the immune and inflammatory responses.