Abstract: A polypeptide having amino acid sequence 172-192 of a Mycobacterium bovis BCG 64 kD polypeptide, said sequence having the formula ##STR1## as well as polypeptides derived therefrom, in the amino acid sequence of which sequence 172-179 and/or sequence 189-192 is (are) entirely or partially absent, were found to be useful as immunogens inducing resistance to auto-immune arthritis and similar auto-immune diseases.The invention relates to these polypeptides, to polypeptides showing sequential homology with these polypeptides, and to derivatives and multimers thereof. Also, microorganisms expressing the polypeptides either as such or as part of a fusion protein or as a multimer form part of the invention.Finally, the invention relates to pharmaceutical compositions, diagnostic compositions and test kits comprising a compound according to the invention.