J Chain Immunoglobulins are a type of protein found in the immune system. They are also known as joining chain proteins. J Chain proteins help to hold and stabilize antibodies, which are proteins that recognize and mark foreign substances, such as bacteria and viruses, to be eliminated by the body.

J Chain proteins are produced mainly by B lymphocytes, which are the primary cells of the adaptive immune system. They are involved in helping B lymphocytes produce immunoglobulins, which are proteins essential in helping the body recognize and mark foreign substances. This helps the body to strengthen its defenses against infection.