All of Koch's postulates have been verified for the relationship between infectious mononucleosis and Epstein-Barr virus, a herpesvirus. However, the relationship between this virus and Burkitt's lymphoma, sarcoid, and systemic lupus erythematosus (SLE) is less clear. Infectious mononucleosis is most common in young adults (14 to 18 years of age) and is very rare in young children. There is no specific treatment. Heterophil antibody titer is helpful in diagnosis, but is not expressed as a function of clinical recovery.