Natural and experimental oral infection of nonhuman primates by bovine spongiform encephalopathy agents

Experimental lemurs either were infected orally with the agent of bovine spongiform encephalopathy (BSE) or were maintained as uninfected control animals. Immunohistochemical examination for proteinase-resistant protein (prion protein or PrP) was performed on tissues from two infected but still asymptomatic lemurs, killed 5 months after infection, and from three uninfected control lemurs. Control tissues showed no staining, whereas PrP was detected in the infected animals in tonsil, gastrointestinal tract and associated lymphatic tissues, and spleen. In addition, PrP was detected in ventral and dorsal roots of the cervical spinal cord, and within the spinal cord PrP could be traced in nerve tracts as far as the cerebral cortex. Similar patterns of PrP immunoreactivity were seen in two symptomatic and 18 apparently healthy lemurs in three different French primate centers, all of which had been fed diets supplemented with a beef protein product manufactured by a British company that has since ceased to include beef in its veterinary nutritional products. This study of BSE-infected lemurs early in their incubation period extends previous pathogenesis studies of the distribution of infectivity and PrP in natural and experimental scrapie. The similarity of neuropathology and PrP immunostaining patterns in experimentally infected animals to those observed in both symptomatic and asymptomatic animals in primate centers suggests that BSE contamination of zoo animals may have been more widespread than is generally appreciated.

Immunomodulation of experimental autoimmune encephalomyelitis by oral administration of copolymer 1

The activity of copolymer 1 (Cop 1, Copaxone, glatiramer acetate) in suppressing experimental autoimmune encephalomyelitis (EAE) and in the treatment of multiple sclerosis patients when injected parenterally has been extensively demonstrated. In the present study we addressed the question of whether Cop 1 can induce oral tolerance to EAE similar to myelin basic protein (MBP). We now have demonstrated that oral Cop 1 inhibited EAE induction in both rats and mice. Furthermore, oral Cop 1 was more effective than oral MBP in suppressing EAE in rats. The beneficial effect of oral Cop 1 was found to be associated with specific inhibition of the proliferative and Th1 cytokine secretion responses to MBP of spleen cells from Cop 1-fed mice and rats. In all of these assays, oral Cop 1 was more effective than oral MBP. The tolerance induced by Cop 1 could be adoptively transferred with spleen cells from Cop 1-fed animals. Furthermore, Cop 1-specific T cell lines, which inhibit EAE induction in vivo, could be isolated from the above spleen cells. These T cell lines secrete the anti-inflammatory cytokines IL-10 and transforming growth factor type β, but not IL-4, in response to both Cop 1 and MBP. In conclusion, oral Cop 1 has a beneficial effect on the development of EAE that is associated with down-regulation of T cell immune responses to MBP and is mediated by Th2/3 type regulatory cells. These results suggest that oral administration of Cop 1 may modulate multiple sclerosis as well.

The neuroprotective agent SR 57746A abrogates experimental autoimmune encephalomyelitis and impairs associated blood–brain barrier disruption: Implications for multiple sclerosis treatment

Experimental autoimmune encephalomyelitis (EAE) is a T cell autoimmune disorder that is a widely used animal model for multiple sclerosis (MS) and, as in MS, clinical signs of EAE are associated with blood–brain barrier (BBB) disruption. SR 57746A, a nonpeptide drug without classical immunosuppressive properties, efficiently protected the BBB and impaired intrathecal IgG synthesis (two conventional markers of MS exacerbation) and consequently suppressed EAE clinical signs. This compound inhibited EAE-induced spinal cord mononuclear cell invasion and normalized tumor necrosis factor α and IFN-γ mRNA expression within the spinal cord. These data suggested that pharmacological intervention aimed at inhibiting proinflammatory cytokine expression within the central nervous system provided protection against BBB disruption, the first clinical sign of EAE and probably the key point of acute MS attacks. This finding could lead to the development of a new class of compounds for oral therapy of MS, as a supplement to immunosuppressive agents.

Treatment of experimental autoimmune encephalomyelitis by feeding myelin basic protein conjugated to cholera toxin B subunit.

