isohemagglutinin

https://doi.org/10.1351/goldbook.13346
Naturally occurring immunoglobulin M (IgM) antibody specific for the erythrocyte antigens of the ABO blood groups, thought to result from immunization by bacteria in the gastrointestinal and respiratory tracts.
Source:
PAC, 2012, 84, 1113. (IUPAC glossary of terms used in immunotoxicology (IUPAC Recommendations 2012)) on page 1196 [Terms] [Paper]