Molecular and immunological characterization of Mycobacterium avium 65 kDa heat shock protein (Hsp65).

The heat shock protein Hsp65 has been characterized previously in several mycobacterial species. This is the first report of the complete sequence of the coding region of the Mycobacterium avium homologue. The sequence was highly homologous to the Hsp65 of other mycobacterial species, as well as being related closely to the murine and human homologues. Recombinant Hsp65 (rHsp65) was expressed in Escherichia coli to high levels and the recombinant protein tested for its immunogenicity in a murine model of M. avium infection. Although mice infected with M. avium produced antibodies that reacted with rHsp65, they showed low proliferative T-cell responses and no cytokine production in response to the same antigen. However, immunization with rHsp65 in the adjuvant dimethydioctadecylammonium bromide (DDA), induced T cells that responded to native Hsp65 with proliferation and IFN-gamma production, indicating that the recombinant and native forms of the protein were antigenically similar. Therefore, the findings indicate that Hsp65 is not a dominant T-cell antigen during M. avium infection.