In vitro activation of CD8 interphotoreceptor retinoid-binding protein-specific T cells requires not only antigenic stimulation but also exogenous growth factors

Role of autoreactive Tc17 cells in the pathogenesis of experimental autoimmune encephalomyelitis

Background

The pathogenesis of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE—an animal model of MS) is primarily mediated by T cells. However, recent studies have only focused on interleukin (IL)‐17‐secreting CD4+ T‐helper cells, also known as Th17 cells. This study aimed to compare Th17 cells and IL‐17‐secreting CD8+ T‐cytotoxic cells (Tc17) in the context of MS/EAE.

Methods

Female C57BL/6 mice were immunized with myelin oligodendrocyte glycoprotein peptides 35–55 (MOG35–55), pertussis toxin, and complete Freund's adjuvant to establish the EAE animal model. T cells were isolated from the spleen (12–14 days postimmunization). CD4+ and CD8+ T cells were purified using isolation kit and then differentiated into Th17 and Tc17, respectively, using MOG35–55 and IL‐23. The secretion levels of interferon‐γ (IFN‐γ) and IL‐17 were measured via enzyme‐linked immunosorbent assay using cultured CD4+ and CD8+ T cell supernatants. The pathogenicity of Tc17 and Th17 cells was assessed through adoptive transfer (tEAE), with the clinical course assessed using an EAE score (0–5). Hematoxylin and eosin as well as Luxol fast blue staining were used to examine the spinal cord. Purified CD8+ CD3+ and CD4+ CD3+ cells differentiated into Tc17 and Th17 cells, respectively, were stimulated with MOG35–55 peptide for proliferation assays.

Results

The results showed that Tc17 cells (15,951 ± 1985 vs. 55,709 ± 4196 cpm; p < 0.050) exhibited a weaker response to highest dose (20 μg/mL) MOG35–55 than Th17 cells. However, this response was not dependent on Th17 cells. After the 48 h stimulation, at the highest dose (20 μg/mL) of MOG35–55. Tc17 cells secreted lower levels of IFN‐γ (280.00 ± 15.00 vs. 556.67 ± 15.28 pg/mL, p < 0.050) and IL‐17 (102.67 ± 5.86 pg/mL vs. 288.33 ± 12.58 pg/mL; p < 0.050) than Th17 cells. Similar patterns were observed for IFN‐γ secretion at 96 and 144 h. Furthermore, Tc17 cell‐induced tEAE mice exhibited similar EAE scores to Th17 cell‐induced tEAE mice and also showed similar inflammation and demyelination.

Conclusion

The degree of pathogenicity of Tc17 cells in EAE is lower than that of Th17 cells. Future investigation on different immune cells and EAE models is warranted to determine the mechanisms underlying MS.

Characterization of myelin oligodendrocyte glycoprotein (MOG)35-55-specific CD8+ T cells in experimental autoimmune encephalomyelitis

Background:

The pathogenesis of multiple sclerosis (MS) is mediated primarily by T cells, but most studies of MS and its animal model, experimental autoimmune encephalomyelitis (EAE), have focused on CD4⁺ T cells. The aims of the current study were to determine the pathological interrelationship between CD4 and CD8 autoreactive T cells in MS/EAE.

Methods:

Female C57BL/6 mice (n = 20) were induced by myelin oligodendrocyte glycoprotein (MOG)_35–55 peptide. At 14 days after immunization, T cells were isolated from the spleen and purified as CD4⁺ and CD8⁺ T cells by using CD4 and CD8 isolation kits, and then the purity was determined by flow cytometric analysis. These cells were stimulated by MOG_35–55 peptide and applied to proliferation assays. The interferon-gamma (IFN-γ) and interleukin (IL)-4 secretion of supernatant of cultured CD4⁺ and CD8⁺ T cells were measured by enzyme-linked immunosorbent assays (ELISA). For adoptive transfer, recipient mice were injected with MOG_35–55-specific CD8⁺ or CD4⁺ T cells. EAE clinical course was measured by EAE score at 0–5 scale and spinal cord was examined by staining with hematoxylin and eosin and Luxol fast blue staining.

