GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR IN STAPHYLOCOCCUS AUREUS-INDUCED ARTHRITIS

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokin e that is able to increase not only the production of phagocytic cells but also their efficacy with respect to, e.g., bactericidal propertie s. In this study, we wanted to analyze the impact of GM-CSF on experim ental Staphylococcus aureus-induced arthritis. For that purpose, mice were administered GM-CSF before and after bacterial inoculation. Altho ugh there was an increase in the total number of leukocytes as well as in the granulocyte fraction, there was no favorable effect on the sev erity of arthritis or on survival rates. There were no obvious differe nces between the GM-CSF-pretreated animals and controls with regard to growth of staphylococci in joints and kidneys 4 days after the bacter ial inoculation. In contrast, mice that had been pretreated with GM-CS F prior to bacterial inoculation showed approximately four times lower numbers of bacteria in their blood 24 h later. These results, along w ith those of our previous studies, suggest that on the one hand the gr anulocyte is the main protective cell during the course of S. aureus i nfection but that on the other hand, upregulation of granulocyte-macro phage production will not exert any additional protective effects with respect to tissue injury.