Immunohistochemical staining of skin-expressed proteins to identify exfoliated epidermal cells for forensic purposes

The determination of cell type in biological casework samples would be helpful to identify the type of body fluids and interpret the DNA source in forensic laboratories. Exfoliated epidermal cells are considered to be a reasonable source of touch DNA; therefore, we developed and assessed an immunohistochemistry (IHC) procedure for identifying exfoliated epidermal cells as a screening test of touch DNA samples. Among five candidate protein markers investigated in this study, keratin 10 and kallikrein-related peptidase 5 were strongly expressed in the stratum corneum layer of the skin; however, their specificity was insufficient to identify epidermal cells. In contrast, IHC for corneodesmosin (CDSN), desmocollin 1 (DSC1), and filaggrin (FLG) was considered to be applicable because of their detectability and specificity on skin swab samples. Actually, CDSN and DSC1 could be good markers for exfoliated epidermal cells on touched contact traces that were contaminated with many unidentified impurities. Besides, positivity for FLG on mock casework samples appeared to be lower than for the other markers, which might be caused by its instability. Finally, the relationship between positivity for IHC and DNA yield was analyzed using skin swab samples. Although it was difficult to determine these correlations quantitatively because of the heterogeneous distribution of cells and the presence of cell-free DNA, the DNA-quantifiable samples analyzed in this study contained at least some of IHC-positive epidermal cells. In conclusion, IHC detection of skin-enriched proteins, especially CDSN and DSC1, could be useful for screening samples that have been handled or touched by someone before DNA analysis.