The long strange trip of Borrelia burgdorferi outer‐surface protein C

Summary Borrelia burgdorferi must adapt physiologically to two markedly different host milieus and efficiently transit between its mammalian host and arthropod vector during tick feeding. Differential production of lipoproteins is essential for spirochaetes to survive, multiply and migrate within both hosts. Outer‐surface protein C (OspC), which is induced during the blood meal, is critical for transmission of Lyme disease spirochaetes by nymphal ticks. Its biological function is poorly understood, however, despite the fact that its crystal structure has been solved. Evidence has accumulated that OspC blocks clearance of spirochaetes following inoculation in skin, and it is thought to do so by facilitating evasion of innate immunity. The study by Liang and co‐workers in this edition of Molecular Microbiology extends this work by showing that OspC prevents early elimination and promotes dissemination. Surprisingly, they also show that unrelated borrelial outer‐surface lipoproteins can replace these functions in an ospC mutant. They propose that an abundance of lipoprotein(s) is needed to stabilize the borrelial outer membrane against innate defences. This provocative work clearly runs counter to prevailing orthodoxies of bacterial pathogenesis. It also points the way towards future studies that will clarify the ‘partially specific’ roles of this enigmatic molecule in Lyme disease pathogenesis.