Interacts with heparin. Highly expressed in the kidney, brain and testis and to a lower extent in heart, liver and small intestine (PubMed:15177561). Expressed in the lens, cornea and retina. Strongly expressed in the distal tips of the retinal neuroepithelium that form the iris and ciliary body (PubMed:27839872). Expressed early in development of the eye (week 9 to week 22 of gestation). Up-regulated by IL1B/interleukin-1 beta and IL6/interleukin-6. Proteolytically cleaved into 2 chains of about 70 and 130 kDa. The fragments are not connected by disulfide bonds. The disease is caused by variants affecting the gene represented in this entry. Belongs to the protease inhibitor I39 (alpha-2-macroglobulin) family. Truncated N-terminus.