Iron acquisition systems in the pathogenic Neisseria

Pathogenic neisseriae have a repertoire of high-affinity iron uptake system s to facilitate acquisition of this essential element in the human host, Th ey possess surface receptor proteins that directly bind the extracellular h ost iron-binding proteins transferrin and lactoferrin. Alternatively, they have siderophore receptors capable of scavenging iron when exogenous sidero phores are present. Released intracellular haem iron present in the form of haemoglobin, haemoglobin-haptoglobin or free haem can be used directly as a source of iron for growth through direct binding by specific surface rece ptors. Although these receptors may vary in complexity and composition, the key protein involved in the transport of iron (as iron, haem or iron-sider ophore) across the outer membrane is a Tons-dependent receptor with an over all structure presumably similar to that determined recently for Escherichi a coli FhuA or FepA. The receptors are potentially ideal vaccine targets in view of their critical role in survival in the host. Preliminary pilot stu dies indicate that transferrin receptor-based vaccines may be protective in humans.