Determination of HCV protein specificity by recombinant immunoblot assay. For each patient (Pt), serum (S) and purified monoclonal Ig (Mc Ig) were incubated with blots carrying recombinant HCV nonstructural (NS) and core proteins. Serum and Mc Ig protein concentration was 4 μg/blot. Depending on the patient's Mc Ig, the horseradish peroxidase conjugates used were anti-γ, anti-α, or anti-μ chains. Typical results are shown for Mc Ig specific for HCV NS-4 protein (Pt 19) and Mc Ig specific for HCV core protein (Pt 21).