Identification of rectal mucosa-secreted proteins by enzyme-linked immunosorbent assay for the investigation of sexual assault cases with anal penetration.

To aid the criminal investigation of sexual assault with anal penetration, we developed the enzyme-linked immunosorbent assay (ELISA) to identify Chloride Channel Accessory 1 (CLCA1), a rectal mucosa-secreted protein, in samples collected from foreign objects at the crime scene or from the suspect’s body. The developed procedure was highly specific to samples swabbed from the rectal mucosa and might be sensitive enough to test a trace sample collected from the crime scene. In addition, most of the sexual assault–related contaminants tested in this study showed less influence on the ELISA detection of CLCA1. However, indirect ELISA is likely to be affected by an excessive amount of non-antigen proteins included in other body fluids. In contrast, the multiplex RT-PCR procedure for rectal mucosa markers we previously developed was less sensitive but resistant to the contamination of other forensically relevant body fluids in sexual assault cases. Therefore, both procedures should be selected appropriately or performed in combination, depending on the sample condition, to enable the precise determination of rectal mucosa markers.