Borrelia burgdorferi outer surface protein A (OspA) (OspA)

Borrelia burgdorferi outer surface protein A (OspA) is a major surface-exposed lipoprotein of the spirochete that causes Lyme disease (UniProt: P0CL66). It is predominantly expressed when the bacteria are in the midgut of the Ixodes tick vector, where it mediates attachment to the tick gut protein TROSPA (PubMed: 15210926). Related antigens such as OspB and OspC also play roles in the bacterial life cycle, with OspC being essential for mammalian infection (PubMed: 15731211). During the tick's blood meal, OspA is downregulated as the bacteria migrate to the salivary glands and upregulate OspC for transmission to the mammalian host (PubMed: 10376650). Because OspA is present in the tick but largely absent in the host during early infection, it serves as a unique target for transmission-blocking vaccines. These vaccines work by inducing antibodies in the human host that are ingested by the tick during a blood meal, neutralizing the bacteria before they can be transmitted (CDC: Lyme Disease Vaccine). While the first human OspA vaccine, LYMErix, was withdrawn due to concerns over potential autoimmune cross-reactivity, newer multivalent candidates like VLA15 are designed to protect against multiple Borrelia species and strains by targeting various OspA serotypes (ClinicalTrials.gov: NCT04050917).

Other names

Outer surface protein AOspABBA15Borrelial lipoprotein OspAOuter surface protein B (OspB)Outer surface protein C (OspC)VlsE

Induction of host antibodies that neutralize Borrelia burgdorferi within the tick midgut during a blood meal, preventing transmission to the mammalian host.