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Multiple sclerosis (MS) is a complex human autoimmune-type disease with a predominantly unknown etiology. Immunologic destruction of myelin basic protein (MBP) throughout the nervous system is the major pathology of multiple sclerosis. This review will attempt to update new information about basic mechanisms and therapeutic management of the disease. The significance of the structure of MBP is discussed with respect to the contribution of such structures to the disease process. A number of MBP peptides that serve as the immunodominant antigens in MS patients have been identified. These peptides have been studied in animal models for their antigenic characteristics and ability to induce disease. Evidence for genetic contributions is reviewed with multigenerational twin studies providing the best evidence for susceptible haplotypes. The role of microorganisms/viruses and environmental agents are discussed as potential etiological factors but are now thought to be of minor importance to the primary causal development of the disease. Of major consideration are immunological mechanisms that contribute to the development of autoimmunity. In particular, antigen expression, cytokine and leukocyte interactions, and regulatory T-cells are discussed. Particular attention is given to regulatory T-cells (Treg), which help balance/modulate other T-cells such as Th1 and Th2 cells, and how such Treg regulate autoimmunity is addressed. The importance of the role of Tregs is exemplified by the demonstration that administration of oral antigens can induce specific Tregs that counteract experimental autoimmune encephalomyelitis in animal models. The significance of animal studies to human multiple sclerosis is discussed. A potential role for natural antibodies and innate immune mechanisms to help provide resistance to disease development is also reviewed. Finally, a variety of therapeutic agents that have been and continue to be utilized for multiple sclerosis is reviewed. Trials with oral antigens, such as glatirmer acetate (copolymer 1) especially in combination with interferon-beta, have shown promise. Antibody therapy and bone marrow transplantation are also briefly discussed.

The aspartate-99 of secreted phospholipase A2 (PLA2) has been proposed to be critical for the catalytic mechanism and interfacial activation of PLA2. Aspartate-99 connects the catalytic machinery (including the catalytic diad, the putative catalytic waters W5 and W6, and the calcium cofactor) to the hydrogen-bonding network. The latter involves Y52, Y73, the structural water, and the N-terminal region putatively required for the interfacial activation. A triple mutant of bovine pancreatic PLA2 with substitutions aspartate plus adjacent tyrosine residues (Y52,73F/D99N) was constructed, its X-ray structure was determined, and kinetic characteristics were analyzed. The kinetic properties of the D99N mutant constructed previously were also further analyzed. The X-ray structure of the Y52,73F/D99N mutant indicated a substantial disruption of the hydrogen-bonding network including the loss of the structural water similar to that seen in the structure of the D99N mutant published previously [Kumar, A., Sekharudu, Y. C., Ramakrishnan, B., Dupureur, C. M., Zhu, H., Tsai, M.-D., & Sundaralingam, M. (1994) Protein Sci. 3, 2082-2088]. Kinetic analysis demonstrated that these mutants possessed considerable catalytic activity with a k(cat) value of about 5% compared to WT. The values of the interfacial Michaelis constant were also little perturbed (ca. 4-fold lower for D99N and marginally higher for Y52,73F/D99N). The results taken together suggest that the hydrogen-bonding network is not critically important for interfacial activation. Instead, it is the chemical step that is perturbed, though only modestly, in the mutants.

