NCJ Number
78482
Journal
Journal of Forensic Sciences Volume: 23 Issue: 3 Dated: (July 1978) Pages: 570-576
Date Published
1978
Length
7 pages
Annotation
This report describes laboratory experiments designed to produce selective destruction of the cross-reactivity associated with the MN blood group system and applies the results of this work to the detection of MN antigens in bloodstains.
Abstract
The MN blood group system is potentially valuable in discriminating between individuals. The system is based on the M and N antigen sites which are found on the red cell surface. The frequency of the sites' occurrence among the population is estimated at 30 percent M, 20 percent N, and 50 percent MN. The techniques in dried blood are the same as those used for the ABO system: absorption-elution or inhibition. However, results of proficiency testing show that MN testing involves an error rate as high as 40 percent, compared to 1.6 percent for ABO testing. Two factors cause the problem in MN testing: the possibility of detecting N antigen on M cells and the commercial production of anti-N sera which are unsuited to bloodstain typing. The present experiments involved the use of the enzyme alpha-chymotrypsin (thrice crystallized) to destroy the cross-reactivity. Techniques used in the experiments are explained in detail. Basically, results showed promise for the identification of the true M and N antigens in bloodstains. Findings demonstrate that serological results must be interpreted with caution, especially until all the serological, immunological, and biochemical facts are known. When there are obvious inconsistencies in results and when errors are being made during blood grouping, as there are in the MN system, a skeptical attitude should be maintained before using that system in practice. Tables and a list of 30 references are provided.