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Nasopharyngeal carcinoma (NPC) is one of the most commons cancers in Southeast Asia and Southern China. Several NPC-associated genes have been so far described and here we describe the identification and the characterization of a novel nasopharyngeal carcinoma-associated peptide: NAP-1. NAP-1 was identified with the human genome draft searching method combined with nested PCR mapping of the chromosome 4q13 region. NAP-1 encodes an 85 amino acid alkaline peptide with a calculated isoelectric point of 9.3, three phosphorilation sites and a proline-rich region. Northern blot analysis revealed that NAP-1 is expressed as a 0.6 kb transcript in normal lymph nodes and trachea. In addition, reverse transcription (RT)-PCR showed that NAP-1 is expressed not only in NPC but in normal nasopharynx (NP) and various other tumors and tissues of the head and neck including: tonsils, lymph nodes, carcinoma of the tonsil, T cell lymphomas, squamous cell carcinoma of the hard palate, papilloma of the nasopharynx, nasopharyngitis, lymphoma of the tongue root and follicular dendritic cells (FDC). In addition, NAP-1 is not expressed in normal tissues or tumors from other anatomical regions and was not expressed by NPC cell lines. Surprisingly, differential RT-PCR demonstrated decreased expression of NAP-1 in NPC compared with paired NP biopsies in 42.5 % of cases (17 out of 40). In addition, in situ hybridization and immunohistochemistry demonstrated that NAP-1 is expressed by S100+ CD35+ FDCs of the germinal center and not in other normal immune cells infiltrating NP or NPC. Therefore, it is likely that NAP-1 is secreted by FDC in the NP and may play an immune modulatory role in NPC. [ABSTRACT FROM AUTHOR]