Methods: We assessed the frequencies and functional capacities of ILC2 in the bone marrow, lung, skin, and mesenteric lymph nodes of WT, IL-33-deficient, and/or ST2-deficient mice by flow cytometry.
Results: We identified that deficiency in IL-33 signaling lead to an accumulation of ILC2 in the bone marrow and a decrease in ILC2 in the lungs, skin, and mesenteric lymph nodes compared to wild type mice. These bone marrow and peripheral tissue ILC2 frequencies were established by an ILC2 cell-intrinsic mechanism. Absent IL-33 signaling did not appreciably affect the capacity of bone marrow ILC2 to proliferate or secrete canonical ILC2-associated cytokines. However, lack of IL-33 signaling significantly altered the chemokine receptor profile on bone marrow ILC2, with ST2-deficient ILC2 overexpressing Cx3cr1, Ccr7, Ccr9, Cxcr4, and Ptgdr2 compared to wild type ILC2. Treatment of wild type ILC2 with IL-33 ex vivodecreased the expression of CXCR4, a major chemotactic signal for the retention of cells in the bone marrow. Moreover, pharmacologic blockade of CXCR4 induced mobilization of ILC2 from the bone marrow of ST2-deficient mice.
Conclusions: These data suggest a mechanism by which IL-33 negatively regulates CXCR4 expression on developing ILC2 leading to efficient egress of these cells from the bone marrow.