Rabbit-derived anti-HD antibodies for HDAg immunoblotting

We studied the sensitivity and specificity of two rabbit-derived antibodies (W2 and W3) raised against two synthetic peptides of the HDAg: the C-terminus of the p24 protein (W2) and the C-terminus of the p27 protein (W3) (Chiron Co., Emeryville, CA, U.S.A.). The results were compared with those obtained with a human polyclonal anti-HD (W1). We have tested W2 and W3 against blotted serum samples from 25 patients (20 HBsAg positive anti-HD positive, three HBsAg positive anti-HD negative and two HBsAg negative anti-HD negative) and liver extracts from five HBsAg seropositive patients, two anti-HD positive and three anti-HD negative. In serum samples W3 sporadically reacted with a p31 protein present in both anti-HD positive and negative sera; W2 identified the p24 protein in 7/10 W1 positive samples but in none of 10 W1 negative; the p27 protein was captured by W2 only in one highly viremic serum. In every sample of liver extract W3 recognized a 48-kDa band. W1 and W2 stained 5 bands at 45, 27, 24, 16 and 12 kDa. The p45, p27 and p24 proteins were peculiar of HDV-infected livers; p16 and p12 were also detected in HDV free livers. W2 identified an additional 54-kDa protein in 4/5 liver extracts. For diagnostic purposes human polyclonal anti-HD represents the most sensitive probe for HDAg immunoblotting, with a specificity similar to that of rabbit-derived antibodies. The affinity of W2 and W3 antibodies for serum and liver HDAg appears to be lower than for HDAg recombinant.(ABSTRACT TRUNCATED AT 250 WORDS)