Immunologic proteins, usually made from immunoglobulins, that are capable of binding to, and rendering inactive, foreign substances that have entered the skin envelope and have been deemed dangerous. They may be synthesised anew in the presence of a previously encountered substance (antigen); they may be present in small amounts at all times in the bloodstream; or they may be present in the tissues in a more primitive form designed to react to a broad spectrum of potential antigens. The latter may be responsible for some allergies.