Immunological analysis of the protective responses to the chimeric synthetic peptide representing T- and B-cell epitopes from the fusion protein of measles virus

The role of different adjuvant formulations and routes of immunization on the antibody responses and protection induced in mice was determined by a synthetic peptide representing T- and B- cell epitopes from the measles virus (MV) fusion (F) protein (TTB peptide) which has previously been shown to induce protective responses against MV encephalitis in mice. When the peptide TTB was administered in Freud's complete adjuvant (FCA), Freud's imcomplete adjuvant (FIA), alum or with IL-2, anti-peptide antibody responses and anti-MV antibody responses were detected. Interestingly, immunization with TTB without adjuvant resulted in the induction of anti-peptide antibody responses which did not cross react with the MV. The use of FIA as an adjuvant led to a significantly higher IgG2a antibody response compared with FCA and alum, whereas alum led to a significantly lower IgG3 response. Immunization with TTB in FCA, FIA and alum led to the generation of high affinity antibodies (with alum generating the highest affinity), whereas immunization of peptide with IL-2 or in PBS resulted in the induction of antibodies of lower affinity. Only the FCA, FIA and alum formulations led to the induction of protective responses in mice against MV-induced encephalitis. When the subcutaneous route (s.c.) of immunization was compared with the intraperitoneal route (i.p.), s.c. immunization with the TTB peptide led to higher anti-peptide and anti-MV antibody responses and higher affinity antibodies compared to those induced following i.p. immunization. Mice receiving the TTB peptide via the s.c. route had a higher percentage survival after MV challenge than those immunized via the i.p. route. These results show that the nature of the adjuvant used as well as the route of immunization play an important role in the induction of protective anti-TTB peptide antibody responses against MV-induced encephalitis in mice.