Specificity of the newly established MoAbs HSL11, HSL96, and HSL2 for human λ5, VpreB, and pre-BCR, respectively. A pre–B-cell line NALM6 (A), a pro–B-cell line RS4;11 (B), and X63.Ag8-653 cells transfected with either the λ5 or VpreB gene (C) were biosynthetically labeled with [³⁵S]-methionine for 4 hours and lysed with 1% NP-40 lysis buffer. Detergent-soluble lysates were incubated with indicated MoAbs, and immunoprecipitates were analyzed by 13% SDS polyacrylamide gel electrophoresis under reducing conditions. The positions of μH, λ5, and VpreB are indicated by arrows, and a 16-kD band precipitated by HSL11 together with λ5 is indicated by an arrow head.