Increased expression of MHC class I in the indoor environment was accompanied by the upregulation of a plethora of chemokines, including CCL2, CCL8, CCL28, CCR1, CXCR4 and CXCL12. Chemokines are chemotactic cytokines that function during immune responses to recruit effector cells to sites of inflammation and infection. This evidence concerns the gene CXCR4 and infection.