CCL2 and susceptibility to pneumonia measurement: Increased transcription of chemokine receptors CCR2 (CCL2/monocyte chemoattractant protein-1 (MCP-1) receptor) and CCR5 (CCL3/MIP-1A receptor) were observed (Table S4), indicating that these inflammatory signals were activated, but receptors XCR1, CCR4, and ACKR3 were downregulated in the pneumonia group.