Intranasal administration of recombinant mouse interleukin-12 increases inflammation and demyelination in chronic experimental autoimmune neuritis in Lewis rats

Pathogenesis of Guillain–Barré syndrome

Guillain-Barre syndrome is a postinfectious disorder caused by an aberrant immune response to an infectious pathogen, resulting in an autoimmune disease. As with other autoimmune diseases of infectious nature, the intricate balance of the numerous factors involved in the immune response may determine the outcome of the interaction between the microbe and host. Recent studies focusing on the role of cytokines and its network of related mediators and receptors suggest that any imbalance may make a significant contribution to the outcome of the infectious disease process. Better understanding of the pathogenesis of Guillain-Barre syndrome may lead to the discovery of newer therapeutics and may also serve as a model for studying other autoimmune diseases.

Proinflammatory cytokines in serum and cerebrospinal fluid of CIDP patients

INTRODUCTION

Little is known about the role of cytokines in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Interleukin (IL)-12 and IL-15 are the major growth and differentiation factors for Th-1 cells and IL-17 is a marker of Th-17 cell expansion and activation, a high proinflammatory new subset of T cells that induce severe autoimmunity.

PATIENTS AND METHODS

We measured by enzyme-like immunosorbent assay serum and cerebrospinal fluid (CSF) levels of IL-15, IL-12, and IL-17 in 24 patients with CIDP and 12 patients with other non-inflammatory neurological disorders and serum levels in 16 healthy subjects.

RESULTS

We found a positive association of CSF IL-12 (P = 0·012) with CIDP presence (P<0·001).

CONCLUSIONS

Our findings suggest that IL-12 may be involved as potential marker of immune activation in CIDP. The increase in its levels in CSF may be a marker of initiation of Th-1 cell-mediated immunity.

The role of cytokines in Guillain-Barré syndrome

Cytokines play an important role in the pathogenesis of autoimmune diseases including Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN). In this article, we reviewed the current knowledge of the role of cytokines such as TNF-α, IFN-γ, IL-1β, IL-6, IL-12, IL-18, IL-23, IL-17, IL-10, IL-4 and chemokines in GBS and EAN as unraveled by studies both in the clinic and the laboratory. However, these studies occasionally yield conflicting results, highlighting the complex role that cytokines play in the disease process. Efforts to modulate cytokine function in GBS and other autoimmune disease have shown efficiency indicating that cytokines are important therapeutic targets.

Intranasal immune challenge induces sex-dependent depressive-like behavior and cytokine expression in the brain

The association between activation of the immune system and mood disorders has been reported by several studies. However, the mechanisms by which the immune system affects mood are only partially understood. In the present study, we detected depressive-like behavior in a rat animal model which involves the induction of inflammation in the nasal cavities by intranasal (i.n.) instillation of bacterial lipopolysaccharides (LPS). Female rats showed depressive-like behavior as evidenced by the forced swim test after repeated i.n. administration of LPS. These responses were not paralleled by alterations in motor activity as measured by the open field test. In the same animals, corticosterone responses after the swimming sessions were the highest of all the groups evaluated. Real-time RT PCR was used to analyze the transcriptional regulation of the cytokines interleukin-1beta, tumor necrosis factor-alpha, and interleukin-6 in several brain regions. Increased tumor necrosis factor-alpha was detected in the hippocampus and brainstem of female rats challenged with i.n. LPS. These results suggest that peripheral inflammation in the upper respiratory tract is an immune challenge capable of inducing depressive-like behavior, promoting exaggerated glucocorticoid responses to stress, and increasing cytokine transcription in the brain. These results further our understanding of the role that the immune system may play in the pathophysiology of depression.

Can nasal drug delivery bypass the blood-brain barrier?: questioning the direct transport theory

The connection between the nasal cavity and the CNS by the olfactory neurones has been investigated extensively during the last decades with regard to its feasibility to serve as a direct drug transport route to the CSF and brain. This drug transport route has gained much interest as it may circumvent the blood-brain barrier (BBB), which prevents some drugs from entering the brain. Approximately 100 published papers mainly reporting animal experiments were reviewed to evaluate whether the experimental design used and the results generated provided adequate pharmacokinetic information to assess whether the investigated drug was transported directly from the olfactory area to the CNS. In the analysis the large anatomical differences between the olfactory areas of animals and humans and the experimental conditions used were evaluated. The aim of this paper was to establish the actual evidence for the feasibility of this direct transport route in humans. Twelve papers presented a sound experimental design to study direct nose to CNS transport of drugs based on the authors' criteria. Of these, only two studies in rats were able to provide results that can be seen as an indication for direct transport from the nose to the CNS. No pharmacokinetic evidence could be found to support a claim that nasal administration of drugs in humans will result in an enhanced delivery to their target sites in the brain compared with intravenous administration of the same drug under similar dosage conditions.

Role of neuronal interferon-gamma in the development of myelopathy in rats infected with human T-cell leukemia virus type 1

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of not only adult T-cell leukemia but also HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Among the rat strains infected with HTLV-1, chronic progressive myelopathy, named HAM rat disease, occurs exclusively in WKAH rats. In the present study, we found that HTLV-1 infection induces interferon (IFN)-gamma production in the spinal cords of HAM-resistant strains but not in those of WKAH rats. Neurons were the major cells that produced IFN-gamma in HTLV-1-infected, HAM-resistant strains. Administration of IFN-gamma suppressed expression of pX, the gene critically involved in the onset of HAM rat disease, in an HTLV-1-immortalized rat T-cell line, indicating that IFN-gamma protects against the development of HAM rat disease. The inability of WKAH spinal cord neurons to produce IFN-gamma after infection appeared to stem from defects in signaling through the interleukin (IL)-12 receptor. Specifically, WKAH-derived spinal cord cells were unable to up-regulate the IL-12 receptor beta2 gene in response to IL-12 stimulation. We suggest that the failure of spinal cord neurons to produce IFN-gamma through the IL-12 pathway is involved in the development of HAM rat disease.

