A team of South Korean scientists has made a possible breakthrough in fighting chronic viral diseases, identifying for the first time in the world a micro RNA that gives viruses stealth-like functions to avoid attacks by the human immune system. The team, led by Prof. Ahn Kwang-seok of Seoul National University, has confirmed that micro RNA US4 prevents human T cells, also known as killer cells, from identifying viruses, and thus allowing viruses to survive long enough in human bodies to cause chronic diseases, the Ministry of Education, Science and Technology said Tuesday. It is the first time micro RNA US4 has been identified, along with its functions, according to the Seoul National University professor. The research was conducted by the school\'s two doctoral program students -- Lee Sang-hyun and Kim Seong-cheol -- under Ahn\'s supervision. Their paper, titled \"Human cytomegalovirus microRNA miR-US4-1 inhibits CD8+ T cell responses by targeting the aminopeptidase ERAP1,\" was published Sunday on the Web site of Nature Immunology, a sister journal of the science magazine Nature. \"The findings are significant in that they suggested a new way of treating chronic viral diseases, which has so far been unsuccessful,\" Ahn told Yonhap News Agency by phone. \"This (failure) is because research currently focus on the protein produced by viruses, but the study shows we should focus on micro RNA inside the viruses.\" Ahn said T cells from persons with chronic viral diseases began to effectively attack viruses as soon as micro RNA US4 of the viruses were eliminated in lab tests. Micro RNA can be effectively eliminated, for instance, by injecting an RNA with a DNA sequence that is the exact opposite of the target RNA, he added.