Temporal and spatial immunolocalization of cytokines in murine chronic granulomatous tissue. Implications for their role in tissue development and repair processes

Abstract

Background: Cytokines have profound effects on various aspects of granulomatous tissue formation. However, there is little information regarding their distribution during tissue development. This study investigated the temporal and spatial distribution of transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), tumor necrosis factor-alpha (TNF-alpha), interleukin-1 alpha (IL-1) and IL-1 beta in developing granulomatous tissue.

Experimental design: Murine chronic granulomatous air pouches were induced and full thickness biopsies taken at intervals up to 28 days. Samples were prepared for immunohistochemistry and labeled using antibodies against TGF-beta, bFGF, PDGF, EGF, TNF-alpha, IL-1 alpha and IL-1 beta.

Results: Immunoreactivity to TGF-beta, PDGF, TNF-alpha, IL-1 alpha and IL-1 beta was localized to a proportion of macrophages within the granulomatous tissue. Immunopositive macrophage numbers increased with time, and with the exception of PDGF were associated with areas of fibrogenesis between days 14 to 28. Heterogeneous labeling of capillaries for EGF was observed within the granulomatous tissue juxtaposed to dermal musculature. Diffuse labeling of bFGF, associated with extracellular matrix, was always observed. After day 14, bFGF immunoreactivity was discretely localized to endothelial cells and the basement membrane of vessels within the granulomatous tissue. TGF-beta immunoreactivity was also associated with extracellular matrix components, being most intense in the area of fibrogenesis between 14 and 28 days. Occasional fibroblasts were also labeled with TGF-beta in this region.

Conclusions: The spatial and temporal confinement of the individual cytokines suggests that a sequential coordinated process of repair and fibrosis is occurring. It is hoped that these observations will provide a more effective therapeutic approach for the sequential application of cytokines in abnormalities of wound healing.