Pulmonary fibrosis is a frequent consequence of chronic inflammatory processes and environmental expo- sures. Available antifibrotic therapies are inefficient. Data suggest that T cells are commonly present in the lungs of patients in association with fibrosis and express integrins, and that these integrins may be a master switch that defines a profibrotic or antifibrotic phenotype of T cells. The Overall Goal of this study is to clarify the mechanistic role of integrin-expressing T cells in the pro- and antifibrotic regulation in the lungs. The Spe- cific Hypothesis of this study is that the expression and functional activity of integrins 1V23, 1V25, 22- containing and 1E-containing integrins, on pulmonary T cells defines their regulatory phenotype (TGF-2+ simi- lar to Th3 and Tregs acting through membrane-bound TGF-2), persistence in the lung, and stimulation of col- lagen production. We further hypothesize that pulmonary infiltration of T cells that do not express integrins leads to a decrease in active TGF-2, elevated expression of TNF-1 and IFN-3, and subsequently to attenuation of collagen production. The following Specific Aims will be addressed. 1. Determine whether elevated expres- sion of integrins on pulmonary T cells is associated with a TGF-2-associated regulatory phenotype of T cells and with lower pulmonary function, whereas infiltration of T lymphocytes not expressing integrins is associated with inflammatory phenotype and higher pulmonary function in patients with interstitial lung disease. 2. Deter- mine whether elevated expression levels and functional activity of integrins on pulmonary T lymphocytes in the CCL18 overexpression model in vivo define a) their prolonged persistence in the lungs, b) the increased pro- duction, activation, and cell surface binding of TGF-2, and c) collagen accumulation. Determine whether partial neutralization of bleomycin-induced collagen accumulation by CCL18 overexpression is dependent on de- creased expression of 1V-containing integrins on pulmonary T lymphocytes, their decreased expression of ac- tive TGF-2, and elevation of TNF-1 and IFN-3. Determine whether these integrin-mediated pro- and antifibrotic mechanisms can be therapeutically modulated to regulate collagen accumulation in the lungs of experimental animals. 3. Determine whether 1V-, 22-, or 1E-containing integrins facilitate cell-cell interactions between pul- monary T cell and primary fibroblasts in vitro, the increase in TGF-2 production and/or activation, cell surface binding of TGF-2 by T cells, and stimulation of collagen production by fibroblasts in cell culture. Determine whether neutralization of the expression of integrins on T cells with siRNA or of the integrin function with neu- tralizing antibodies abrogate their regulatory phenotype and the profibrotic effect in co-cultures. Determine whether overexpression of 1V-containing integrins in pulmonary T cells derived from healthy volunteers causes changes toward regulatory profibrotic phenotype. Investigate the ability of CCL18 to directly modulate the phe- notype of normal human pulmonary T cells toward profibrotic, by stimulating the expression, activation, and cell surface binding of TGF-2, and expression of 1V-containing and 22-containing integrins. PUBLIC HEALTH RELEVANCE: Relevance of the Proposed Research to Veterans Health. Excessive scarring, or fibrosis, plays a pivotal role in various diseases of the lungs, liver, and kidneys, in wound granulation, arteriosclerosis and in chronic inflammation in all organs. New knowledge about mechanisms of fibrosis in one organ or disease may be broadly applicable to various diseases in which unwanted excessive scarring occurs. Scarring mechanisms in different diseases may share certain key pathologic components. For example, scarring of the lungs occurs in such diseases as scleroderma, rheumatoid arthritis, hypersensitivity pneumonitis, sarcoidosis, and idiopathic pulmonary fibrosis. Rates of lung fibrosis-associated deaths are even higher in the elderly and male populations, and those subjected to military exposures. These groups are abundantly represented in the veteran population. This proposal is broadly applicable to pulmonary medicine, inflammatory and immune abnormalities, autoimmunity, and immune-mediated fibrosis. Therefore, this research is applicable to the VA patient care mission, the designated priority areas of pulmonary disorders, autoimmune disorders, and wound healing and to the designated research area of chronic diseases.