Chapter 18: Blood Group Typing and Protein Profiling

Blood groups represent inherited antigen variations present on the surface of red blood cells, with the ABO system standing as the earliest recognized classification system in this field. Understanding the molecular foundation of ABO genetics requires knowledge of distinct gene variants that encode specific glycosyltransferase enzymes, which determine the particular carbohydrate structures attached to the H antigen precursor molecule on cell surfaces, ultimately producing the recognizable A and B antigens. Forensic practitioners employ specialized laboratory techniques to identify these blood group markers in biological evidence, particularly the Lattes Crust method and the considerably more sensitive Absorption-Elution technique, both designed to detect antigens within dried bloodstains that may be years old. Beyond blood group analysis, protein profiling represents a complementary approach to forensic identification that focuses on naturally occurring variations in specific proteins circulating in serum and residing within blood cells. This technique harnesses electrophoretic separation methods that stratify proteins according to either their relative molecular mass or their isoelectric characteristics when placed in appropriate supporting media such as polyacrylamide or agarose matrices. The chapter details several key polymorphic proteins valuable for forensic casework, including Haptoglobin, which binds free hemoglobin; the vitamin D-binding Group-specific component; Transferrin, which transports iron throughout circulation; and Protease inhibitor, which regulates serum protease activity. Together, these analytical approaches provide forensic laboratories with independent lines of evidence for comparing biological samples recovered from crime scenes to reference standards, contributing to the broader framework of forensic serology as a discipline.