The monoclonal antibody 8C8 recognizes human alpha-defensin 5 (HD5). HD5 is an antimicrobial peptide produced by Paneth cells, specialized epithelial cells of the small intestinal crypt. HD5 is stored in the Paneth cells as propeptide (aa 20-94) and released as mature peptide after trypsin digestion, which is co-secreted from the Paneth cell granules. The mature HD5 (aa 63-94) is protected from further digestion by the proteolysis enzyme. HD5 functions in maintaining the correct microbial balance in the intestine. Transgenic mice that express HD5 are protected from lethal challenge caused by Salmonella typhimurium. Expression levels of HD5 are negatively correlated to intestinal infection. HD5 is a useful marker for intestinal metaplasia of the upper gastrointestinal tract. HD5 expression has also been detected in the upper half of the stratified squamous epithelium of the vagina and ectocervix with increasing intensity toward the lumen. Secreted HD5 is detectable in cervicovaginal lavages, with highest concentrations during the secretory phase of the menstrual cycle.The monoclonal antibody 8C8 was raised against recombinant HD5 (aa 20-94) and recognizes the propeptide and the partially processed forms (aa 36-94 and 56-94), but it hardly recognizes mature peptide. No cross reactivity with HD6, lysozyme, or sPLA2 could be detected.