Mycobacterium tuberculosis HBHA Protein Reacts Strongly with the Serum Immunoglobulin M of Tuberculosis Patients

Abstract

Identification and characterization of serologically active mycobacterial antigens are prerequisites for the development of diagnostic reagents. We examined the humoral immune responses of active tuberculosis (TB) patients against Triton-soluble proteins extracted from Mycobacterium tuberculosis by immunoblotting. A 29-kDa protein reacted with immunoglobulin M (IgM) in the pooled sera of the patients, and its N-terminal amino acid sequence matched that of the heparin-binding hemagglutinin (HBHA). Recombinant full-length HBHA was expressed in Escherichia coli (rEC-HBHA) and M. smegmatis (rMS-HBHA). In immunoblot analysis, the IgM antibodies of the TB patients reacted strongly with rMS-HBHA but not with rEC-HBHA, whereas the IgG antibodies of these patients reacted weakly with both recombinant HBHA proteins. In enzyme-linked immunosorbent assay analysis using rMS-HBHA and 85B as antigens, the mean levels and sensitivities of the anti-HBHA IgM antibodies of the TB patients were significantly higher than those of the anti-antigen 85B IgM antibodies, while the IgG antibodies showed the opposite results. Of interest in this respect, the pooled sera from the TB patients that contained anti-HBHA IgM antibodies neutralized the entry of M. tuberculosis into epithelial cells. These findings suggest that IgM antibody to HBHA may play a role in protection against extrapulmonary dissemination.

Antibodies and tuberculosis

“…Pre-coating of BCG with anti-HBHA mAbs prior to intranasal inoculation did not influence bacterial CFU in lungs, but led to a marked reduction in spleen colonization [101]. This finding supports previously described studies suggesting that antibodies directed against LAM prevented dissemination of infection and that anti-HBHA IgM is able to prevent epithelial cell invasion [92], [102]. However Parra et al.…”

“…Thus entry of mycobacteria into host cells may be prevented by the action of antibody. Humans produce high titres of IgM against mycobacterial heparin-binding hemagglutinin (HBHA), a surface expressed molecule that facilitates host cell invasion [92], [93]. Sera from such patients were able to prevent the entry of M.tb into an alveolar epithelial cell line [92].…”

Exploiting the mycobacterial cell wall to design improved vaccines against tuberculosis

“…These results imply that during M. tuberculosis infection the host-specific immune response directed against HBHA differs depending on the clinical status. These findings are relevant from a diagnostic point of view, since it would be possible to discriminate patients with active TB from those infected but with no overt sign of the disease [56][57][58][59][60][61]. At the same time, these differential immune responses in TB patients versus healthy TBinfected subjects may suggest that an effective T cell response against HBHA could help to control M. tuberculosis replication and prevent disease development [54,62].…”

Mycobacterium tuberculosis Rv1419 encodes a secreted 13 kDa lectin with immunological reactivity during human tuberculosis

“…Moreover, the existence of at least 11 hypothetical lectins from Mtb [21] suggests that these molecules may be an important component of the host-mycobacteria interplay. Consistent with this, active TB (ATB) patients have been found to display increased levels of anti-HBHA Ab during active disease [22,23], suggesting that mycobacterial lectins may elicit specific immune responses.…”