Detection of human hepatitis anti-liver kidney microsomes (LKM2) autoantibodies on rat liver sections is predominantly due to reactivity with rat liver P-450 IIC11.

Anti-liver kidney microsomes (anti-LKM2) autoantibodies, appearing in patients treated with tienilic acid and suffering from hepatitis, react with proteins in rat liver sections. The nature of the rat proteins responsible for this recognition and detection of anti-LKM2 has been investigated. Immunoblot testing of the anti-LKM2 with liver microsomes from diversely treated rats and with purified rat liver cytochromes P450 (IA1, IA2, IIB1, IIB2, IIC6, IIC11 and IVA1) showed that these antibodies cross-reacted with cytochrome P450IIC11 and also with phenobarbital-induced cytochromes P450IIB1 and IIB2. Moreover, metabolic activation of tienilic acid and of a tienilic acid isomer by untreated rat liver microsomes was partially inhibited by anti-LKM2. On the other hand, monospecific polyclonal anti-rat P450IIC11 antibodies cross-reacted with human microsomal cytochromes P450 and recognized the same cytochromes P450 as anti-LKM2. This antibody also gave an immunofluorescence pattern on rat and mouse liver and kidney sections very similar to anti-LKM2. The data presented here show that anti-LKM2 recognize epitopes shared by rat P450 IIC11, and a human P450 of the family IIC. All the results indicate rat P450 IIC11, the major isoenzyme present in normal adult male rat liver, as the main antigen recognized by human anti-LKM2 autoantibodies; this is the basis of the immunofluorescence test for detection of these antibodies.