β2 integrins rather than β1 integrins mediate Alternaria-induced group 2 innate lymphoid cell trafficking to the lung

Background: Group 2 innate lymphoid cells (ILC2s) expand in the lungs of mice during type 2 inflammation induced by the fungal allergen Alternaria alternata. The increase in ILC2 numbers in the lung has been largely attributed to local proliferation and whether ILC2s migrate from the circulation to the lung after Alternaria exposure is unknown. Objective: We examined whether human (lung, lymph node, and blood) and mouse lung ILC2s express beta(1) and beta(2) integrin adhesion molecules and whether these integrins are required for trafficking of ILC2s into the lungs of mice. Methods: Human and mouse ILC2s were assessed for surface expression of beta(1) and beta(2) integrin adhesion molecules by using flow cytometry. The role of beta(1) and beta(2) integrins in ILC2 trafficking to the lungs was assessed by in vivo blocking of these integrins before airway exposure to Alternaria in mice. Results: Both human and mouse lung ILC2s express high levels of beta(1) and beta(2) integrin adhesion receptors. Intranasal administration of Alternaria challenge reduced ILC2 numbers in the bone marrow and concurrently increased blood and lung ILC2 numbers. In vivo blocking of beta(2) integrins (CD18) significantly reduced ILC2 numbers in the lungs but did not alter ILC2 proliferation, apoptosis, and function. In contrast, in vivo blocking of beta(1) integrins or alpha(4) integrins did not affect lung ILC2 numbers. Conclusion: ILC2 numbers increase in the mouse lung not only through local proliferation but also through trafficking from the circulation into the lung using beta(2) rather than beta(1) or alpha(4) integrins.