Pathologic Ab-Ig Proteins are immunoglobulin-related (IgA, IgD, IgE, IgG, IgM antibody) glycoproteins characteristically found in patients with multiple myeloma, infectious diseases, rheumatoid arthritis and other connective tissue diseases, or systemic autoimmune diseases including systemic lupus erythematosus, Sjogren's syndrome, scleroderma, polymyositis, and mixed connective tissue disease. [ ]