Detection of dermcidin for sweat identification by real-time RT-PCR and ELISA.

We evaluated the performance of real-time RT-PCR and ELISA assays for detection of dermcidin (DCD) in sweat and body-fluid stains. DCD, a small antibiotic peptide secreted into human sweat, was detected by real-time RT-PCR in 7-day-old stains containing as small as 10μL of sweat, and the assay showed high specificity when testing 7-day-old stains containing 30μL of other body-fluid. ELISA using anti-human dermcidin mouse monoclonal antibody detected DCD sweat diluted up to approximately 10,000-fold and could specifically detect DCD in 10μL of body-fluid stains. The performance of the two assays was tested during winter on samples that simulated forensic case samples: an undershirt and a sock worn for 20h, a handkerchief used to wipe the brow several times within 12h, a cap and a cotton glove worn for 4h, and a white robe worn at intervals for 2 years. The result showed that the former assay detected DCD in all sites of the undershirt examined (armpit, back, and breast), and the latter gave a relatively high OD value in the armpit among the three sites. For the socks, although the latter assay gave very high OD values in both the center and toe of the foot sole, the former could not detect DCD in both of them. These results indicate that highly damp conditions, such as inside a shoe, might promote the degradation of mRNA in samples such as socks. In the other case samples, sweat was adequately detected by both assays.