An enzyme-linked immunosorbent assay with monoclonal antibodies for the determination of phosphorylated hepatitis B core protein (p21c) in serum.

An enzyme-linked immunosorbent assay (ELISA) was developed for the determination of hepatitis B virus (HBV) core protein (p21c) using monoclonal antibody (mAb) directed to a phosphorylated C-terminal amino acid sequence that is not present in hepatitis B e antigen (HBeAg). HBV virions in the test serum were precipitated with horse polyclonal antibody to hepatitis B surface antigen (HBsAg), dissolved with Tween 20 and NaOH, and then neutralized. HBV core protein (p21c), released from HBV cores by this procedure, was sandwiched between immobilized mAb C33 directed to amino acids (aa) 133-140 of the core protein, fixed on a solid support and labeled mAb T2212 that recognizes aa 165-175, only when they are phosphorylated. The method was applied for the detection of phosphorylated p21c in sera from symptom-free carriers and patients with chronic hepatitis. The results indicated a higher extent of phosphorylation in p21c of HBV cores from symptom-free carriers than hepatitis patients.