Lyme diseаse is the mоst cоmmоn vector-borne diseаse in the United Stаtes. It is caused by the Gram-negative spirochete Borrelia burgdorferi, which is transmitted through the bites of infected ticks. The ability of the bacteria to survive in the tick and in mammals depends on the differential expression or repression of particular genes. For example, the bacteria express an outer surface protein A (OspA) in the midgut of the ticks but downregulate OpsA in the mammalian host where temperatures are warmer. In humans the bacteria instead express another outer surface protein (OpsC). Both OpsA and OpsC have become primary targets for development of a vaccine against Lyme disease, and indeed, several commercial vaccines based on these extracellular proteins have been made and have been shown to have high efficacy in providing protective immunity in clinical trials. Question 1. Describe some reasons why OspA and OspC make good vaccine candidates.