CCL2 and susceptibility to pneumonia measurement: In the pathogenesis of pneumonia, MCP-1 binds to its unique receptor chemokine C–C motif receptor (CCR2) to induce downstream signaling pathways [32,33] and has been demonstrated to be a powerful T cell and monocyte/macrophage chemoattractant against bacteria infecting the lung [34,35,36,37,38].