56-kDa type-specific antigen (Orientia tsutsugamushi) (TSA56)

The 56-kDa type-specific antigen (TSA56) is the most prominent and immunodominant surface protein of Orientia tsutsugamushi, the causative agent of scrub typhus (UniProt P23925). It is an outer membrane protein that constitutes approximately 10-15% of the total bacterial protein content and acts as a major adhesin, mediating bacterial attachment and entry into host target cells like endothelial cells (PMID: 30103517). Because it is the primary target for neutralizing antibodies, TSA56 is the central focus for serological diagnosis and recombinant vaccine development (PMID: 32664500). A significant challenge in targeting this molecule is its high degree of sequence variability, which results in multiple distinct serotypes such as Karp, Kato, and Gilliam (StatPearls, Scrub Typhus). While clinical management currently relies on antibiotics like doxycycline that target the bacterial ribosome, TSA56 remains the primary target for immunological interventions aimed at blocking the initial infection phase.

Other names

Major surface protein56 kDa proteinp56Type-specific antigen 56OmpA-like protein

Neutralization of bacterial attachment and entry into host cells by antibodies.