Learning-induced plasticity of N-methyl-D-aspartate receptors is task and region specific.

Changes in binding of [3H]dizocilpine maleate to N-methyl-D-aspartate-sensitive ion channel receptors were evaluated after learning in order to specify brain regions which might be involved in memory formation. Rats were trained in a five-trial session of 40 min, to discriminate among three odours to obtain food reinforcement. Another group was trained in an eight-arm maze to choose always the same three arms to obtain food reinforcement (nine trials over 150 min). In rats killed 30 min after odour discrimination learning, dizocilpine maleate binding was significantly reduced in hippocampal sub-regions CA3, CA1 and fascia dentata and in frontal cortex. After spatial learning, changes in binding were limited to the amygdala, where a decrease was also observed. These results indicate that functional changes occur in specific brain regions after learning and suggest anatomical loci for further study of synaptic changes at a morphological level, after spatial learning or odour discrimination.

Possible monocytic origin of chondrosarcoma: in vitro transdifferentiation of HLA-DR blood monocyte-like cells from a patient with chondrosarcoma, into neo-fibroblasts and chondrocyte-like cells.

Nodules and multilayered areas composed of fibroblasts and chondrocyte-like cells embedded in an abundant extracellular matrix appeared spontaneously in in vitro culture of mononucleated blood cells taken from a patient with chondrosarcoma. Using specific antibodies it was demonstrated that the neo-fibroblasts which developed in the culture resulted from a direct transdifferentiation of monocytes expressing HLA-DR specificity. The experiment was carried out twice, once before surgery and then two years later. In both cases the spontaneous transdifferentiation of HLA-DR monocytes into neo-fibroblasts was observed. Previously it was shown that normal monocytes were also able to give rise in vitro to neo-fibroblasts. However, the latter are normally rapidly destroyed by cell-cell contact with T-cells. Normal T-cells adhere to normal neo-fibroblasts by which they are finally engulfed. As a result, the neo-fibroblasts lose their fibroblastic shape, no longer adhere to their support and die. Therefore the abnormal proliferation and persistence of neo-fibroblasts in pathological situations such as the present case may result either from an intrinsic defect in monocytes, T-cells or both. The question is whether or not this transdifferentiation process observed in vitro accounts for the development of chondrosarcoma in vivo. The present results suggest that in vivo chondrosarcoma may start in a necrotic zone (resulting for instance from trauma) and attract HLA-DR monocytes, where they accumulate and transdifferentiate into neo-fibroblasts and chondrocyte-like cells. The uncontrolled transdifferentiation of these HLA-DR monocytes resulting from a dysregulation of the immune system is probably linked to the malignant process which may have a retroviral origin. The question is raised regarding the embryologic origin of this special sub-population of blood monocytes in which pluripotential capabilities are retained; its origin may differ from that of the other circulating monocytes.

Immune cell defects affect bone remodelling in osteopetrotic op/op mice.

The aim of the present work was to further characterize immunological defects in osteopetrosis. The op/op mutant mouse is of particular interest since a marrow cavity develops spontaneously in older animals. The interleukin production (IL-1, IL-2, IL-3, IL-4, IL-6), the presence of macrophage differentiation antigens and the evolution of the bone lesions were studied in osteopetrotic and normal mice. Low levels of IL-1, IL-3 and IL-4 were observed at the age of 6 weeks in the op/op mice. However, at 22 weeks of age, the level of IL-1 and IL-4 returned to normal value in these op/op mice whereas the level of IL-3 remained partially decreased at the same age. Furthermore, macrophage expression of MAC-2 antigen, reduced at 12 weeks of age was found to be normal 10 weeks later. These immunological defects and their recovery seems to be concomitant with the healing of the bone lesions.

T-lymphocyte control of HLA-DR blood monocyte differentiation into neo-fibroblasts. Further evidence of pluripotential secreting functions of HLA-DR monocytes, involving not only collagen but also uromodulin, amyloid-beta peptide, alpha-fetoprotein and carcinoembryonic antigen.

