CXCL12 and infection: 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.