Mannose-binding lectin (MBL) is one of the important serum proteins activating complement system through lectin pathway. It also participates in opsonization of infection agens, apoptosis and in modulation of inflammation. Its deficiency predisposes the patient to repeated respiratory infections and higher susceptibility to other infectious and autoimmune diseases. The role of MBL could be substituted by the other parts of the immune system and that is why the immunodeficiency in adult patients is not profound. Association of MBL deficiency with rheumatoid arthritis or systemic lupus erythematosus is known. The course of these autoimmune disease might be worsen by MBL deficiency.

        Key words: mannan (mannose) – binding lectin (protein) deficiency