Patricia A. Gonnella

B cell-deficient (mu MT) mice have alterations in the cytokine microenvironment of the gut-associated lymphoid tissue (GALT) and a defect in the low dose mechanism of oral tolerance.

Peripheral immune tolerance following i.v. administration of Ag has been shown to occur in the absence of B cells. Because different mechanisms have been identified for i.v. vs low dose oral tolerance and B cells are a predominant component of the gut-associated lymphoid tissue (GALT) they may play a role in tolerance induction following oral Ag. To examine the role of B cells in oral tolerance we fed low doses of OVA or myelin oligodendrocyte glycoprotein to B cell-deficient (μMT) and wild-type C57BL/6 mice. Results showed that the GALT of naive wild-type and μMT mice was characterized by major differences in the cytokine microenvironment. Feeding low doses of 0.5 mg OVA or 250 μg myelin oligodendrocyte glycoprotein resulted in up-regulation of IL-4, IL-10, and TGF-β in the GALT of wild-type but not μMT mice. Upon stimulation of popliteal node cells, in vitro induction of regulatory cytokines TGF-β and IL-10 was observed in wild-type but not μMT mice. Greater protection against experimental autoimmune encephalomyelitis was found in wild-type mice. Oral tolerance in μMT and wild-type mice was found to proceed by different mechanisms. Anergy was observed from 0.5 mg to 250 ng in μMT mice but not in wild-type mice. Increased Ag was detected in the lymph of μMT mice. No cytokine-mediated suppression was found following lower doses from 100 ng to 500 pg in either group. These results demonstrate the importance of the B cell for the induction of cytokine-mediated suppression associated with low doses of Ag.

Mechanisms of recovery from experimental autoimmune encephalomyelitis: T cell deletion and immune deviation in myelin basic protein T cell receptor transgenic mice.

Experimental autoimmune encephalomyelitis (EAE) is a Th1-type cell-mediated autoimmune disease directed against central nervous system (CNS) myelin antigens such as myelin basic protein (MBP). EaE is usually characterized by spontaneous remission of clinical disease and immune pathology despite the persistence of self myelin antigens in the central nervous system. Following induction of an acute episode of EAE, spontaneous remission also occurs in MBP T cell receptor (TCR) transgenic mice even through most T cells express a TCT specific for MBP. To investigate the mechanisms of recovery associated with EAE, we examined the behavior of MBP-specific T cells in the MBP TCR transgenic mouse model during disease progression and recovery. We found that recovery from EAE was associated with three major immunologic changes: (1) deletion of encephalitogenic T cells in the brain; (2) deviation of MBP-specific transgenic (Tg+) T cells both in the periphery and in the central nervous system from INF- gamma secretin Th1 type cells to cells that secrete IL-4, IL-10, and TGF- beta ; and (3) deletion of Tg+ T cells in the thymus through apoptosis. Thus spontaneous recovery from a classic Th1 type organ specific autoimmune disease is associated with two mechanisms of immune tolerance, deletion of autoreactive cells and immune deviation of autoreactive cells to a non-pathogenic phenotype.

Effect of oral beta interferon on subsequent immune responsiveness.

Oral administration of myelin antigens reduces the incidence and severity of EAE in rat and mouse models and decreases the frequency of MBP-reactive cells and the frequency of attacks in some patients with multiple sclerosis. Low-dose oral tolerance has been shown to be mediated by Th2-type regulatory cells that secrete TGFbeta and IL-4/IL-10. Adjuvants and cytokines may modulate oral tolerance. The addition of betaIFN to the experimental therapy regimen, either orally or by intraperitoneal injection, has been shown to enhance the suppressive effects of oral myelin antigens when either are fed the suboptimal dosing regimen to suppress EAE. The current studies were conducted to elucidate the mechanism of the observed in vivo synergy of betaIFN and antigen feeding. Analysis of the in vitro proliferative response and cytokine production by lymphocytes from fed animals in response to specific antigen in culture shows that the synergistic effect may be related to both independent suppression of the immune response by oral betaIFN and enhanced production of TGFbeta and IL-4/IL-10. There was an unexpected increase in the production of gammaIFN by lymphocytes in vitro after three doses of oral betaIFN in vivo. These observations have important implications for the use of cytokines to modulate oral tolerance.

Induction of Low Dose Oral Tolerance in Monocyte Chemoattractant Protein-1- and CCR2-Deficient Mice

The chemokine monocyte chemoattractant protein-1 (MCP-1) and its receptor CCR2 have been shown to play an important role in the migration and trafficking of macrophages and Th1 effector cells in experimental autoimmune encephalomyelitis. Also, MCP-1 has been reported to regulate oral tolerance induction by inhibition of Th1 cell-related cytokines and by the ability of Abs to MCP-1 to inhibit oral tolerance. This study demonstrates that neither MCP-1 nor its receptor CCR2 is required for the induction of oral tolerance. Mice deletional for either MCP-1 or CCR2 had suppressed cell-proliferative and Th1 responses following oral administration and immunization with myelin oligodendrocyte glycoprotein (MOG35–55). TGF-β was up-regulated in fed and immunized deletional mice, while IL-4 was absent from deletional mice, but up-regulated in controls. Decreased experimental autoimmune encephalomyelitis severity was found in MOG35–55-fed MCP-1 deletional mice, indicating induction of oral tolerance. These results demonstrate that MCP-1 is not required for induction of oral tolerance and that MCP-1 and CCR2 are essential for up-regulation of IL-4 in tolerized mice.