Cellular and humoral immune responses to vaccines of hepatitis B type and rabies were inhibited by specific inhibitors of cathepsin B, specific synthetic substrates of cathepsin B and anti-cathepsin B antibody. Therefore the lysosomal cathepsin B of antigen presenting cells plays an essential role in processing of these antigens for presentation to MHC class II. One of the active sites of cathepsin B, VN217–222 shares highly homologous sequences with a part of the desetope, a binding domain of antigenic peptides, VN57–62 of MHC class II, β-chain. This evidence suggests that the peptides processed by the substrate specificity of cathepsin B exhibit a common affinity to bind with the desetope of MHC class II, β-chain.
