Human bone allografts can induce T cells with high affinity for donor antigens.

We analysed the cellular immune response in ten transplantations of different massive bone allografts, of which five had a poor clinical outcome. Cytotoxic T lymphocytes (CTL) and T helper lymphocytes (TH) against mismatched donor antigens were found in all patients. More importantly, CTL with a high affinity for donor antigens were found in five cases. High-affinity CTL need no CD8 molecule to stabilise the antigen binding and are strongly associated with rejection of heart and corneal transplants. Even after removal of most of the bone-marrow cells, we found high-affinity CTL and high TH frequencies. This T-cell response could be detected over a period of years. We conclude that frozen bone allografts can induce high-affinity donor-specific CTL. The present assay allows qualification and quantification of the levels of CTL and TH in the blood. This approach may be helpful in studying the effect of the immune response on the outcome of the graft.

A new software correction approach to volume averaging artifacts in CT.

The nature of artifacts in computed tomography, due to nonlinear partial volume effects, is briefly reviewed. A methodology for correction of these artifacts proposed. This methodology utilizes a correction algorithm for post-processing the original reconstructed CT image. The algorithm utilizes local CT values to predict the probability of volume averaging of bone, air and tissue, and incorporates information from the original image on the spatial extent of the averaging, to correct the nonlinear effects. The algorithm is successfully demonstrated on mathematical phantoms, wherein volume averaging can be introduced over central targets and/or peripheral annuli of tissue, bone, and air. The algorithm is also demonstrated on actual CT brain scans but only for its qualitative effects. It is pointed out that higher order corrections, to be reported in future publications, will further correct the actual clinical scans.