There are several antigenic variants in Rickettsia tsutsugamushi, and a type-specific antigen (TSA) of 56-kilodaltons located on the rickettsial surface is responsible for the variation [1,2]. TSA56 is found in Orientia tsutsugamushi (O. tsutsugamushi), the causative agent of scrub typhus, an obligate intracellular pathogen. TSA56 is one of the three major outer membrane proteins of O. tsutsugamushi. It is required for adhesion. Furthermore, it has been demonstrated that O. tsutsugamushi, can bind to fibronectin (Fn) via the antigenic membrane protein, TSA56. There are 3 extracellular antigen domains (ADs), where ADIII and adjacent C-terminal region of TSA56 waswere shown to be sufficient for Fn interaction and prohibiting Fn-enhanced invasion [3].

1: Purification and partial characterization of a type-specific antigen of Rickettsia tsutsugamushi. Ohashi N, Tamura A, Ohta M, Hayashi K; Infect Immun 1989;57:1427-1431. PMID:2496028

2: Diversity of immunodominant 56-kDa type-specific antigen (TSA) of Rickettsia tsutsugamushi. Sequence and comparative analyses of the genes encoding TSA homologues from four antigenic variants. Ohashi N, Nashimoto H, Ikeda H, Tamura A; J Biol Chem 1992;267:12728-12735. PMID:1618776

3: Molecular characterization of three major outer membrane proteins, TSA56, TSA47 and TSA22, in Orientia tsutsugamushi. Lin CC, Chou CH, Lin TC, Yang MC, Cho CL, Chang CH, Yu HS, Lai CH, Chen LK, Hong YR; Int J Mol Med. 2012;30:75-84. PMID:22505220