Identification of immunoreactive regions of rubella virus E1 and E2 envelope proteins by using synthetic peptides.

Relatively large (16-33 aa) synthetic peptides (SPs) representing defined sequences of rubella virus (RV) E1 and E2 envelope proteins were used in lymphocyte stimulation and enzyme immunoassays to map immunoreactive regions recognized by peripheral blood mononuclear cells (PBMNC) and serum antibodies from healthy RV-seropositive, RV-seronegative, and RV-vaccinated adults. Five distinct immunoreactive regions were identified in RV E1 protein, spanning residues (11-39), (154-179), (199-239), (226-277), and (389-412), which stimulated cellular responses in 29-83% of the subjects tested. Two SPs, E1(213-239) and E1(258-277) containing previously-identified virus neutralizing antibody domains, reacted with serum antibodies and also stimulated lymphoproliferation suggesting that these E1 sequences contain linked or overlapping B-and T-cell antigenic sites. The frequency and magnitude of cellular responses to E2 SPs were somewhat lower. SPs encompassing E2 residues (50-72), (140-199), and (244-263) stimulated lymphocyte responses in 28-64% of the subjects tested, while to a lesser degree, SPs within residues (1-36) were also stimulatory. E2 SPs within the regions (1-36), (151-170), and (244-263) also showed low levels of antibody reactivity with sera from RV-seropositive subjects. E2(244-263) which induced the highest level of response among the E2 SPs tested, was of interest due to previous reports of sequence homology of this RV region with human myelin and its potential immunopathogenic role in demyelinating autoimmune diseases. Identification of these potentially immunodominant regions of RV envelope proteins is an important first step in the rational design of new RV vaccines.