Characterization of humoral immune response against the immunoglobulin-binding protein (BIP) of Giardia lamblia: A potential vaccine candidate.

Giardiasis is caused by the widespread intestinal parasite Giardia lamblia. The characterization of immunogenic proteins in G. lamblia has been investigated to identify potential vaccine targets, including members of the giardin family, variant-specific surface proteins (VSPs), cyst wall proteins (CWPs) and heat shock protein (HSP). The immunoglobulin-binding protein (BIP) is a HSP that has been described as immunogenic antigen; however, its role in this protozoan remains poorly characterized, particularly regarding its involvement in the humoral immune response activation, critical for parasite clearance. In this study, we evaluated the capacity of BIP to promote an antibody-mediated response through oral administration in mice. Additionally, we identified B-cell epitopes by integrated experimental and immunoinformatic approach. In mice, oral administration of BIP alone, without adjuvants, induced a specific humoral immune response at both systemic and mucosal levels, as well as, during Giardia infection, demonstrating its ability to disrupt the tolerogenic environment of the gut. Immunogenic regions of BIP were identified. A fragment around 7 kDa was recognized by specific-BIP polyclonal and monoclonal antibodies. This fragment contains two potential linear epitopes (the amino acids 64-132 and 176-190 of BIP protein) that are conserved in HSPs of other pathogens. Furthermore, in silico analyses identified additional B-cell epitopes distributed throughout the BIP sequence, reinforcing its antigenic potential. These findings support the ability of BIP to induce an efficient humoral immune response via the oral route, a key feature in infections such as giardiasis, thereby highlighting its potential as a target for vaccine development against Giardia.