Bone is a highly specialized form of connective tissue, composed of bone forming osteoblasts and bone-resorbing osteoclasts, several types of matrix proteins and proteoglycans, and bone salts of calcium and phosphorus. It not only forms the skeleton or framework of the bodies, but serves as a calcium reservoir in most vertebrates. The newest knowledge on bone cell biology has allowed us to consider the mechanisms of bone formation and resorption and their coupling system. A great number of such systemic hormones as 1 α, 25-dihydroxyvitamin D₃, parathyroid hormone and calcitonin and local factors including prostaglandins, interleukins, transforming growth factors, insulin-like growth factors and bone morphogenetic protein have been shown to be involved in the regulation of bone formation and resorption.
In this review, we will summarize the newest knowledge on bone cell biology to understand the pathogenesis of several metabolic bone diseases including osteoporosis, rheumatoid arthritis and inflammatory periodontal diseases.

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Human C-reactive protein (CRP), a typical acute-phase protein, increases about hundreds-fold in concentration in response to infection, inflammation or tissue injury.
CRP was first described by Tillet and Francis in 1930 as a serum protein capable of precipitating pneumococcal C-polysaccharide where phosphorylcholine (PC) was identified later to be a ligand. Clinical and biological aspects, especially immunological ones, of human CRP have been studied. And some of them have been ascribed to its capacity of ligand-binding with PC calcium-dependently. While type 4 pneumococcal polysaccharide which lacks phosphate and choline has been pointed out to be able to bind human CRP in calcium-dependent manner, ligands other than PC should be considered besides PC.
We find specific affinity chromatography bearing new ligand of negatively-charged aminocaproic acid which binds human CRP calcium-dependently (buffer ; 0.15 M NaCl, 0.02 M Tris, 0.01 M CaCl₂, 0.01 M NaN₃, pH 7.8, room temp.), being almost comparable to PC-affinity chromatography. In addition, another specific ligand of positively-charged aminohexyl-agarose is found to bind human CRP calcium-independently (buffer; 0.09 M NaCl, 0.01 M Tris, pH 7.4, room temp.) . These new ligands may provide simple model to understand human CRP.
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We have previously demonstrated the involvement of platelet-activating factor (PAF), which was newly generated by resident mononuclear cells with PMA-stimulation, in the rat pleurisy induced by phorbol myristate acetate (PMA) .
In the present study, we examined the mechanism of PAF production by mononuclear cells stimulated with PMA. Mononuclear cells from normal SD rats were incubated with PMA (1μM) at 37°C in the presence or absence of inhibitors. After a certain time of incubation, medium and cell fraction were extracted separately as previously reported. Mononuclear cells mainly produced C₁₆-PAF, and the content in cell fraction peaked at 30 min as about 10 ng/10⁷ cells. While PAF released in the medium was about 4 ng/10⁷ cells at 30 to 60 min. Acetyltransferase activity in the cells stimulated by PMA increased at 10 min. Addition of p-BPB into the medium completely suppressed PMA-stimulated PAF production by mononuclear cells. While indomethacin and AA-861 did not affect the production. W-7, calmodulin inhibitor, and diltiazem, Ca²⁺ channel blocker, did not show significant reduction of PAF production. In contrast, staurosporine, c-kinase inhibitor, significantly reduced not only PAF production but also increased acetyltransferase activity.
Therefore it seems likely that PMA-induced PAF production links with c-kinase system.

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Human neutrophils showed an increase in cytoplasmic free Ca²⁺ ( [Ca²⁺] i), membrane potential changes (depolarization) and superoxide (O^-₂) release in response to N-formyl-methionyl-leucyl-phenylalanine (FMLP) and the calcium ionophore ionomycin in a dose-dependent manner. When low concentrations of FMLP (10^-10-10^-9M) were used, FMLP induced an increase in [Ca²⁺] i, whereas it induced neither membrane depolarization nor O^-₂ release. When moderate concentrations of ionomycin (10^-10-10^-7M) were employed, ionomycin induced an increase in [Ca²⁺] i and membrane depolarization, whereas it failed to stimulate O^-₂ release. The similar findings were also observed in peripheral blood neutrophils obtained from the colony-stimulating factor producing tumor-bearing nude mice when high concentrations of FMLP (>10^-6M) or ionomycin (10^-10-10^-7M) were employed. These findings suggest that an increase in [Ca²⁺] i by itself is not sufficient to trigger membrane depolarization and O^-₂ release, and that an increase in [Ca²⁺] i with membrane depolarization is not still sufficient to trigger the respiratory burst.

