Study of antibody and T cell responses in rabbits immunized with synthetichuman B cell epitope analogues of La (SSB) autoantigen

The aim of this study was to investigate the immunogenicity of four synthet ic peptides, representing linear B cell epitopes of the human La/SSB autoan tigen: 145-164 aa (p1), 289-308 aa (p2), 301-318 aa (p3) and 349-364 aa (p4 ), in rabbits. New Zealand White rabbits were immunized with each of the ab ove peptides attached in four copies on tetrameric sequential oligopeptide carriers (SOC) in duplicate. Control immunizations were also performed (one rabbit each, immunized with Freud's complete adjuvant alone or with the SO C carrier alone). Animals were bled at regular intervals and sera were anal ysed for anti-La/SSB activity by ELISA assays using as antigen the various synthetic peptides, as well as the whole La/SSB protein. Four months after the last immunization, the animals were killed and peripheral blood mononuc lear and spleen cells were co-cultured with either the peptides, the SOC ca rrier, or 27 peptides, covering the entire length of the human La/SSB molec ule (23 amino acids long, overlapping by eight residues to each other). A s pecific, IgG, anti-peptide antibody response was detected, initially direct ed against the priming peptide, and subsequently expanded to the other La/S SB synthetic peptides. The antibody titres remained high, even 4 months aft er the last immunization. Sera from rabbits immunized with either p2 or p3 reacted also with the whole La/SSB protein, as was demonstrated by ELISA an d immunoblot assays. No reactivities against either Ro60 or Ro52 autoantige n were found. Rabbit spleen cell reacted not only with the epitope used for the immunization but also with other La/SSB peptides. Immunization of rabb its with the major human La/SSB B cell antigenic determinants, linked to SO C carrier, induces strong and sustained antibody and T cell responses again st multiple epitopes of the human La/SSB protein. Thus, La/SSB B cell linea r epitopes are probably capable also of functioning as T cell epitopes, in this experimental animal.