Previous studies led us to demonstrate in pathological situations that the fibroblast, not the macrophage, was the terminal maturation step of the HLA-DR monocyte and that the entire process came under T-lymphocyte control. Fibrosis which developed under immunosuppressive treatment (cyclosporin) after organ transplantation is an illustration of these in vitro observations. The present in vitro study was undertaken in order to investigate whether or not this transformation process takes place under physiological conditions and if so, the nature of the T-lymphocyte control. We report that normal HLA-DR monocytes/macrophages are able to secrete type 1 collagen and to differentiate into neo-fibroblasts. However, contrarily to what happened in pathology, only a few neo-fibroblasts developed transiently. The addition of conditioned medium (CM) from activated T-lymphocytes greatly enhanced the transformation process. Counteracting this CM effect, cell-to-cell contact between neo-fibroblasts and T-cells resulted in the loss of fibroblastic shape. The 'end-result' macrophage engulfed numerous lymphocytes giving rise to a multinucleated cell. This giant cell no longer adhered to the slide and died. The question is raised as to whether the process observed in vitro is involved in vivo in tissue repair. We also report that HLA-DR monocytes and the neo-fibroblasts which derive from them are able to secrete, in addition to type 1 collagen, a variety of proteins such as uromodulin, amyloid-beta peptide, alpha-fetoprotein and carcinoembryonic antigen. In cystic fibrosis we previously reported a high level of uromodulin production by HLA-DR monocytes differentiating towards the fibroblastic phenotype. Pathologies characterized by excessive production of either alpha-feto-protein, carcinoembryonic antigen, beta-amyloid protein (Alzheimer's disease) should be investigated, taking into account the involvement of HLA-DR monocytes and their possible uncontrolled differentiation into neo-fibroblasts.

Monocytic origin of fibroblasts: spontaneous transformation of blood monocytes into neo-fibroblastic structures in osteomyelosclerosis and Engelmann's disease.

We describe here two pathological situations, osteomyelosclerosis and Engelmann's disease, in which HLA-DR blood monocytes modulate to the fibroblastic class, in long-term culture. Monocytes/macrophages were identified by immunofluorescence, using monoclonal antibodies against surface markers (Leu M3, CD 68, and HLA-DR) and the neo-fibroblasts by electron microscopy and immunofluorescence using monoclonal antibodies against a cytoplasmic enzyme specifically involved in the synthesis of collagen (5B5). Macrophages makers were found on the neo-fibroblasts, whereas HLA-DR macrophages expressed the cytoplasmic marker 5B5. Since osteoblasts are classically derived from fibroblasts, the significance of the in vitro differentiation of monocytes/macrophages into fibroblasts to the in vivo mechanism leading to excessive osteoblastic proliferation in both osteomyelosclerosis and Engelmann's disease, is discussed. The possible involvement of this pathway leading from monocytes to fibroblasts and osteoblasts in the normal process of bone modeling and remodeling in questioned.

Cystic fibrosis: production of high levels of uromodulin-like protein by HLA-DR blood monocytes differentiating towards a fibroblastic phenotype.

We report here the spontaneous in vitro transformation of blood monocytes into fibroblasts, in a patient suffering from cystic fibrosis (CF). The blood monocytes with this capacity express HLA-DR specificity. Monocytes were identified by non-specific esterase activity and by immunofluorescence using monoclonal antibodies against monocytes/macrophages antigens. Neo-fibroblasts were identified by electron microscopy and immunofluorescence using monoclonal antibodies against a cytoplasmic enzyme specifically involved in the synthesis of collagen. The secretion of collagen was evidenced using antibodies against type I collagen. Both monocytes/macrophages and neo-fibroblasts express the monocytic and the fibroblastic markers and synthesize type I collagen. This transformation observed in vitro might mimick the process of fibrosis development which takes place in vivo, particularly in pancreatic acini, lungs and intestine of patients with CF. Interestingly, the whole process in vitro is inhibited when T lymphocytes are properly stimulated by IL2. In addition, both monocytes and neo-fibroblasts secrete high quantities of uromodulin-like glycoprotein. The significance of this finding is discussed in relation to the thick mucus secretion which characterizes the disease. In addition, from a fundamental point of view, it confirmed in a large series of patients that this observation may have significant implications, since CF mutation impairs the gene coding for cAMP-regulated Cl- channel and that it has been proposed that uromodulin might be implicated in Cl- transport. Therefore the question of the relationships between uromodulin and the cAMP-regulated Cl- channel arises.

Dichloromethylene diphosphonate (Cl2MDP) reduces natural killer (NK) cell activity in mice.

Daily administration of dichloromethylene diphosphonate (Cl2MDP) to (C57BL/6 X DBA/2) F1 hybrid mice, from two days of age (10 mg of P/kg body weight), resulted in a marked impairment of natural killer (NK) activity of spleen cells against YAC-1 lymphoma cells. The suppressive effect increased with the duration of the treatment. Cessation of the treatment led to a rapid recovery (in 2 weeks) of NK activity while the osteopetrotic bone lesions persisted. Thus, the loss of natural killing cannot be explained by the simple reduction of bone marrow volume secondary to Cl2MDP-induced osteopetrosis. However, as NK cells are considered to be dependent on the bone marrow because they cannot be sustained by extramedullary production, a direct effect of Cl2MDP on the generation of NK cell precursors by the bone marrow was not excluded. Cl2MDP was not directly toxic to the fully differentiated splenic NK cells, since the addition of Cl2MDP to the in vitro assay (10(-5)-10 micrograms/ml) did not reduce cytotoxicity. These studies suggest that impairment of NK activity during Cl2MDP treatment may have clinical toxicologic implications since NK cells have been suggested to play an important role in natural host defenses against infection and neoplasia.

