The Src-Family Kinases Hck and Fgr Regulate Early Lipopolysaccharide-Induced Myeloid Cell Recruitment into the Lung and Their Ability To Secrete Chemokines.

Myeloid leukocyte recruitment into the lung in response to environmental cues represents a key factor for the induction of lung damage. We report that Hck- and Fgr-deficient mice show a profound impairment in early recruitment of neutrophils and monocytes in response to bacterial LPS. The reduction in interstitial and airway neutrophil recruitment was not due to a cell-intrinsic migratory defect, because Hck- and Fgr-deficient neutrophils were attracted to the airways by the chemokine CXCL2 as wild type cells. However, early accumulation of chemokines and TNF-α in the airways was reduced in hck(-/-)fgr(-/-) mice. Considering that chemokine and TNF-α release into the airways was neutrophil independent, as suggested by a comparison between control and neutrophil-depleted mice, we examined LPS-induced chemokine secretion by neutrophils and macrophages in wild type and mutant cells. Notably, mutant neutrophils displayed a marked deficit in their capability to release the chemokines CXCL1, CXCL2, CCL3, and CCL4 and TNF-α in response to LPS. However, intracellular accumulation of these chemokines and TNF-α, as well as secretion of a wide array of cytokines, including IL-1α, IL-1ß, IL-6, and IL-10, by hck(-/-)fgr(-/-) neutrophils was normal. Intriguingly, secretion of CXCL1, CXCL2, CCL2, CCL3, CCL4, RANTES, and TNF-α, but not IL-1α, IL-1ß, IL-6, IL-10, and GM-CSF, was also markedly reduced in bone marrow-derived macrophages. Consistently, the Src kinase inhibitors PP2 and dasatinib reduced chemokine secretion by neutrophils and bone marrow-derived macrophages. These findings identify Src kinases as a critical regulator of chemokine secretion in myeloid leukocytes during lung inflammation.

Fgr deficiency results in defective eosinophil recruitment to the lung during allergic airway inflammation.

Using a mouse model of allergic lung inflammation, we found that mice deficient of Fgr, a Src family tyrosine kinase highly expressed in myelomonocytic cells, fail to develop lung eosinophilia in response to repeated challenge with aerosolized OVA. Both tissue and airway eosinophilia were markedly reduced in fgr(-/-) mice, whereas mice with the sole deficiency of Hck, another Src family member, responded normally. Release of allergic mediators, such as histamine, IL-4, RANTES/CCL5, and eotaxin/CCL11, in the airways of OVA-treated animals was equal in wild-type and fgr(-/-) mice. However, lung eosinophilia in Fgr-deficient mice correlated with a defective accumulation of GM-CSF and IL-5 in the airways, whereas secretion of these cytokines by spleen cells in response to OVA was normal. Examination of mRNA expression in whole lung tissue allowed us to detect comparable expression of transcripts for eotaxin/CCL11, macrophage-inflammatory protein-1 alpha/CCL3, macrophage-inflammatory protein-1 beta/CCL4, monocyte chemoattractant protein-1/CCL2, TCA-3/CCL1, IL-4, IL-10, IL-2, IL-3, IL-9, IL-15, and IFN-gamma in OVA-sensitized wild-type and fgr(-/-) mice. In contrast, the increase in IL-5 and IL-13 mRNA expression was lower in fgr(-/-) compared with wild-type mice. These findings suggest that deficiency of Fgr results in a marked reduction of lung eosinophilia and the establishment of a positive feedback loop based on autocrine secretion of eosinophil-active cytokines. These results identify Fgr as a novel pharmacological target to control allergic inflammation.