Studies on the maturation of thymus stem cells. The effects of catecholamines, histamine and peptide hormones on the expression of T cell alloantigens

Early events in T lymphocyte genesis in the fetal thymus

There is considerable uncertainty about the nature and level of maturation of the stem cells which colonize the thymus. Arguments are presented here which raise doubts about the claims that these cells have undergone substantial maturation along the T-lineage pathway prior to migration to the thymus. Instead, emphasis is placed on the role of thymic stromal cells in T-lymphocyte maturation. The heterogeneous nature of these cells is well established, but progress is described in analyzing the various cell types and their embryological origins. In particular, the expression of the major histocompatibility complex (MHC) antigens on thymic stromal cells might be relevant to the understanding of restriction and tolerance. The early phases of thymus lymphocyte differentiation are described; but no clear account of the generation of T-cell subsets from immature cells can, as yet, be offered.

The effect of histamine on the development of adjuvant arthritis in the rat

Histamine, injected subcutaneously (0.3-10 mg/kg), produced a dose-related inhibition of the primary and secondary inflammation, and the development of the secondary lesions of rat adjuvant arthritis. Histamine was effective when given for short periods around the time of adjuvant administration and could also delay and possibly reverse an established arthritic response. The histamine H1-agonist, 2-(2-pyridyl)-ethylamine, inhibited rat adjuvant arthritis, whereas the histamine H2-agonists, impromidine and dimaprit, failed to affect the response. Metiamide, a histamine H2-antagonist (5 mg/kg), reduced the inflammation in the uninjected hind-paw and the development of secondary lesions. Histamine may have two effects on rat adjuvant arthritis, inhibiting the response via stimulation of H1-receptors and augmenting the response via stimulation of H2-receptors. Since histamine is known to bind to and to alter the reactivity of cells which are involved in the regulation of immune responsiveness, it is suggested that interactions with these cells are responsible for the observed effects of histamine.

Expression of Thy-1 antigen is not limited to T cells in cultures of mouse hemopoietic cells

Large numbers of Thy-1-positive cells were observed in cultures of bone marrow cells that had been depleted of T cells and grown for 3 to 4 days in the presence of medium conditioned by concanavalin A-activated spleen cells. Cells bearing levels of Thy-1 comparable with those on the bulk of thymocytes were isolated by using the fluorescence-activated cell sorter. Although many were large blasts, the Thy-1-positive cells failed to grow in response to T-cell growth factor and concanavalin A; about one-third, however, proliferated in the presence of factors stimulating hemopoietic progenitor cells. Furthermore, the Thy-1-positive population included cells capable of forming large colonies of macrophages and granulocytes in agar and cells forming splenic colonies in lethally irradiated mice. The appearance of the Thy-1-positive cells did not correlate with the presence of either T-cell growth factor or T-cell-derived granulocyte/macrophage colony-stimulating factor. These findings indicate that Thy-1 can occur on various murine hemopoietic stem and progenitor cells and myeloid cells; Thy-1 can no longer be regarded as an unambiguous marker of commitment to the T-cell lineage.

Noradrenergic sympathetic innervation of lymphoid tissue in the rabbit appendix: further evidence for a link between the nervous and immune systems

The rabbit appendix, a region of gut with well organized zones of lymphoid tissue, was examined with the glyoxylic acid histofluorescence technique for the localization of noradrenergic fibers, with high performance liquid chromatography with electrochemical detection (LCEC) for the quantitation of norepinephrine and serotonin, with Bielshowski and Giemsa stains for additional information about neural supply, and with acetylcholinesterase histochemistry for the localization of this hydrolytic enzyme. Fluorescent plexuses entered the serosal surface of the appendix associated with blood vessels, traveled longitudinally inside the muscularis interna, mainly in association with blood vessels but adjacent to enteric smooth muscle, and branched into long, linear, varicose plexuses that ran inward in a radial orientation towards the lumen in the internodular septa. As these fibers approached the interdomal regions near the epithelial surface, they passed through thymus-dependent cell zones, and arborized extensively throughout the interdomal region. A high density of varicosities was found in the subepithelial region where immunoglobulin-secreting plasma cells are found. These varicosities were sparse at 21 days of age, but were increased in number at 42 days of age. They were even further increased in number and density in adults. These fibers were further identified with a Bielshowski silver stain, and also demonstrated acetylcholinesterase activity. The noradrenergic varicosities in the interdomal regions of the adult rabbit appendix were closely associated with numerous yellow fluorescent cells of 25-40 microns diameter, which sometimes demonstrated fine varicose processes. The adult rabbit appendix contained a moderate concentration of norepinephrine (163.0 +/- 22.9 ng/g wet weight) and a very high concentration of serotonin (3981 +/- 283 ng/g wet weight). Levels in neonates were considerably lower, suggesting that the yellow fluorescent cells may contain serotonin. Acetylcholinesterase was associated with neural fibers and with non-neural regions of the lymph nodules and the domes, perhaps playing a protective role for these regions of the cellular immune system. The rabbit appendix is a well organized region of lymphoid tissue with specific zones of noradrenergic innervation and possible "paraneuronal" activity, with a readily accessible lumen for the isolation and collections of secretions. We propose this model as an excellent structure for further exploration of interactions between the nervous and immune systems.