A baby with Di George syndrome treated with bovine thymic extracts: a 3.5 yr analysis of variations in the distribution of lymphocytes characterized by three tests of cell mediated immunity and electrophoretic mobility.

This report concerns a baby with the features of Di George syndrome. Bovine thymic extracts prepared in this laboratory were used to treat the baby between the ages of 1 and 18 months. A favourable evolution of the illness was noticed, suggesting the diagnosis of Di George syndrome in its partial form and/or a favourable response to the treatment with thymic extracts. The number of E-rosette forming T-lymphocytes in blood remained low during the 3.5 yr of the observation. The in vitro response of peripheral blood lymphocytes to phytohemagglutinin and to allogenic cells slowly increased during this period of time. Surprisingly, no change in the proportions of lymphocytes of high electrophoretic mobility and low electrophoretic mobility was observed, in contrast to the gradual change usually observed in normal individual age-matched controls.

(Dichloromethylene)diphosphonate-induced impairment of T-lymphocyte function.

The daily subcutaneous administration of (dichloromethylene)diphosphonate (clodronate) to 3-day-old normal inbred Wistar-Furth rats for 30 days produces osteopetrotic bone lesions resembling those of the osteopetrotic mutants. Furthermore, tooth eruption is prevented, growth slows down, and signs of runt disease appear. The weight of the thymus is decreased, and T cells from the thymus and spleen respond weakly to mitogens. These thymic disorders associated with defective bone resorption are very similar to those previously reported in the osteopetrotic mutant op rat and support the hypothesis of a link between the thymus and normal bone modeling and remodeling.

Lack of a T-cell dependent subpopulation of macrophages in (dichloromethylene) diphosphonate-treated mice.

In Cl2MDP-osteopetrotic mice, one subpopulation of thioglycollate-induced peritoneal exudate macrophages (M phi) is missing. This subpopulation is precisely the one whose differentiation is known to be dependent on T-lymphocytes, as it is also missing in the athymic nu/nu mice. Cl2MDP-induced osteopetrosis being partially attributable to deficient osteoclastic bone resorption, raises the possibility that this missing M phi subpopulation might represent the precursors of osteoclasts. It is suggested from this work that the interplays between T-cells and M phi, so well known in immunity and inflammation, may also be relevant to osteoclastic differentiation and therefore, to bone remodeling.

Gene dependent differences in malignant osteopetrosis as evidenced by cellular induction of the disease.

Osteopetrosis was induced in lethally irradiated normal rats by cell infusion prepared from spleens of the osteopetrotic (op) mutant littermates. However, similar attempts to induce osteopetrosis in another strain of osteopetrotic rats, namely the "toothless" (tl) rats, were unsuccessful. This discrepancy between op and tl rats with regard to the transmission of the disease to normal littermates, parallels the response of the respective mutants to treatment by normal bone marrow cells: the op rat is cured, not the tl rat. The present findings confirm the cellular origin of osteopetrosis in the op rat, whereas the origin of the defect in the tl mutant remains obscure.

Resistance to adjuvant arthritis induced by a genetic mutation, osteopetrosis.

Adjuvant arthritis stands as the closest model to human rheumatoid arthritis. A genetic mutation (op) recognized to provoke osteopetrosis in rats, completely inhibits their ability to develop adjuvant arthritis. Osteopetrosis in the op mutant is linked to deficiencies in T-lymphocytes and macrophages functions. Therefore this animal model may be helpful for a better understanding of the immunoregulation impairment involved in adjuvant arthritis.

Osteopetro-rickets: a new congenital bone disorder.

Two lethal mutations have been described in the rat: "osteopetrosis" (op) and "toothless" (tl). The op mutant can be cured by normal bone marrow infusion, while the tl mutant cannot. We report here additional data with regard to the tl mutant. The bone disease of the tl rat as in the op rat is associated with a precocious thymic atrophy, but bone lesions are quite different. In addition to classical osteopetrosis, the tl rat displays several features of rickets: broadening of the extremities of long bones, thickening of the epiphyseal plates, presence of osteoid areas. In addition, the persistence of embryonic characters, evidenced by high levels of alpha-fetoprotein, suggests that the developmental defect of bone is part of a more general process.

[Thymus and bones]. / Thymus et os.

Rat congenital osteopetrosis and cyclophosphamide (an immunosuppressive drug) induced osteocondensation are useful experimental models for the understanding of the relationships which seem to exist between thymus and bone. The high levels of seric alphafetoprotein found in the osteopetrotic tl rat raise the question of the persistance of embryonic characters in congenital osteopetrosis.