[Comparative study of various methods for the determination of the IgM or IgG class of antibodies, applied to the diagnosis of hepatitis A].

We report herein results of comparative study of different methods for determination of M or G classes of antibodies applied to serodiagnosis of type A hepatitis. We have examined retrospectively 259 sera with a technique employing protein A and 2 kits, HAVAB-M (RIA-M) and Hepanostika anti-HAV-IgM (ELISA-M). Some sera were studied after treatment by 2-mercapto-ethanol. We have obtained the same results with RIA-M and ELISA-M: 119 sera contain Ac anti-HAV of M class and 116 of G class, 24 sera non classified with protein A owing to their low level of Ac anti-HAV, are all but one of G class. We have observed 23 discrepancies between protein A or RIA-M and ELISA-M. A first group is constituted by 15 sera obtained during late convalescence and containing rates of Ac anti-HAV-M too low to be determined with protein A or 2-mercapto-ethanol so they are classified G, while RIA-M and ELISA-M, more sensitive, could detect such antibodies. Another group is constituted by 8 sera containing low rates of anti-HAV antibodies so we could not dilute them for reaction, and IgG were not adsorbed entirely on protein A while 2-mercapto-ethanol, RIA-M and ELISA-M led them being classified Ac anti-HAV-G. RIA-M and ELISA-M are useful tools particularly for sera obtained during late convalescence while protein A and 2-mercapto-ethanol are effective for diagnosis during 1 month after acute phase.