“…In addition, in SNP-pretreated groups, rats that did develop AA were found to have lower clinical as well as radiographical scores compared with rats ofthe FIA-pretreated control groups (Tables 1 and 2). Interestingly, SOP, an A'-acetylated octapeptide lacking the N-terminal threonine of 11,14,17,19,19,21,23 SNP, did not have any protective capacity (experiment 2, Tables 1 and 2), AA incidence and severity in SOP-pretreated rats were not difTerent from FtA-pretreated controls (Tables t and 2), This points to the specificity of the SNP effect in AA, It has been postulated that suppression of autoimmune disease in animals is usually caused by the induction of tolerance to the autoimmune disease-inducing antigen (Higgins & Weiner, 1988;Thomson et al, 1988;Clayton et al, 1989), i,e, the protection against mycobacteria-induced arthritis after pretreatment with whole mycobacteria or the 65-kD HSP, is due to induction of tolerance (Grey & Waksman, 1967;Cozine et al, 1972;van den Broek et al, 1989), This led us to investigate the cellular immune response of the rats to SNP, SOP and M. tuberculosis in vivo and in vitro after 35 days of pretreatment but before induction of AA and also 35 days after induction of AA, Before induction of AA, SNP-pretreated rats showed a DTH to SNP, but not to M. tuberculosis (Table 3), Normal rats and FIA-pretreated rats did not show a DTH to SNP, An in vitro proliferative response of splenic MNC to both SNP and M. tuberculosis is found in SNP-pretreated rats, but not in normal or FtA-pretreated rats (Table 3), Interestingly, no crossreactivities between SOP and SNP or M. tuberculosis were observed (Table 3), This is consistent with the fact that T cell clones A2b and A2c do not recognize the epitope without the N-terminal threonine (van der , Therefore it can be concluded that the threonine at position of 180 ofthe 65-kD mycobacterial HSP is important for immunogenicity of the nonapeptide.…”