Results:

CD8⁺CD3⁺ and CD4⁺CD3⁺ cells were 86% and 94% pure of total CD3⁺ cells after CD8/CD4 bead enrichment, respectively. These cells were stimulated by MOG_35–55 peptide and applied to proliferation assays. Although the CD8⁺ T cells had a generally lower response to MOG_35–55 than CD4⁺ T cells, the response of CD8⁺ T cells was not always dependent on CD4. CD8⁺ T cell secreted less IFN-γ and IL-4 compared with CD4⁺ T cells. EAE was induced in wildtype B6 naïve mice by adoptive transfer of MOG_35–55-specific T cells from B6 active-induced EAE (aEAE) mice. A similar EAE score and slight inflammation and demyelination were found in naive B6 mice after transferring of CD8⁺ T cells from immunized B6 mice compared with transfer of CD4⁺ T cells.

Conclusion:

Our data suggest that CD8⁺ autoreactive T cells in EAE have a lower encephalitogenic function but are unique and independent on pathogenic of EAE rather than their CD4⁺ counterparts.

Re-programming immunosurveillance in persistent non-infectious ocular inflammation

Ocular function depends on a high level of anatomical integrity. This is threatened by inflammation, which alters the local tissue over short and long time-scales. Uveitis due to autoimmune disease, especially when it involves the retina, leads to persistent changes in how the eye interacts with the immune system. The normal pattern of immune surveillance, which for immune privileged tissues is limited, is re-programmed. Many cell types, that are not usually present in the eye, become detectable. There are changes in the tissue homeostasis and integrity. In both human disease and mouse models, in the most extreme cases, immunopathological findings consistent with development of ectopic lymphoid-like structures and disrupted angiogenesis accompany severely impaired eye function. Understanding how the ocular environment is shaped by persistent inflammation is crucial to developing novel approaches to treatment.

Blockade of Extracellular ATP Effect by Oxidized ATP Effectively Mitigated Induced Mouse Experimental Autoimmune Uveitis (EAU)

Various pathological conditions are accompanied by ATP release from the intracellular to the extracellular compartment. Extracellular ATP (eATP) functions as a signaling molecule by activating purinergic P2 purine receptors. The key P2 receptor involved in inflammation was identified as P2X7R. Recent studies have shown that P2X7R signaling is required to trigger the Th1/Th17 immune response, and oxidized ATP (oxATP) effectively blocks P2X7R activation. In this study we investigated the effect of oxATP on mouse experimental autoimmune uveitis (EAU). Our results demonstrated that induced EAU in B6 mice was almost completely abolished by the administration of small doses of oxATP, and the Th17 response, but not the Th1 response, was significantly weakened in the treated mice. Mechanistic studies showed that the therapeutic effects involve the functional change of a number of immune cells, including dendritic cells (DCs), T cells, and regulatory T cells. OxATP not only directly inhibits the T cell response; it also suppresses T cell activation by altering the function of DCs and Foxp3⁺ T cell. Our results demonstrated that inhibition of P2X7R activation effectively exempts excessive autoimmune inflammation, which may indicate a possible therapeutic use in the treatment of autoimmune diseases.

Amelioration of experimental autoimmune uveoretinitis by aldose reductase inhibition in Lewis rats

PURPOSE

Recently, the authors showed that the inhibition of aldose reductase (AR) prevents bacterial endotoxin-induced uveitis in rats. They have now investigated the efficacy of AR inhibitors in the prevention of experimental autoimmune-induced uveitis (EAU) in rats.

METHODS

Lewis rats were immunized with bovine interphotoreceptor retinoid-binding peptide (IRBP) to develop EAU. Two or 8 days after immunization, the rats started receiving the AR inhibitor fidarestat (7 mg/kg/d; intraperitoneally). They were killed when the disease was at its peak; aqueous humor (AqH) was collected from one eye, and the other eye of each rat was used for histologic studies. The protein concentration and the levels of inflammatory markers were determined in AqH. Immunohistochemical analysis of eye sections was performed to determine the expression of inflammatory markers. The effect of AR inhibition on immune response was investigated in isolated T lymphocytes.

RESULTS

Immunization of rats by IRBP peptide resulted in a significant infiltration of leukocytes in the posterior and the anterior chambers of the eye. Further, EAU caused an increase in the concentration of proteins, inflammatory cytokines, and chemokines in AqH, and the expression of inflammatory markers such as inducible-nitric oxide synthase and cycloxygenase-2 in the rat eye ciliary bodies and retina. Treatment with fidarestat significantly prevented the EAU-induced ocular inflammatory changes. AR inhibition also prevented the proliferation of spleen-derived T cells isolated from EAU rats in response to the IRBP antigen.

CONCLUSIONS

These results suggest that AR could be a novel mediator of bovine IRBP-induced uveitis in rats.

