[Reduction of the immunological rejection in composite tissue allotransplantation by heat stress preconditioning]

BACKGROUND

In spite of great advances in the field of composite tissue allotransplantations (CTA), there is still a major need for optimisation in terms of immunosuppression. Heat shock proteins are produced as a reaction of the body during a stress situation. Once elevated, they protect against a second stress and reduce ischaemia-reperfusion injury within transplantations. In the literature the effect of heat shock and HSP70 on rejection after CTA has not been described. The purpose of this experimental study was to examine the effect of heat shock proteins on rejection in a rat model of CTA. Evaluated was the effect of preconditioning by prior heat stress.

METHODS AND MATERIALS

Brown Norway rats were systemically heated to a core temperature of 42 °C in order to up-regulate HSP70. The expression of HSP70 in muscle was measured by Western blot analysis and showed a peak 24 h after heat shock. Allogeneic hindlimb transplantations were performed between Brown Norway rats (donor) and Lewis rats (recipients). Group 1 (n=12) was preheated 24 h prior to transplantation. In group 2 (n=12) the transplantation was performed without prior heat shock. Group 3 (n=6) was used as a control group with syngeneic hindlimb transplantations between Lewis rats. Postoperatively the appearance of the transplanted hindlimb was evaluated every 12 h. The beginning of rejection was defined when plantar erythema and foot oedema could be observed at the same time. To verify these discrete signs of rejection, the observation was continued for a further 24 h. In this time erythema and oedema spread over the whole transplanted hindlimb. The rat was sacrificed after specimens of skin and muscle had been taken for histological assessment.

RESULTS

The rejection in group 1 (with preconditioning heat shock) began after 4.83±0.44 days, in group 2 (without heat shock) already after 3.88±0.53 days. The difference between these groups was significant because of the small standard deviation (Whitney-Mann U test: p<0.01).

CONCLUSION

In our model of allogeneic composite tissue transplantation, a heat shock and subsequent up-regulation of HSP70 led to a significant delay of the immunological rejection. As the graft rejection is an important item influencing the outcome of allogeneic transplantations, these results represent an option to improve the final functional outcome of composite tissue allotransplantations.

Mikrochirurgische Rekonstruktion der oberen Extremität nach Brandverletzungen

BACKGROUND

Free tissue transplantation is a rarely indicated procedure in burn reconstruction. As the versatility and variability of free flaps have significantly increased during recent years, so too have the indications for these procedures expanded.

MATERIAL AND METHODS

We retrospectively report the results of 42 free flaps for upper extremity reconstruction in 35 severely burned patients using 13 different free flaps. This experience has enabled us to establish reconstructive principles pertinent to the type of injury (burn versus high voltage injuries) and the timing of reconstruction procedures.

RESULTS

In high voltage injuries (n = 17) early free flap coverage (< 21 days after trauma) with muscular flaps was the most frequently used type of reconstruction. Reconstruction site was predominately the forearm. In burn injuries (flame, contact, fluid), free flap coverage was performed during a later stage of the treatment course (3 to 6 weeks after trauma), or as a secondary procedure. Reconstruction with cutaneous or fascial flaps was the preferred method. The elbow and the dorsum of the hand underwent defect coverage in most circumstances. For the reconstruction of complex or large defects (n = 6) combined "chimeric" flaps, preexpansion of free flaps, or the combination of a free and local flap were used. Overall, the flap failure rate was 12 % (n = 5). Interestingly, there was a relationship between flap failure rate and timing of the procedure. Four out of five flap failures occurred within 5 to 21 days after trauma, all five flap failures occurred between five days and six weeks. No flap failure was seen during secondary reconstruction.

CONCLUSION

Our data demonstrate that burn and high voltage injuries are distinct entities, each requiring custom-tailored reconstructive solutions for limb salvage. Even if our flap failures all occurred during the first six weeks it should not be forgotten that this type of coverage is the only alternative to amputation in selective cases.