The relative abundance of two measles virus fusion protein peptide-DR1 complexes expressed by B cells is independent of the form of the antigen.

The relative processing and presentation efficiency of two DR1-restricted determinants from the fusion protein (F protein) of measles virus (MV) was determined using three forms of antigen (Ag): MV, an F protein recombinant vaccinia virus, and a chimerical polypeptide between the glutathione S-transferase and the F protein (GST-F protein). First, it was shown that these different preparations of F protein have distinct processing requirements. In MV-infected B cells, the F254 determinant (contained within the F protein sequence 254-268) relies on protein synthesis for its presentation, while the F314 determinant (contained within the F protein sequence 314-328) is also presented in the absence of protein synthesis. By contrast, in GST-F protein-pulsed B cells, presentation of both determinants is dependent on protein synthesis. Then, it was established that, independently of the form of the Ag, the F314 determinant was considerably more (18- to 36-fold) efficiently processed and presented than the F254 determinant. These results indicate that determinants from the same protein are displayed by antigen-presenting cells at widely different levels and they may also suggest that this is an intrinsic characteristic of the determinants, rather than a feature controlled by the processing pathways followed by the Ag