Acute Rejection of Knee Joint Articular Cartilage in a Rat Composite Tissue Allotransplantation Model.

BACKGROUND: Osteochondral allograft transplantation is used to treat severe cartilage injury or chondral defects, with good outcomes in clinical studies. However, allograft chondrocyte death due to apoptosis may occur during storage or as a result of implantation stress. We investigated a third possible cause, chondrocyte apoptosis resulting from an immune response, by means of composite tissue allografting, thus eliminating the role of storage and implantation stresses on osteochondral grafts. METHODS: Vascularized composite tissue allotransplantation (from Fisher 344 to Lewis rat strains) and isotransplantation (from Lewis to Lewis strains) of rat hind limbs were performed. Immunohistochemistry was performed with use of caspase-3 and TUNEL (terminal deoxynucleotidyl transferase mediated dUTP nick end labeling) assays. Analyses were performed immediately after perfusion (day zero) and on postoperative days one, three, seven, twelve, and eighteen (n = 5 for immunohistochemistry). Transmission electron microscopy was used for detection of chondrocyte apoptosis. Laser capture microdissection followed by quantitative real-time polymerase chain reaction assays was used for analysis of postoperative caspase-3 gene expression. RESULTS: Caspase-3 immunochemistry was increasingly positive in allograft chondrocytes from postoperative day seven onward. In contrast, caspase-3 gene expression decreased in all allografts. TUNEL assays showed increasing apoptosis of allograft chondrocytes, and electron microscopy also revealed evidence supporting the development of apoptosis. CONCLUSIONS: Immunorejection of chondrocytes in transplanted cartilage has been thought to be unlikely, but our data reveal that chondrocytes can undergo apoptosis in allotransplantation. This apoptosis involves the caspase-3 cascade and indicates that chondrocytes may induce acute rejection.

Neutrophil-derived tumor necrosis factor-α contributes to acute wound healing promoted by N-(3-oxododecanoyl)-L-homoserine lactone from Pseudomonas aeruginosa.

BACKGROUND: Pseudomonas aeruginosa is frequently isolated from chronic wounds and causes serious infection in immunocompromised hosts. N-(3-Oxododecanoyl)-L-homoserine lactone (3-oxo-C12-HSL) is synthesized by an autoinducer synthase encoded by the bacterial lasI gene in P. aeruginosa, which regulates the production of virulence factors and biofilm formation in this bacterium. Recent studies have suggested that 3-oxo-C12-HSL contributes to the modulation of immune responses. However, the effect of this molecule on wound healing in P. aeruginosa infection remains to be elucidated. OBJECTIVE: We used an animal model to study the effect of 3-oxo-C12-HSL on wound healing in skin infected with P. aeruginosa. METHODS: Wounds were created on the backs of Sprague-Dawley (SD) rats and the P. aeruginosa strain PAO1 (PAO1) or its lasI deletion mutant (ΔlasI) was inoculated onto the wound surface. To examine the biological activity of 3-oxo-C12-HSL, rats were injected intraperitoneally with anti-3-oxo-C12-HSL antiserum or administered 3-oxo-C12-HSL at the wound surface. The wound tissues were harvested for analysis of the healing process and inflammatory response. RESULTS: PAO1 inoculation significantly accelerated the wound healing and inflammatory response on day 3 post-wounding. These responses were reversed by inoculation with ΔlasI instead of PAO1 or treatment with anti-3-oxo-C12-HSL antiserum. In contrast, administration of 3-oxo-C12-HSL in the absence of PAO1 significantly promoted these responses, which were suppressed by the anti-TNF-α mAb. CONCLUSION: These results strongly suggest that 3-oxo-C12-HSL may be involved in healing wounds infected with P. aeruginosa through induction of inflammatory responses.