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PMN obtained from synovial fluids of patients with RA was cytotoxic on synovial cultured cells.
Supernatants of synovial lymphocytes of RA patients enhanced the cytotoxic activity of both synovial PMN of RA patients and peripheral PMN of normal subjects on synovial cultured cells.
Supernatants of synovial lymphocytes of RA patients treated with anti IFN-γ antibody did not enhanced the cytotoxic activity of the PMN on synovial cultured cells.
Recombinant IFN-γ enhanced the cytotoxic activity of peripheral PMN of normal subject.

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Because recombinant human interleukin 2 was reported to induce fever on clinical trials, the involvement of interleukin 1 (IL-1) in inducing fever was studied in human blood mononuclear cells and in rabbits.
1. When the mononuclear cells were cultured with 10-3, 000 ng/ml of TGP-3 in the presence of polymyxin B at 37°C for 24 hr, 2-5 ng/10⁶ cells of IL-1β was detected in the culture extract (intracellular and culture supernatant) as determined by a radioimmunoassay. However, the level of IL-1β fluctuated depending on the lot of cell preparations.
2. When the culture extract of the mononuclear cells containing a relatively large amount of IL-1β (over 10 ng/ml) were injected intravenously into the rabbits, the rectal temperature was raised with a peak 50-60 min after the injection; the fever pattern was similar to that typically induced by endogenous pyrogens.
These results suggest that the fever observed on clinical trials of TGP-3 might be due to IL-1β production.

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BSF-2, GM-CSF and IL-1β mRNAs were induced by recombinant IL-1β in human astrocytoma cell line U373MG. The induction of BSF-2 and IL-1β mRNAs by recombinant IL-1β did not require de novo protein synthesis while that of GM-CSF mRNA by recombinant IL-1β required a newly synthesized protein. Therefore it is possible that mRNAs for various cytokines may be regulated entirely by different mechanisms by IL-1 in the same cell line, dexamethasone inhibited the induction of these cytokine mRNAs by recombinant IL-1β in a dose-dependent fashion. However accumulation of BSF-2 and IL-1β mRNAs by recombinant IL-1β was not inhibited by dexamethasone in the presence of cycloheximide. Therefore as yet undiscovered gene product (s) that may be induced by dexamethasone might be involved in the decrease of the level of BSF-2, GM-CSF and IL-1β mRNAs.
These results suggest that the production of these cytokines are positively and negatively controlled by IL-1 and glucocorticoids respectively in astrocytes.

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Corticosteroids which are incorporated in lipid emulsion are easily taken up by reticulo-endothelial system (RES) much more than free corticosteroids. In this study, the immunosuppressive effect of dexamethasone palmitate incorporated in lipid emulsion was compared with that of the free dexamethasone disodium phosphate. It showed that the antibody response in spleen to SRBC and DNP-Ficoll, the proliferative response of spleen cells to mitogens, DTH response to SRBC, ADCC activity of spleen cells and the effect on RES function in mice were strongly suppressed by dexamethasone palmitate incorporated in lipid emulsion when compared with the free corticosteroid. In addition, the effect in delaying mortality by preventing the spontaneous autoimmune disease of MRL/l mice was observed by the treatment with dexamethasone palmitate incorporated in lipid emulsion.
From these results, dexamethasone palmitate incorporated in lipid emulsion is a potent long-acting immunosuppressant and is thought to be of value in the treatment of autoimmune disease such as idiopathic thrombocytopenic purpura (ITP) .

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