Antifibrotic effects of IL-12-treated natural killer cells on collagen type I regulation in lung fibroblasts

Idiopathic pulmonary fibrosis is a chronic fibrotic lung disease with limited treatment options, making the development of new therapies crucial. We previously demonstrated that γδ T cells, a subset of immune effector cells, exhibit antifibrotic properties. We have also shown that natural killer (NK) cells, another class of immune effectors, can be efficiently expanded in culture using interleukin-2 (IL-2) and interleukin-18 (IL-18). This study examined the effects of interleukin-12 (IL-12)-stimulated NK cells, expanded with IL-2 and IL-18, on type I collagen and α-smooth muscle actin (αSMA) expression in pulmonary fibroblasts. IL-12-stimulated human NK cells exhibited reduced cytotoxicity toward pulmonary fibroblasts while retaining their proliferative capacity. Co-culture of IL-12-stimulated NK cells with fibroblasts significantly suppressed type I collagen and αSMA expression, even without direct cell contact, indicating the involvement of soluble factors. Supernatants from IL-12-stimulated NK cells partially inhibited the expression of these antifibrotic factors, suggesting a dual mechanism: direct cell-cell interaction and soluble factor secretion. Interferon-γ (IFN-γ) in the supernatant significantly increased, and neutralizing anti-IFN-γ monoclonal antibody partially reversed type I collagen and αSMA suppression. Similarly, IL-12-stimulated murine NK cells suppressed type I collagen in mouse pulmonary fibroblasts. These findings suggest that IL-12-stimulated NK cells inhibit the expression of fibrosis-associated molecules via contact-dependent and -independent mechanisms, supporting their potential for adoptive cell therapy in pulmonary fibrosis.