Evaluation of PE_PGRS33 as a potential surface target for humoral responses against Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) PE_PGRS33 is a surface-exposed protein that was shown to interact with Toll-like receptor 2 on host macrophages to induce inflammatory signals and promote entry in macrophages. In this study, we investigated PE_PGRS33 as a potential target of a humoral response aimed at hampering key processes in tuberculosis pathogenesis. PE_PGRS33 protein was successfully expressed and purified under native condition in Escherichia coli. The purified protein retained its native functional and biological properties, showing the ability to elicit proinflammatory signals in murine and human macrophages. Interestingly, a polyclonal antiserum raised against native PE_PGRS33 showed no cross-reactions with other mycobacterial proteins. The anti-PE_PGRS33 serum was also able to inhibit Mtb entry into macrophages, but it did not reduce entry of the Mtb Delta pe_pgrs33 strain. Addition of native recombinant PE_PGRS33 to the Mtb Delta pe_pgrs33 strain during infection restored the Mtb wild-type entry phenotype in macrophage. Moreover, the anti-PE_PGRS33 serum was able to neutralize the proinflammatory activity of PE_PGRS33 in vitro. Furthermore, mice immunized with native recombinant PE_PGRS33, but not with a DNA vaccine expressing PE_PGRS33, were able to restrict M. smegmatis in vivo. These results highlight the potential use of PE_PGRS33 as a target of a neutralizing humoral response against tuberculosis.