Determination of ABO blood groups from saliva and saliva stains by an indirect enzyme-linked immunosorbent assay (ELISA) using monoclonal antibodies.

The detection of A, B and H blood group substances (ABH-BGS) in saliva and in saliva stains has been investigated quantitatively by an indirect ELISA using a horseradish peroxidase conjugate in combination with the use of monoclonal antibodies. Through this method, the reaction specificity to BGS in the saliva was very high and its detection sensitivity was found to be approximately 1,000 times greater than has been achieved in a hemagglutination-inhibition test. The monoclonal anti-A and anti-B reagents reacting with both secretor and non-secretor saliva in a hemagglutination-inhibition test and in this ELISA method were selected from among commercial monoclonal antibodies. However, no monoclonal anti-H reagent was found to react with non-secretor saliva. The BGS level was determined by the use of calibration curves of A, B and H standard BGS from human gastric mucosa and was expressed in units, based on the inhibition titer of the standard BGS. In 230 saliva samples, ABH-BGS were detectable, except for H BGS in non-secretor saliva. The BGS levels in saliva stains experimentally prepared were found to be approximately proportional to the levels in the original saliva. As for actual and aged stains, it was possible to detect BGS in most cigarette butts and in aged stains, however, such detection proved impossible in saliva samples from postage stamp.