The critical role of IL-12p40 in initiating, enhancing, and perpetuating pathogenic events in murine experimental autoimmune neuritis

Interleukin 12 (IL-12) is a proinflammatory cytokine with important immunoregulatory activities and is critical in determining the differentiation and generation of Th1 cells. For the present study, we investigated the role of endogenous IL-12 in the pathogenesis of experimental autoimmune neuritis (EAN), which is a CD4+ T-cell mediated autoimmune inflammatory disease of the peripheral nervous system. EAN is used as an animal model for Guillain-Barré syndrome of humans. Here, EAN was established in IL-12 p40 deficient mutant (IL-12-/-) C57BL/6 mice by immunization with P0 peptide 180-199, a purified component of peripheral nerve myelin, and Freund's complete adjuvant. In these IL-12-/- mice the onset of clinical disease was delayed, and the incidence and severity of EAN were significantly reduced compared to that in wild-type mice.The former group's clinical manifestations were associated with less P0-peptide 180-199 induced secretion of interferon-gamma (IFN-gamma) by splenocytes in vitro and low production of anti-P0-peptide 180-199 IgG2b antibodies in serum. Fewer IFN-gamma and TNF-alpha producing cells, but more cells secreting IL-4, were found in sciatic nerve sections from IL-12-/- mice, consistent with impaired Th1 functions and response. However, the IL-12 deficiency appeared not to affect P0 peptide 180-199-specific T-cell proliferation. These results indicate that IL-12 has a major role in the initiation, enhancement and perpetuation of pathogenic events in EAN by promoting a Th1 cell-mediated immune response and suppressing the Th2 response. This information augments consideration of IL-12 as a therapeutic target in Guillain-Barré syndrome and other T-cell-mediated autoimmune diseases.

CD4+/CD8+ macrophages infiltrating at inflammatory sites: a population of monocytes/macrophages with a cytotoxic phenotype

We found a population of nonlymphoid cells expressing both CD4 and CD8 in peripheral blood mononuclear cells (PBMCs) of human T-cell leukemia virus type-I pX transgenic rats with autoimmune diseases. These cells, which showed a monocytic phenotype, were also found in wild-type rats, and their number increased by adjuvant-assisted immunization. GM-CSF increased the number of these double-positive (DP) monocytes in PBMCs. Consistent with the idea that DP monocytes differentiate into DP macrophages at sites of inflammation, we found infiltration of DP macrophages at the site of myosin-induced myocarditis in wild-type rats; these cells exhibited a T-helper 1 (Th1)-type cytokine/chemokine profile and expressed high levels of Fas ligand, perforin, granzyme B, and NKR-P2 (rat orthologue of human NKG2D). Adoptive transfer of GFP-positive spleen cells confirmed hematogenous origin of DP macrophages. DP monocytes had a cytotoxic phenotype similar to DP macrophages, indicating that this phenotypic specialization occurred before entry into a tissue. In line with this, DP monocytes killed tumor cells in vitro. Combined evidence indicates that certain inflammatory stimuli that induce GM-CSF trigger the expansion of a population of DP monocytes with a cytotoxic phenotype and that these cells differentiate into macrophages at inflammatory sites. Interestingly, human PBMCs also contain DP monocytes.

Increased susceptibility to experimental autoimmune neuritis after upregulation of the autoreactive T cell response to peripheral myelin antigen in apolipoprotein E-deficient mice

Experimental autoimmune neuritis (EAN), an acute demyelinating inflammatory disease of the peripheral nervous system (PNS), is a good model for the human counterpart, Guillain-Barré syndrome. Apolipoprotein E (ApoE), a 34 kDa glycosylated protein with multiple biological properties, has been linked both with the innate immune response of mice and with neurological disease. The present study investigated the previously unexplored role of ApoE in autoimmune-mediated demyelination. ApoE-deficient (apoE -/-) mice exhibited a greater susceptibility to EAN induced by the PNS myelin P0 protein peptide 180-199, as compared to wild type (apoE +/+) mice. The augmented susceptibility seen in apoE -/- mice was associated with increased inflammatory cell infiltrates in the PNS during the effector phase. Although the 2 groups of mice exhibited no quantitative or proportional differences in splenic lymphocyte populations, the apoE -/- mice showed enhanced antigen-specific proliferation of T cells of spleen, which is related to modified macrophage function, upregulation of Th1 and downregulation of Th2-autoreactive responses to P0 peptide. These effects were shown as increased numbers of IFN-gamma expressing cells in the spleen and of IFN-gamma, IL-12 and TNF-alpha expressing cells in the PNS, as well as a decreased IL-10 production by splenic cells in apoE -/- mice. In addition, apoE -/- mice had enhanced antigen-specific antibody responses, which might have contributed to their aggravated EAN. These data provide strong evidence that apoE acts as an inhibitor of this inflammatory and demyelinating disease by upregulating IL-10, as well as by inhibiting Th1 responses and antigen-specific antibody formation. These data may aid the development of new and more effective therapeutic strategies for inflammatory and demyelinating diseases such as Guillain-Barré syndrome.