CCL18 Expression and Production by Human Alveolar Macrophages in Co-Culture with Lung Fibroblasts

CCL18 is a C-C chemokine produced by human DC and alternatively activated macrophages, and it has been shown that CCL18 augments collagen production by human fibroblasts in vitro (Atamas S.P. et al., 2003). We investigated the interaction of human lung fibroblasts (FBR) and alveolar macrophages (AM) concerning CCL18 production. In a co-culture system consisting of AM layered over human lung FBR in the presence of IL-4, IL-10 or their combination, CCL18 production by AM was significantly higher in FBR-AM co-culture than in AM alone. Additionally, FBR strongly enhanced the up-regulatory effect of IL-4 and IL-10 on CCL18 expression and production by AM in vitro. Immunolocalization with anti-CCL18 Ab of cells producing CCL18 in the FBR-AM co-culture revealed that AM, but not FBR, displayed a strong positive signal for CCL18. Experiments with cells separated by non cell permeable membrane showed that two important components are responsible for this effect: direct contact of AM with FBR and/or extracellular matrix components and soluble mediator(s) released by FBR. The effect of FBR-AM co-culture can be substituted by AM culture alone on collagen coated surface adding conditioned medium from FBR in the presence of IL-4 and/or IL-10. The collagen/IL-4/IL-10-induced level of CCL18 was diminished by blocking of β2-integrins with anti-CD18 mAb in the presence of serum. The co-culture of AM with airway epithelial cells or autologous T-cells did not change the levels of CCL18 production by AM. Other cytokines tested, which may have relevance to pulmonary fibrosis, did not significantly modulate the level of CCL18 production by AM in vitro. Our data reveal the importance of lung fibroblasts and alveolar macrophages interactions in the complex milieu of pulmonary inflammation and fibrosis.