Monocyte chemoattractant protein-1 expression by osteoblasts following infection with Staphylococcus aureus or Salmonella

Two common pathogens of bone, Staphylococcus aureus and Salmonella, were in vestigated for their ability to induce chemokine expression in bone-forming osteoblasts, Cultured mouse or human osteoblasts could rapidly respond to bacterial infection by upregulating the mRNA encoding the chemokine, monocy te chemoattractant protein-1 (MCP-1). This rapid induction occurred on infe ction with either the gram-positive pathogen, S. aureus, or the gram-negati ve pathogen, Salmonella, Increased mRNA expression translated into MCP-1 se cretion by cultured mouse or human osteoblasts in response to viable bacter ia, whereas UV-killed bacteria were less effective in stimulating chemokine secretion. There was a dose-response relationship observed between the amo unt of input bacteria and increases in MCP-1 secretion. Immunohistochemical staining of infected osteoblasts indicated that the majority of cells coul d express MCP-1, with some osteoblasts having a higher intensity of stainin g than others. Organ cultures of mouse calvaria (skullcap) bone showed incr eases in MCP-1 immunostaining following bacterial infection. The immunoreac tive MCP-1 in infected calvaria localized to areas containing active osteob lasts. Taken together, these studies demonstrate a conserved osteoblast-der ived MCP-1 response to two very different pathogens of bone.