**7. Hsps in vaccine development against TB**

Hsps are among the proteins that are expressed at high level during the TB infection and are highly conserved. They could mediate the T cell sensitization required for the production of antibodies and can be used in the development of vaccine(s) against TB (Lussow et al., 1991). Inside the host, T cells are involved in activating macrophages and controlling the mycobacterial infection. Both the macrophage and mycobacterium synthesize heat shock proteins in order to facilitate their survival, and these Hsps possess potent immunogenicity (Munk & Kaufmann, 1991). The Hsp70 of *M. tuberculosis* has been shown to have antiinflammatory properties and immunosuppressive role in a graft rejection system (Borges et al 2010). Hsp70 is recognized by human CD4+ T-cells and it leads to the secretion of TNF, IL-6 and IL-1β (Asea et al., 2000). Mycobacterial Hsp70 can be used in subunit vaccine design since it contains a variety of T-cell epitopes (Oftung et al., 1994). Studies have been done to map the epitopes of Hsp70, so as to eliminate the autoimmune response in humans (Adams et al., 1993). A synthetic peptide, non-covalently bound to *M. tuberculosis* Hsp70 generated a very strong specific proliferative T-cell response in the spleen of mice (Roman & Moreno, 1996).

Hsp16 also induces T-cells to proliferate and secret cytokines, and therefore can be used as a potential subunit vaccine candidate (Agrewala & Wilkinson, 1999). A DNA vaccine combination expressing mycobacterial Hsp65 and IL-12 provided high degree of protection against TB (Okada et al., 2007). The vaccine was delivered by the hemagglutinating virus of Japan (HVJ)-envelope and liposome. This vaccine provided remarkable protection in mice and monkeys compared to the BCG vaccine, demonstrating the potential of Hsps to be used in vaccine development (Okada, 2006; Okada & Kita; Okada et al., 2007; Okada et al., 2009). A prime-boost strategy was investigated in cattle, using a combination of three DNA vaccines coding for Hsp65, Hsp70, and another mycobacterial protein Apa for priming, followed by a boost with BCG prior to experimental challenge with virulent *M. bovis* (Skinner et al., 2003).

Hsp65 as an antigen can confer protection equal to that from live BCG vaccine (Silva, 1999). The mycobacterial Hsp65 and Hsp70 acted as carrier molecules in mice previously primed with *M. tuberculosis* and showed high and long-lasting titers of IgG (Barrios et al., 1992; Perraut et al., 1993). The mycobacterial Hsp65 conjugated to peptides or oligosaccharides in the absence of adjuvants, induced antibodies which cross-reacted well with Hsp homologues from other prokaryotes, but weakly with the human Hsp homologue (Barrios et al., 1994). The PBMCs and T-cell lines from *M. leprae* and *M. bovis* BCG vaccinated subjects showed proliferation in response to Hsp18 and Hsp65 of *M. leprae*, Hsp65 of *M. bovis* BCG, and the Hsp70 of *M. tuberculosis* (Mustafa et al., 1993). The response of T cells to these Hsps makes them eligible for their application in the next generation of subunit vaccines (Mustafa et al., 1993).

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