The effects of selected heme analogues on heme oxygenase activity in tissues and on human and rabbit bone marrow hematopoietic colony growth were examined. Zinc protoporphyrin (ZnPP) and zinc mesoporphyrin (ZnMP), at concentrations ranging between 1 and 20 M, produced significant inhibition of human and rabbit bone marrow erythroid (CFU-E, BFU-E) and myeloid (CFU-GM) colony growth. The growth inhibition produced by ZnPP or ZnMP was not overcome with exposure of cultures to elevated levels of the growth factors erythropoietin and granulocytemacrophage colony stimulating factor. In contrast, tin protoporphyrin and tin mesoporphyrin did not display any significant bone marrow toxicity when used at similar concentrations. In other studies, differential effects of tin mesoporphyrin and ZnMP administered intravenously on kidney heme oxygenase were demonstrated. Chromium mesoporphyrin administered intravenously proved lethal to animals. These results indicate that exposure of bone marrow to ZnPP and ZnMP can be deleterious to hematopoietic cells and raise the possibility that ZnPP, which is endogenously formed and found in high concentration in red blood cells in lead-poisoned children, may itself participate in the bone marrow toxicity produced by this metal.Hematopoietic cell growth and differentiation within the bone marrow microenvironment are dependent on a complex interplay of cells, cytokines, growth factors, and heme oxygenase (HO) activity, with the latter enzyme playing a major regulatory role in this system. Heme, a potent inducer of HO expression has been shown to have modulatory effects on hematopoiesis (1). A comprehensive study comparing the effects on hematopoietic cells of synthetic heme analogues, which inhibit HO activity has, not previously been undertaken. Information from this type of study is of special importance because of the clinical potential (2-8) of certain of these compounds.In this study we compared the effects of tin and zinc porphyrins on hematopoietic cell growth and colony formation in animal and human bone marrow cultures. Such cell systems are especially vulnerable to the nature of their microenvironment and thus can provide sensitive indices of the deleterious potential of various chemical agents.The results of this study indicate that zinc porphyrins are toxic to both myeloid and erythroid cell growth even at low concentrations. In contrast, tin porphyrins, even at high concentrations, displayed no toxic effects on hematopoiesis. In other experiments tin and zinc porphyrins were shown to have differing effects on renal HO activity when administered intravenously (i.v.). Chromium mesoporphyrin (CrMP) proved lethal to animals when administered by the iv route.These findings provide additional examples of the differential effects of HO inhibitors on cell functions based on their central metal atom and on their route of administration. The inhibitory actions of zinc porphyrins on bone marrow cell growth represent newly identified deleterious properties of these metalloporphyr...

A B S T R A C T In the plasma clot culture system, both normal and polycythemia vera (PV) bone marrow cells respond to erythropoietin (Ep), giving rise to large numbers of colonies of erythroid cells. In PV, but not in normal individuals, the marrow produced endogenous erythroid colonies (EEC) in the absence of exogenous Ep. The number of EEC formed varied from patient to patient comprising anywhere from 6 to 29% of the total number of colonies formed in the presence of Ep. Exposure, before use in culture, of fetal calf serum and citrated bovine plasma to the gammaglobulin fraction of rabbit anti-Ep serum followed by treatment with goat anti-rabbit gamma-globulin resulted in a significant decrease in EEC formation. Addition of anti-Ep directly to the culture medium produced similar results. In addition, the production of EEC in response to added Ep was inhibited in the presence of anti-Ep. Addition of very small doses of highly purified Ep to anti-Ep-treated cultures resulted in the reappearance of a significant number of EEC. These results suggest that EEC formation in PV may be due to a population of erythroid-committed precursors that are abnormally sensitive to small concentrations of Ep which may be present in fetal calf serum and citrated plasma. Although the mechanism of formation of these cells is not known, it appears that the final steps in the formation of red cells derived from this clone of precursors is subject to the usual Ep control.

To explore the possible role of cell-mediated suppression of erythropoiesis in acquired aplastic anemia, we studied the effect of peripheral blood lymphocytes from seven patients with aplastic anemia on erythroid-colony formation by normal human bone marrow in an in vitro plasma clot-culture system. Varying numbers of peripheral blood lymphocytes (0.5 to 6 X 10(5) cells) were cocultured with 6 X 10(5) normal bone-marrow cells in the presence of 2 IU of erythropoietin for seven days. Peripheral blood lymphocytes from five of the seven patients with aplastic anemia caused a 79 to 94 per cent reduction of erythroid-colony formation. Thus, at a peripheral blood lymphocyte concentration of 2 X 10(5) cells, the numbers of erythroid colonies formed (control vs. experimental) were 374 +/- 16 (S.E.M.) vs. 22 +/- 6, 48 +/- 4, 50 +/- 16, 80 +/- 4 and 27 +/- 3. These results suggest that some patients with aplastic anemia possess a population of lymphocytes capable of suppressing in vitro erythropoiesis.

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Peripheral blood lymphocytes from six patients with congenital hypoplastic anemia suppressed erythroid cell formation by normal human bone marrow cells in response to erythropoietin in vitro. The results suggest that the anemia in these children has an immunologic basis.