IL-22-induced regulatory CD11b+ APCs suppress experimental autoimmune uveitis

We have previously reported that IL-17(+) interphotoreceptor retinoid-binding protein (IRBP) 161-180-specific T cells have a strong pathogenic effect in experimental autoimmune uveitis (EAU) induced in B10RIII mice; however, this pathogenic activity is not solely attributable to the major cytokine, IL-17, produced by these cells. To determine whether other cytokines produced by Th17 cells show a stronger association with their pathogenic activity, we studied the role of IL-22 in EAU. IL-22 is one of the major cytokines produced by these cells. Our results showed that administration of small doses of IL-22 to EAU-susceptible mice significantly reduced the severity of EAU. In addition, mice treated with IL-22 generated decreased numbers of IFN-γ(+) and IL-17(+) uveitogenic T cells, but increased numbers of Foxp3(+) regulatory T cells. Mechanistic studies showed that the effect of the injected IL-22 was on CD11b(+) APCs, which expressed increased levels of IL-22R during induction of disease following immunization with uveitogenic Ag. In vitro IL-22 treatment of CD11b(+) APCs collected from Ag-primed mice resulted in increased expression of programmed death ligand-1 and the production of increased amounts of IL-10 and TGF-β. Moreover, IL-22-treated CD11b(+) APCs caused IRBP161-180-specific T cells to lose their uveitogenic activity and acquire immunosuppressive activity, which suppressed the induction of EAU by additional pathogenic IRBP161-180-specific effector T cells.

Regulatory effect of gammadelta T cells on IL-17+ uveitogenic T cells

PURPOSE

To characterize the regulatory effect of gammadelta T cells in the activation of IL-17+ uveitogenic T cells.

METHODS

The authors administered the gammadelta TCR-specific antibody GL3 to B6 mice before or after antigen immunization and examined Th1- or Th17-polarized T-cell responses. The intensity of Th17 responses was also examined in responder T cells containing varying numbers of gammadelta T cells.

RESULTS

GL3 treatment resulted in varying degrees of depletion of circulating gammadelta T cells, depending on when the antibody was administered. The intensity of the alphabetaTCR+IL-17+, but not the alphabetaTCR+IFN-gamma+, IRBP-specific T-cell responses was correlated to the percentage of gammadelta T cells in the responder T cells. Kinetic studies showed that early IL-17+ T cells were primarily gammadelta T cells, with a later gradual shift to alphabeta T cells. A close association was seen between the intensity of the IL-17+ autoreactive T-cell response and the percentage of gammadelta T cells in the responder T cells. Although a modest increase in gammadelta T cells among the responder T cells promoted the expansion of IL-17+ alphabetaTCR+ T cells, a higher proportion of gammadelta T cells inhibited it.

CONCLUSIONS

gammadelta T cells are actively involved in the generation of alphabetaTCR+IL-17+ T cells. The number of gammadelta T cells and the alphabeta/gammadelta T-cell ratio in the responder T cells regulate the intensity of the Th17-type autoreactive T-cell response.

Major role of gamma delta T cells in the generation of IL-17+ uveitogenic T cells

We show that in vitro activation of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells from C57BL/6 mice immunized with an uveitogenic IRBP peptide (IRBP(1-20)) under TH17-polarizing conditions is associated with increased expansion of T cells expressing the gammadelta TCR. We also show that highly purified alphabeta or gammadelta T cells from C57BL/6 mice immunized with IRBP(1-20) produced only small amounts of IL-17 after exposure to the immunizing Ag in vitro, whereas a mixture of the same T cells produced greatly increased amounts of IL-17. IRBP-induced T cells from IRBP-immunized TCR-delta(-/-) mice on the C57BL/6 genetic background produced significantly lower amounts of IL-17 than did wild-type C57BL/6 mice and had significantly decreased experimental autoimmune uveitis-inducing ability. However, reconstitution of the TCR-delta(-/-) mice before immunization with a small number of gammadelta T cells from IRBP-immunized C57BL/6 mice restored the disease-inducing capability of their IRBP-specific T cells and greatly enhanced the generation of IL-17(+) T cells in the recipient mice. Our study suggests that gammadelta T cells are important in the generation and activation of IL-17-producing autoreactive T cells and play a major role in the pathogenesis of experimental autoimmune uveitis.

