Background:

Interleukin 1 receptor type II (IL1R2), also known as CD121b, is a transmembrane protein and member of the IL-1 receptor family. It is found on B lymphocytes, neutrophils, monocytes, large granular leukocytes and endothelial cells. Like IL1R1, IL1R2 can bind all three forms of IL-1 (IL-1α, IL-1β and IL-1RA) but does not transmit IL-1 signals (1). In addition to the membrane-bound form, IL1R2 also exists as the soluble form and either acts as a decoy receptor that inhibits IL-1 action by blocking the binding of IL-1 to the type I receptor complex (2). Furthermore, IL-4 is reported to antagonize the activity of IL-1 by inducing the expression and release of IL1R2. Recombinant soluble IL1R2 is thus a potent antagonist of IL-1 action and serves as a potential therapeutic target (3). IL1R2 is involved in the control of the pro-inflammatory state that takes place in the endometrium during the premenstrual and menstrual periods. IL1R2 can neutralize IL-1β and counteract its effect on endometrial stromal cells, and therefore may provide a new clinical strategy for the treatment of endometriosis (4).