No evidence of epitope spreading after immunization with the major Sm epitope P-P-G-M-R-P-P anchored to sequential oligopeptide carriers (SOCs)

The sequence Pro-Pro-Gly-Meth-Arg-Pro-Pro (PPGMRPP) is the major B-cell epi tope of the Sm autoantigen. The aim of the present study was to evaluate th e immune response against the native forms of Sm and U1RNP and immune media ted tissue injury after immunization with the sequence PPGMRPP anchored in five copies to a new type helicoid sequential oligopeptide carrier (SQC) fo rmed by the repetitive Lys-Aib-Gly moiety, [(PPGMRPP)(5)SOC5]. Rabbits (n = 3) were immunized with 0.5 mg of (PPGMRPP)(5)SOC5 in complete Freud's adju vant and boosted at days 26, 53, 99; control rabbits were immunized with th e PPGMRPP alone (n = 3), phosphate buffered saline (PBS) (n = 1), SOC, alon e (n = 1), a peptide at aminoacid (aa) position 158-177 of myelin basic pro tein (MBP aa 158-147) (n = 1) and three La/SSB autoantigen B-cell epitopes (n = 3). Antibodies to (PPGMRPP)(5)SOC5 were determined by enzyme linked im munosorbent assay (ELISA); precipitating anti-Sm and anti-U1RNP antibodies were detected by RNA precipitation and western blot on HeLa total cellular and nuclear extract and 12s sucrose gradient fraction of rat Liver extracts . High titres of anti-(PPGMRPP)(5)SOC5 antibodies not recognizing the nativ e forms of Sm or U1RNP antigens were detected in the (PPGMRPP)(5)SOC5 immun ized but not in the control animals. The sera of two (PPGMRPP)(5)SOC5 immun ized but not of the control rabbits recognized a 67 kDa protein in HeLa nuc lear extract, distinct from the 70 kDa U1RNP antigen. Diffuse and segmental increase of mesangeal matrix and cells, crescent formation, segmental glom erular necrosis, rarely massive subendothelial deposits occluding the lumen and C3 complement component in the mesangeal area were seen in the kidneys of one (PPGMRPP)(5)SOC5 immunized, but not of the remaining animals. In co nclusion, the immune response induced by (PPGMRPP)(5)SOC5 was specific for the immunizing epitope but not for the native forms of Sm and U1RNP antigen s, but it was associated with immune mediated kidney injury. (C) 2000 Acade mic Press.