Outer surface protein A (OspA) (OspA)

Outer surface protein A (OspA) is a 31-kDa lipoprotein anchored to the outer membrane of Borrelia burgdorferi, the primary causative agent of Lyme disease [1]. It is predominantly expressed while the spirochete resides in the midgut of its tick vector, Ixodes scapularis, where it mediates bacterial attachment to the tick midgut receptor TROSPA [2]. This attachment is essential for the colonization and persistence of the bacteria within the tick during its dormant periods between blood meals [2]. Upon the initiation of a blood meal, OspA is downregulated as the bacteria migrate to the tick's salivary glands for transmission to a mammalian host, a process typically requiring 36 to 48 hours of attachment [3]. Because OspA is not expressed in the human host, it serves as a unique "transmission-blocking" vaccine target; antibodies generated by the host are ingested by the tick and neutralize the bacteria before they can exit the midgut [4]. The first OspA-based vaccine, LYMErix, was approved by the FDA in 1998 but later withdrawn due to commercial factors and theoretical concerns regarding molecular mimicry with human LFA-1 [3, 5]. Currently, OspA remains the focal point for second-generation multivalent vaccines, such as VLA15, which target multiple serotypes to provide broader geographic protection [5].

Other names

OspABBA15Outer surface lipoprotein ABorrelia burgdorferi surface antigen

Induction of host-derived bactericidal antibodies that neutralize Borrelia burgdorferi within the tick midgut during a blood meal, thereby preventing transmission to the host [3, 4].