Heavy metals like iron, copper, manganese and zinc can be toxic in large amounts. But in low concentrations, they are essential micronutrients for humans as well as bacteria. As part of the defense against invasive microbes, our immune system exploits this property by starving bacteria of the metals they need to survive. One way of doing this is with calprotectin, an immune defense protein produced by neutrophils at the site of infections. Calprotectin depletes the local environment of metal nutrients, and can block Borrelia burgdorferi growth. The mechanism of how this works has now been explained in a newly published study, funded by GLA and led by Dr. Valeria Culotta.
Calprotectin was found in the dermal and epidermal layers of erythema migrans rashes of early Lyme disease patients. It is believed that epithelial keratinocytes in the skin produce calprotectin, which is more commonly associated with neutrophils, immune cells that are absent in this particular site. Surprisingly, calprotectin blocked B. burgdorferi growth not by depleting metals, as would be expected. Instead, it directly bound to the bacteria and changed their shape from spirochetes into a cyst-like form, when immersed in water. This differs from calprotectin’s mechanism of blocking another bacteria, E. coli, in which metal sequestration is essential to blocking bacterial replication. These findings suggest a unique new pathway that could be explored for a potential therapeutic that is specific to B. burgdorferi.