TNF-α and IL-1β but not IL-18 counteract TGF-β1 mediated stimulation of collagen accumulation and increased extracellular matrix strength and stiffness

Cytokine-mediated cross-talk between immune cells and fibroblasts is a driver of excessive ECM accumulation during fibrosis. In this study, we used a 3D in vitro model of a connective tissue to discern the roles of three pro-inflammatory cytokines; TNF-α, IL-18 and IL-1β, alone, and in combination with TGF-β1 to simulate the fibrotic environment. Ring-shaped tissues were formed by seeding human fibroblasts into circular molds of agarose, wherein the cells self-assembled, formed a 3D tissue and synthesized de novo a collagen-rich ECM. Cytokine treated tissues were analyzed at days 7 and 14 by histology and measured for thickness, collagen, DNA and strength and stiffness by tensile testing. Despite their pro-inflammatory nature, none of the cytokines increased collagen alone or in combination with TGF-β1. TNF-α and IL-1β reduced collagen, tissue strength and stiffness, and altered tissue morphology. When combined with TGF-β1, TNF-α and IL-1β counteracted TGF-β1-mediated increases in collagen, strength, and stiffness. In contrast, IL-18 had minimal effects alone or when combined with TGF-β1. These data suggest that IL-18 has no effect on fibroblast activation, whereas TNF-α and IL-1β may modulate TGF-β1's effects. This 3D model of a human collagen-rich tissue can help define cytokine-mediated cross-talk between immune cells and fibroblasts.