This investigation examines the influence of α-toxin (Hla) expression by CA-MRSA on host immune cell integrity and cytokine expression during infection of human blood. Flow cytometry analysis of human blood infected by Staphylococcus aureus PFGE type USA300 or a USA300Δhla demonstrated that Hla expression significantly increased plasma membrane permeability of human CD14(+) monocytes. The increased susceptibility of human CD14(+) monocytes to Hla toxicity paralleled the high cell-surface expression on these cell types of ADAM10. USA300 rapidly associated with PMNs and monocytes but not T cells following inoculation of human blood. Transcription analysis indicated a strong up-regulation of proinflammatory cytokine transcription following infection of human blood by USA300 and USA300Δhla. CBAs and ELISAs determined that IL-6, IL-10, TNF-α, IFN-γ, IL-1β, IL-8, and IL-4 are significantly up-regulated during the initial phases of human blood infection by USA300 relative to mock-infected blood but failed to distinguish any significant differences in secreted cytokine protein concentrations during infection by USA300Δhla relative to USA300. Collectively, these findings demonstrate that expression of Hla by USA300 has a significant impact on human CD14(+) monocyte plasma membrane integrity but is not exclusively responsible for the proinflammatory cytokine profile induced by USA300 during the initial stages of human blood infection.
Keywords: Staphylococcus aureus; T cell; chemokine; monocyte; pathogenesis; virulence.