Our previous studies reported the performance of Macroporous Biphasic Calcium Phosphate (MBCP) in spine fusion. In the present study, this material was used in block forms in selected patients with tumoral resection in long bone. Two cases were chosen with large benign bone tumors. Clinical and radiographic assessments, CT scans, and NMR were performed after 16 months, and in one case control biopsies were taken. In order to understand the kinetic process of biodegradation of the MBCP blocks and bone formation at the expense of the ceramics, an experimental study in surgically created bond defects in canine femoral cortices was made. The MBCP blocks recovered after implantation period from 2 to 18 weeks were analyzed using histological, stereological, ultrastructural, electron microprobe, and IR spectroscopy analyses. This study demonstrated the efficiency of MBCP blocks for filling pathological defects in human long bone. The biointegration process of the MBCP blocks was due to a partial dissolution of the ceramics crystals (b-TCP content) by multinucleated cells. Simultaneously, bone ingrowth at the expense of the ceramic is observed. The new bone formation inside the MBCP macropores and in the spaces between the blocks, involved the formation of a new cortical bone on the outer part, and a trabecularlike bone with bone marrow in the inner part of the implant. The biological resorption of the MBCP ceramic decreased after 1 month implantation in dog, due to the protective role of the newly formed lamellar bone on the surface and in the core of the ceramics.

We report the existence of eight different interleukin-15 receptor ␣-chain (IL-15R␣) transcripts resulting from exon-splicing mechanisms within the IL-15R␣ gene. Two main classes of transcripts can be distinguished that do or do not (⌬2 isoforms) contain the exon 2-coding sequence. Both classes were expressed in numerous cell lines and tissues (including peripheral blood lymphocytes) at comparable levels and could be transcribed in COS-7 cells, and the proteins were expressed at the cell surface. Both receptor forms displayed numerous glycosylation states, reflecting differential usage of a single N-glycosylation site as well as extensive O-glycosylations. Whereas IL-15R␣ bound IL-15 with high affinity, ⌬2IL-15R␣ was unable to bind IL-15, thus revealing the indispensable role of the exon 2-encoded domain in cytokine binding. A large proportion of IL-15R␣ was expressed at the nuclear membrane with some intranuclear localization, supporting a potential direct action of the IL-15⅐IL-15R␣ complex at the nuclear level. In sharp contrast, ⌬2IL-15R␣ was found only in the non-nuclear membrane compartments, indicating that the exon 2-encoded domain (which is shown to contain a potential nuclear localization signal) plays an important role in receptor post-translational routing. Together, our data indicate that exon 2 splicing of human IL-15R␣ is a natural process that might play regulatory roles at different levels.

Leukemia inhibitory factor (LIF) is a multifunctional cytokine belonging to the interleukin-6 subfamily of helical cytokines, all of which use the glycoprotein (gp) 130 subunit for signal transduction. The specific receptor for LIF, gp190, binds this cytokine with low affinity and is also required for signal transduction. We have recently reported that glycosylated LIF produced by transfected Chinese hamster ovary cells also binds to a lectin-like receptor, mannose 6-phosphate/insulin-like growth factor II receptor (Man-6-P/IGFII-R) (Blanchard, F., Raher, S., Duplomb, L., Vusio, P., Pitard, V., Taupin, J. L., Moreau, J. F., Hoflack, B., Minvielle, S., Jacques, Y., and Godard, A. (1998) J. Biol. Chem. 273, 20886 -20893). The present study shows that (i) mannose 6-phosphatecontaining LIF is naturally produced by a number of normal and tumor cell lines; (ii) other cytokines in the interleukin-6 family do not bind to Man-6-P/IGFII-R; and (iii) another unrelated cytokine, macrophage-colonystimulating factor, is also able to bind to Man-6-P/IG-FII-R in a mannose 6-phosphate-sensitive manner. No functional effects or signal transductions mediated by this lectin-like receptor were observed in various biological assays after LIF binding, and mannose 6-phosphate-containing LIF was as active as non-glycosylated LIF. However, mannose 6-phosphate-sensitive LIF binding resulted in rapid internalization and degradation of the cytokine on numerous cell lines, which suggests that Man-6-P/IGFII-R plays an important role in regulating the amounts of LIF available in vivo.

Comparison of the binding properties of non-glycosylated, glycosylated human leukemia inhibitory factor (LIF) and monoclonal antibodies (mAbs) directed at gp190/LIF-receptor ␤ subunit showed that most of the low affinity (nanomolar) receptors expressed by a variety of cell lines are not due to gp190. These receptors bind glycosylated LIF produced in Chinese hamster ovary cells (CHO LIF) (K d ‫؍‬ 6.9 nM) but not Escherichia coli-derived LIF or CHO LIF treated with endoglycosidase F. CHO LIF binding to these receptors is neither affected by anti-gp190 mAbs nor by anti-gp130 mAbs and is specifically inhibited by low concentrations of mannose 6-phosphate (Man-6-P) (IC 50 ‫؍‬ 40 M), suggesting that they could be related to Man-6-P receptors. The identity of this LIF binding component with the Man-6-P/insulin-like growth factor-II receptor (Man-6-P/IG-FII-R) was supported by several findings. (i) It has a molecular mass very similar to that of the Man-6-P/IG-FII-R (270 kDa); (ii) the complex of LIF cross-linked to this receptor is immunoprecipitated by a polyclonal anti-Man-6-P/IGFII-R antibody; (iii) this antibody inhibits LIF and IGFII binding to the receptor with comparable efficiencies; (iv) soluble Man-6-P/IGFII-R purified from serum binds glycosylated LIF (K d ‫؍‬ 4.3 nM) but not E. coli LIF. The potential role of Man-6-P/IGFII-R in LIF processing and biological activity is discussed. Leukemia inhibitory factor (LIF)1 is a multifunctional, highly glycosylated soluble protein belonging to the interleukin-6 (IL-6) subfamily of helical cytokines (also including IL-11, oncostatin M (OSM), ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1)) (1-3). Signal transduction by these cytokines is proposed to result from cytokine-mediated homodimerization of the gp130 signal transducer (4) or heterodimerization of gp130 with another signal transducing subunit. IL-6 first binds with low affinity (nanomolar) to a specific IL-6R␣ subunit and the complex then recruits and homodimerizes two gp130 subunits for signaling. A final hexameric complex of two molecules each of IL-6, IL-6R␣, and gp130 has been proposed (5). Similarly, specific IL-11R␣ subunits have also been identified (6, 7) and the IL-11/IL-11R␣ complex is also proposed to induce homodimerization of gp130 for signaling. Other members of this cytokine family can induce heterodimerization of gp130 with gp190, a signaling molecule initially identified as the low affinity (nanomolar) LIF receptor (or LIF-R␤) (8). CNTF recruits gp130 and gp190 together with a third cytokine specific receptor chain (CNTF-R␣). LIF and OSM have been proposed to require only gp130 and gp190 to form a common signaling complex designated type I OSM receptor. Another type of OSM receptor, not used by LIF, has been described (type II OSM receptor). It involves the recruitment of gp130 with a recently identified gp180 transducing molecule also called OSM-R␤ (9). Cross-linking studies have also suggested that another receptor subunit besides gp130 and gp190 might participate in the structu...

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