Heat shock proteins as carrier molecules: in vivo helper effect mediated by Escherichia coli GroEL and DnaK proteins requires cross-linking with antigen.

In the past few years we have shown that mycobacterial heat shock proteins (hsp) of 65 and 70 kD exert a very strong helper effect in mice and monkeys when conjugated to peptides and oligosaccharides and given in the absence of adjuvants. In the present study we show that this adjuvant-free helper effect (i) is not due to lipopolysaccharide (LPS), since it was observed in LPS-resistant mice (C3H/HeJ) immunized with hsp-based constructs containing the malaria peptide (NANP)40, and (ii) is characteristic of hsp, since it was not observed with conjugates containing the mycobacterial p38 antigen, which is not a stress protein. Interestingly, the hsp GroEL and DnaK of Escherichia coli, which share a high degree of homology with the mycobacterial 65-kD and 70-kD hsp, respectively, exhibit a strong in vivo helper effect when conjugated to the (NANP)40 peptide, and the conjugates given in the absence of adjuvants. This in vivo helper behaviour of the GroEL and DnaK proteins corresponds well to that observed with the mycobacterial 65-kD and 70-kD hsp, respectively, since the hsp65- and GroEL-based constructs require previous priming of the animals with live bacille Calmette-Guérin (BCG), which is not needed for the hsp70- and DnaK-based constructs. Finally, using both mycobacterial and E. coli hsp we show that their in vivo helper effect in the absence of adjuvants requires cross-linking to the synthetic peptide. Taken together, our results suggest that the adjuvant-free helper effect observed with mycobacterial and E. coli hsp may be a generalized phenomenon, exhibited by hsp from diverse microorganisms. These findings may find applications in the design of vaccine constructs.