Mapping of B cell epitopes in measles virus nucleocapsid protein

The B-cell response against measles nucleoprotein (MeN) plays an important role in the control of measles infection. However, the data on B cell epitopes of MeN are still limited. The objective of this study was to identify B cell epitopes in MeN using monoclonal and polyclonal antibodies raised against recombinant yeast-expressed MeN (rMeN) as well as human sera from measles-positive individuals. After immunization of mice, 15 monoclonal antibodies (mAbs) against rMeN were generated. The B cell epitopes were localized using recombinant overlapping MeN fragments, PepScan analysis, and competitive ELISA. The epitopes of 14 mAbs were mapped within the C-terminus of MeN between amino acids (aa) 419 and 525. Four mAbs recognized a linear epitope located within a sequence of aa 440-448. Competitive ELISA revealed a cluster of conformational mAb epitopes. Cross-inhibition studies with human sera demonstrated similar localization of B cell epitopes recognized by serum antibodies from naturally infected individuals. Thus, the majority of B cell epitopes are located at the C-terminal domain of MeN. These findings provide new data on the antigenic structure of MeN and are in agreement with recent experimental evidence indicating that the C-terminal domain of MeN is well accessible on the surface of nucleocapsid-like structures.