HSPD1 and rheumatoid arthritis: However, unlike inbred rats, which are genetically homogeneous and generate immune response mainly to heat-shock protein 65 (Hsp65) during the course of AA [22], RA patients have diverse genetic make-ups and generate immune response to different target antigens, including Hsp65 and collagen type II (CII) [3,23,24,25,26].