Heterophile antibodies arise when people are exposed to different animals or products derived from animals. These antibodies are typically human anti-mouse (HAMA), anti-rabbit, anti-goat, anti-sheep, anti-cow, anti-pig, anti-rat or anti-horse. As far as immunodiagnostics is concerned, the problem is most commonly associated with HAMA due to the fact that most diagnostics assays use mouse derived antibodies (1).
Two antibodies offered by Advanced ImmunoChemical, Inc. have been converted to chimeric proteins by changing the antibody constant regions from mouse to human derived sequences. The chimeric cTnI antibodies Rec19C7 and Rec16A11 consist of the original mouse derived variable regions that are responsible for antigen specificity and human derived constant regions of IgG1 isotype (see Figure 1).
Figure 1. Schematic illustration of HyTest chimeric cTnI antibodies.
In diagnostic tests, HAMA might cause false positive results that can cause delays in making a correct diagnosis in AMI (2-3). A study of subjects investigated with cardiac Troponin I due to suspected muocardial infarction found that HAMA caused false positivws in 5.5% of subjects raised with cTnI and 14% of subjects with raised cTnI and normal creatine kinase (4).
A powerful tool to solve the issue with HAMA in diagnostic tests is the use of chimeric or fully humanized antibodies. Troponin assays are particularly susceptible to HAMA due to low cut-off value requirements and becuase the levels of cTnI even in the plasma of AMI patients are very low.
Figure 2. Human anti-mouse antibodies (HAMA) can cause both false positive and false negative results in immunoassays.
Isotype switch has no effect on performance chimeric cTnI antibodies. See AssayNotes.
Chimeric antibodies mitigate the HAMA effect in In vitro diagnostic assays. See AssayNotes.
- Rahman, A. and Broadley, S.A. Review article: Elevated troponin: diagnostic gold or fool’s gold? Emerg. Med. Australas., 2014, 26, 125-130.
- Morton, A. When lab tests lie….heterophile antibodies. Aust. Fam. Physician 2014, 43, 391-393.
- Zaidi, A. and Cowell, Rl. False positive cardiac troponin elevation due to heterophile antibodies – more common than we recognize. BMJ Case Reports, 2010, bcr1120092477.
- Fleming, S.M. et al. False positive cardiac troponin I in a routine clinical population. Am. J. Cardiol. 2002, 89, 1212-1225.