Sympathetic innervation of murine thymus and spleen: a comparative histofluorescence study

Fluorescence microscopy of thymus and spleen from four strains of mice (C3H and ICR controls, AKR spontaneously leukemic and NZB autoimmune) revealed varicose noradrenergic (NE) fibers in perivascular and parenchymal regions of both organs. Thymic innervation was largely perivascular, but isolated islands and strings of free NE fibers were noted among thymic parenchymal cells. A morphological proximity between NE fibers in the thymus and mast cells was noted in all strains studied, but was exceptionally prominent in the NZB thymus. Perivascular plexuses within the splenic white pulp sent single NE fibers between the surrounding lymphocytes. Catecholamines and histamine have been shown to modulate lymphocyte development and activity in vitro. The present study provides morphological evidence that both NE and histamine are available to lymphocytes in thymus and spleen, and thus provides morphological evidence for neural modulation of immune activity in vivo.

Sympathetic innervation of murine thymus and spleen: evidence for a functional link between the nervous and immune systems

Sympathetic innervation was demonstrated in both perivascular and parenchymal regions of murine thymus and spleen. Catecholamine varicosities were associated with mast cells in these areas. The antibody response to sheep red blood cells of 7 week old mice that had been sympathectomized with six-hydroxydopamine (6OHDA) at birth was significantly elevated compared with saline treated controls. Alpha-methyl tyrosine (alpha-MT) and 6OHDA treatment of mice, producing a more complete sympathectomy, showed a significantly enhanced anti-SRBC response with respect to mice treated with alpha-MT or 6OHDA alone. Catecholamine levels in thymus, spleen, and adrenals of both experimental and control mice were measured using liquid chromatography with electrochemical detection (LCEC). The present study suggests that the sympathetic nervous system has a functional role in modulating the humoral immune response in vivo.

Effect of histamine agonists and antagonists on the production of murine reaginic antibodies

At least wo histamine receptors have been pharmacologically defined. Using the appropriate agonists and antagonists, the possible involvement of these receptor types in the production of reaginic antibodies in the rodent was investigated. After injecting mice with dinitrophenyl-ovalbumin (DNP-OA), maximal serum reaginic titers occurred on day 11 as measured by heterologous passive cutaneous anaphylaxis. If the mice were dosed daily (i.p.) with the H1 agonist, 2-methylhistamine, or the H2 antagonist, metiamide, the titers of reaginic antibodies on day 11 were significantly higher than the controls. The titers were significantly lower than the controls if an H2 agonist (4-methylhistamine, dimaprit, or impromidine) or if the H1 antagonist, pyrilamine, was administered daily. None of these agents significantly affected total serum IgG titers as measured by ELISA. However, if the mice were injected with DNP-OA on day 0, then dosed daily with metiamide, pyrilamine, or 4 methylhistamine beginning on day 32, the titers of reaginic antibodies elicited by a second injection of DNP-OA given on day 36 were not significantly different from the titers of the non-drug treated mice. Thus, under these conditions, with these agents, the results suggest that histamine receptors may be involved in modulating the production of reaginic antibodies during a primary immunological response, H1 receptor agonists enhanced, while H2 receptor agonists suppressed the responses, and the reverse effect was observed with the appropriate antagonists. However, histamine receptors appear not to be measurably involved in the development of the secondary reaginic response.

Histamine 2-receptor-mediated immunomodulation in the mouse. II. Immunomodulation by the H2 antagonist metiamide

Modulation of delayed hypersensitivity and antibody formation to sheep red cells by metiamide were studied in the mouse system. Depending on the time and dose of antigen and metiamide administration suppression or enhancement of the delayed hypersensitivity response was observed. The effects in this system did not differ from those reported for the H2 agonist tolazoline, which were most probably mediated by suppressor cells. As far as the humoral response was concerned metiamide tended to stimulate the IgM response. Optimal stimulation was reached if 50 mg metiamide/kg was administered 3 days before immunization with 2 x 10(8) SRBC. Under all conditions tested the IgG response was unaffected. These results suggest antagonistic effects of metiamide for tolazoline and adduce further evidence for the presence of H2 receptors on B cells. The IgM production per plasmacell was enhanced suggesting different H2 receptors to be involved in differentiative and proliferative B cell responses. The possible consequences of H2 antagonist application in human therapy are discussed.