Oral administration of autoantigens can prevent and partially suppress autoimmune diseases in a number of experimental models, Depending on the dose of antigen fed, this approach appears to involve distinct yet reversible and short-lasting mechanisms (anergy/deletion and suppression) and usually requires repeated feeding of large (suppression) to massive (anergy/deletion) amounts of autoantigens to be effective. Most importantly, this approach is relatively less effective in animals already systemically sensitized to the fed antigen, such as in animals already harboring autoreactive T cells and, thus, presumably also in humans suffering from an autoimmune disorder. We have previously shown that feeding a single dose of minute amounts of antigens conjugated to cholera toxin B subunit (CTB) can effectively suppress delayed-type hypersensitivity reactions in systemically immune animals. We now report that feeding small amounts of myelin basic protein (MBP) conjugated to CTB either before or after disease induction protected rats from experimental autoimmune encephalomyelitis. Such treatment was as effective in suppressing interleukin 2 production and proliferative responses of lymph node cells to MBP as treatment involving repeated feeding with much larger (50- to 100-fold) doses of free MBP. Different from the latter treatment, which led to decreased production of interferon-gamma in lymph nodes, low-dose oral CTB-MBP treatment was associated with increased interferon-gamma production. Most importantly, low-dose oral CTB-MBP treatment greatly reduced the level of leukocyte infiltration into spinal cord tissue compared with treatment with repeated feeding of large doses of MBP. These results suggest that the protection from experimental autoimmune encephalomyelitis achieved by feeding CTB-conjugated myelin autoantigen involves immunomodulating mechanisms that are distinct from those implicated by conventional protocols of oral tolerance induction.

Oral tolerance in myelin basic protein T-cell receptor transgenic mice: suppression of autoimmune encephalomyelitis and dose-dependent induction of regulatory cells.

Orally administered antigens induce a state of immunologic hyporesponsiveness termed oral tolerance. Different mechanisms are involved in mediating oral tolerance depending on the dose fed. Low doses of antigen generate cytokine-secreting regulatory cells, whereas high doses induce anergy or deletion. We used mice transgenic for a T-cell receptor (TCR) derived from an encephalitogenic T-cell clone specific for the acetylated N-terminal peptide of myelin basic protein (MBP) Ac-1-11 plus I-Au to test whether a regulatory T cell could be generated from the same precursor cell as that of an encephalitogenic Th1 cell and whether the induction was dose dependent. The MBP TCR transgenic mice primarily have T cells of a precursor phenotype that produce interleukin 2 (IL-2) with little interferon gamma (IFN-gamma), IL-4, or transforming growth factor beta (TGF-beta). We fed transgenic animals a low-dose (1 mg x 5) or high-dose (25 mg x 1) regimen of mouse MBP and without further immunization spleen cells were tested for cytokine production. Low-dose feeding induced prominent secretion of IL-4, IL-10, and TGF-beta, whereas minimal secretion of these cytokines was observed with high-dose feeding. Little or no change was seen in proliferation or IL-2/IFN-gamma secretion in fed animals irrespective of the dose. To demonstrate in vivo functional activity of the cytokine-secreting cells generated by oral antigen, spleen cells from low-dose-fed animals were adoptively transferred into naive (PLJ x SJL)F1 mice that were then immunized for the development of experimental autoimmune encephalomyelitis (EAE). Marked suppression of EAE was observed when T cells were transferred from MBP-fed transgenic animals but not from animals that were not fed. In contrast to oral tolerization, s.c. immunization of transgenic animals with MBP in complete Freund's adjuvant induced IFN-gamma-secreting Th1 cells in vitro and experimental encephalomyelitis in vivo. Despite the large number of cells reactive to MBP in the transgenic animals, EAE was also suppressed by low-dose feeding of MBP prior to immunization. These results demonstrate that MBP-specific T cells can differentiate in vivo into encephalitogenic or regulatory T cells depending upon the context by which they are exposed to antigen.

ABT-538 is a potent inhibitor of human immunodeficiency virus protease and has high oral bioavailability in humans.

Examination of the structural basis for antiviral activity, oral pharmacokinetics, and hepatic metabolism among a series of symmetry-based inhibitors of the human immunodeficiency virus (HIV) protease led to the discovery of ABT-538, a promising experimental drug for the therapeutic intervention in acquired immunodeficiency syndrome (AIDS). ABT-538 exhibited potent in vitro activity against laboratory and clinical strains of HIV-1 [50% effective concentration (EC50) = 0.022-0.13 microM] and HIV-2 (EC50 = 0.16 microM). Following a single 10-mg/kg oral dose, plasma concentrations in rat, dog, and monkey exceeded the in vitro antiviral EC50 for > 12 h. In human trials, a single 400-mg dose of ABT-538 displayed a prolonged absorption profile and achieved a peak plasma concentration in excess of 5 micrograms/ml. These findings demonstrate that high oral bioavailability can be achieved in humans with peptidomimetic inhibitors of HIV protease.