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Identifying and analyzing biological mixture samples at a crime scene are of paramount concern for forensic scientists, especially if that type of evidence contains only one cell type. The presence of multiple contributors in a biological evidence sample reduces the probative value of DNA evidence and can sometimes lead to its eventual loss of value. As such, this study was performed in an attempt to examine and evaluate flow cytometry analysis as a means to separate blood mixture samples labeled with fluorescent antibodies. Fluorescein Isothiocyanate (FITC) antibodies were specifically targeted and bound to HLA (Human Leukocyte Antigens) markers present on nucleated cells in the blood, after which they were isolated from the blood mixture utilizing Fluorescent Activated Cell Sorting (FACS) - A high throughput technique that separates cell populations based on their optical activity, followed by STR analysis. This approach was tested on fresh blood mixtures containing two contributors, where one contributor possessed an HLA A*02 allele that was not shared with the other contributor. We hypothesize that HLA A*02 positive samples would exhibit fluorescence when bound with the fluorescently labeled antibodies while the HLA A*02 samples would not. As such, we would be able to separate both cell populations using FACS followed by STR analysis. Such a work flow is believed to yield discriminant STR profiles unique to each contributor thus increasing the probative value of the evidence at hand. Results supported our hypothesis and yielded discriminant STR profiles for both contributors, with minor peaks from the A*02 negative contributor being observed in A*02 positive contributor sample. We can then conclude that HLA-A*02 antibodies coupled to FACS is a suitable method that can be utilized to evaluate and separate blood mixture samples in an attempt to yield discriminant STR profiles.
Forensic Science, Cellular Immunochemistry
FACS, Flow Cytometry Analysis, HLA A*02, Antibody Hybridization, Blood Analysis, FITC labeled, STR Profiling
Biochemistry | Molecular Biology
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