Heterotetramer composed of two non-covalently linked disulfide-linked heterodimer of chains 1 and 2. Experimental confirmation may be lacking for some isoforms. The long form is preferentially expressed in the salivary gland, while the short form is preferentially expressed in the skin. Causes an allergic reaction in human. Binds to IgE. Major allergen produced by the domestic cat. Implicated as an asthma-inducing agent in human. This protein is sticky and easily adheres to walls, carpet, clothing, furniture and bedding. Belongs to the secretoglobin family.