Structure at 1.44 A resolution of an N-terminally truncated form of the rat serum complement C3d fragment.

Complement component C3 plays a key role in the complement-mediated immune defence, and occupies a central position within the complement cascade system. One of its degradation products, C3dg, was purified from rat serum and crystallised in two different crystal forms as N-terminally truncated fragment. Despite the truncation and the lack of a significant portion of the N-terminus as compared to C3d, the structure of the fragment is highly similar to that of recombinant human C3d (Nagar et al., Science 280 (1998) 1277-1281). Structural details of the reactive site have been obtained, suggesting a possible mode of thioester bond formation between Cys-1010 and Gln-1013 and thioester bond cleavage in the transacylation reaction involving His-1126. The truncation at the N-terminus of C3d leads to the exposure of a surface of the molecule that favours dimerisation, so that in both crystal forms, the fragment is present as a dimer, with monomers related by a two-fold axis.

Evaluation of the scintigraphic technique for detecting bone metastases in 100 breast cancer patients.

In an attempt to evaluate the utility of bone scintigraphy for the diagnosis and follow-up of skeletal metastases, radioisotopic scan (total body) by 99mTc has been performed on 100 patients suffering from breast cancer in various stages. The radiographic control followed the scan on the basis of clinical or scintigraphic suspicion of bone lesions. Twenty-one patients showed metastases by scan, and in all but 2 the radiography was concordantly positive; in 22 subjects scintigraphy and radiology demonstrated non-malignant lesions. Both scan and radiology were used to explore 169 metastatic localizations, with concordant results in 45% of the sites; however, 7% of the sites with discordant results became positive for metastasis by radiology some months after the scan positivity. The false-negative results were more frequent in the radiographic study (27%) than with the scintigraphic scan (21%). The latter technique was unable to detect osteoblastic lesions in particular. The scintigraphic test also gave reliable results in the follow-up procedure, frequently anticipating the radiological modifications of metastatic lesions. In conclusion, bone scan often appears to be more accurate and preocious than the roentgengraphic test in the detection and the follow-up of skeletal metastatic lesions; it suggests the utility of the bone scan as a preliminary test, which allows a more rational use of the radiology.