The regulation of prostaglandin E1 formation: a candidate for one of the fundamental mechanisms involved in the actions of vitamin C

Vitamin C stimulates the formation of PGE1 in human platelets. The effect occurs over the physiologically relevant range of concentrations. PGE1 is required for T lymphocyte function and plays a major part in the regulation of immune responses. PGE1 is also important in the regulation of collagen and ground substance metabolism, in cholesterol metabolism and in regulation of responsiveness to insulin. It is proposed that defective formation of PGE1 could account for many of the features of scurvy and for many of the reported therapeutic effects of vitamin C. If correct, vitamin C will be of value only in conjunction with an adequate supply of dihomogammalinolenic acid, the precursor of PGE1. Essential fatty acids, pyridoxine and zinc are all required to achieve this.

The pineal and regulation of fibrosis: pinealectomy as a model of primary biliary cirrhosis: roles of melatonin and prostaglandins in fibrosis and regulation of T lymphocytes

Pinealectomy leads to increased formation of fibrous tissue in the abdominal cavity, increased skin pigmentation and elevated cholesterol and alkaline phosphatase levels. It also leads to reduced formation and/or action of prostaglandin (PG) E1 and thromboxane (TX) A2. PGE1 plays an important role in enhancing function of T suppressor lymphocytes which control overactive antibody-producing B lymphocytes. In primary biliary cirrhosis there are increased skin pigmentation, hepatic fibrosis, elevated cholesterol and alkaline phosphatase levels, defective T lymphocytes and hyperactive B lymphocytes. Primary biliary cirrhosis may be a pineal deficiency disease. Serotonin is important in the pineal and the serotonin antagonist methysergide may cause retroperitoneal fibrosis by interfering with pineal function. There is a good deal of other evidence which suggests that melatonin PGE1 and TXA2 are important in the regulation of fibrosis in other situations such as "collagen" diseases, lithium-induced fibrosis and cardiomyopathies. This suggests that enhancement of formation of PGE1 and TXA2 may be of value in diseases associated with excess fibrosis and defective T suppressor cell function. PGE1 levels may be raised by zinc, penicillin, penicillamine and essential fatty acids. TXA2 levels may be raised by low dose colchicine. These new approaches to treatment may prove safer and more effective than existing ones. They may be of value in disorders such as cardiomyopathy, Hodgkin's disease and other lymphomas, multiple sclerosis, Crohn's disease, atopy and other diseases in which defective T cell function is suspected.

Multiple sclerosis: the rational basis for treatment with colchicine and evening primrose oil

Multiple sclerosis (MS) is a disease with no known treatment. In view of this and of its distressing nature patients are attracted by any new concepts. As a reaction to this neurologists are sometimes excessively sceptical and fail to consider new approaches seriously. Recent attempts have been made to treat multiple sclerosis with polyunsaturated fatty acids and with colchicine. This approach is not arbitrary and is firmly grounded in fundamental basic scientific concepts. In patients with multiple sclerosis there is evidence of both an abnormality in essential fatty acid metabolism and an abnormality in lymphocyte function. It is now apparent that the fatty acid abnormality may cause the lymphocyte abnormality and that both may be improved by dietary manipulation. There is also evidence that the demyelination may be associated with recurrent inflammatory episodes and with entry of calcium into the cytoplasm. In vitro colchicine has been shown to have actions compatible with regulation of cytoplasmic calcium and in two diseases characterised by intermittent inflammatory episodes (Behçets syndrome and familial Mediterranean fever) it has been found to prevent or to reduce the severity of such episodes. Preliminary results suggest that combined therapy with evening primrose oil and colchicine may be of considerable value.

Thymic changes in muscular dystrophy and evidence for an abnormality related to prostaglandin synthesis or action

In Bar Harbor 129 dystrophic mice, thymic development is abnormal. Before weaning, the thymus is slightly smaller than in phenotypically normal littermates; after weaning, however, the lymphoid elements undergo rapid atrophy. The epithelial elements, in contrast, display hyperlasia. Thymectomy has no influence on the course of the disease, and it is possible that the thymic changes are a reflection of a fundamental metabolic abnormality. Thymic lymphoid tissue development seems to require normal levels of PGE1. Levels that are either too high or too low both result in abnormalities. We have investigated the effects of PGE1 in smooth muscle and have demonstrated that while some PGE1 is required for both calcium release and calcium removal, high levels of PGE1 block both processes. We propose that the muscular dystrophies are related to defects in PG synthesis and action. Myotonic dystrophy may be due to PGE11 excess, whereas Duchenne dystrophy may in part be due to PGE1 deficiency.