Mouse gammadelta T cells are capable of expressing MHC class II molecules, and of functioning as antigen-presenting cells

Although human and bovine gammadelta T cells were shown to express MHC class II antigen and function as APCs, attempts to determine if mouse gammabeta T cells have similar functions remained unsuccessful. We now show that gammadelta T cells derived from immunized mice also can be induced to express MHC class II and co-stimulatory molecules after activation in vitro, and are capable of antigen presentation. Using highly purified gammadelta T cells, we found that, unlike human gammadelta T cells, the expression of MHC class II molecules by mouse gammadelta T cells is limited to newly activated cells. Highest levels of MHC class II expression were seen on activated gammadelta T cells that had lost most surface-expressed gammadelta TCR while exhibiting increased levels of intracellular gammadelta TCR. In the absence of further stimulation, MHC class II expression gradually declined with the gammadelta T cells regaining their surface TCR. We also show that cytokine-activated gammadelta T cells can also express MHC class II antigen and exercise antigen-presenting activity.

Sequence 168 to 177 of interphotoreceptor retinoid-binding protein (IRBP) is an antigenic epitope for autoreactive CD8 T cells in the B10RIII mouse

We previously demonstrated that a significant proportion of interphotoreceptor retinoid-binding protein (IRBP)-specific uveitogenic T cells in the C57BL/6 mouse and Lewis rat express CD8. The aims of this study were to determine whether some of the IRBP-specific T cells in the B10RIII mouse also express CD8 and whether CD8 and CD4 IRBP-specific T cells in the B10RIII mouse recognize a different or the same antigenic epitope. Our results show that autoreactive CD8 T cells were abundant in B10RIII mice immunized with the uveitogenic peptide IRBP161-180. Using multimers of recombinant H-2D(r) molecules, we also showed that the binding of the H-2D(r) fusion protein to IRBP161-180-expanded CD8 T cells was dependent on the peptide complexed with the recombinant molecules. The use of a panel of truncated peptides showed that the truncated 10-mer peptide, IRBP168-177, retained the ability to bind to, and stimulate, IRBP161-180-specific CD8 T cells after complexing with a dimeric MHC class I (H-2D(r)) molecule. Finally, adoptive transfer of IRBP161-180-specific T cells stimulated with IRBP168-177 consistently induced mild, but significant, EAU in naïve B10RIII mice.

Characterization of IL-17+ interphotoreceptor retinoid-binding protein-specific T cells in experimental autoimmune uveitis

PURPOSE

The aims of this study were to determine whether IL-17(+) T cells were present in CD4 and CD8 interphotoreceptor retinoid-binding protein (IRBP)-specific T cells and to determine the role of antigen-specific and nonspecific IL-17(+) T cells in the pathogenesis of experimental autoimmune uveitis (EAU).

METHODS

B6 mice were immunized with uveitogenic peptide IRBP1-20. In vivo-primed T cells were separated and stimulated with the immunizing peptide. Intracellular expression of IFN-gamma and IL-17 by the T cells was assessed, and the pathogenic activity of the activated T cells was determined.

RESULTS

A subset of autoreactive IRBP-specific CD8 T cells expressed IL-17. IRBP-specific T cells preferentially expressed IL-17 when expanded by IL-23, whereas IFN-gamma-expressing cells were dominant when the T cells were cultured with IL-2. Importantly, both expanded T-cell populations were uveitogenic. In addition, IL-23 promoted the expansion of antigen-specific and non-antigen-specific IL-17(+) T cells, whereas TGF-beta and IL-6 acted only on non-antigen-specific IL-17(+) T cells. Only the antigen-specific IL-17(+) T cells were uveitogenic. The activation of autoreactive IL-17(+) T cells was markedly increased in vivo by the mycobacterial component of CFA and pertussis toxin (PTX) and in vitro by the ligation of Toll-like receptors.

CONCLUSIONS

IL-17(+) T cells can be readily detected among activated autoreactive and bystander T cells and may play a major role in the pathogenesis of EAU.

Minimally activated CD8 autoreactive T cells specific for IRBP express a high level of Foxp3 and are functionally suppressive

PURPOSE

Results in previous reports have demonstrated that immunization of the EAU-prone B6 mouse activates both CD4 and CD8 IRBP-specific T cells. The purpose of this study was to investigate structural and functional differences between CD4 and CD8 autoreactive T cells activated by the uveitogenic peptide.

METHODS

Purified CD4 and CD8 isolated from B6 mice immunized with an uveitogenic peptide, interphotoreceptor retinoid-binding protein (IRBP)1-20, were stimulated in vitro with various doses of immunizing peptide. The activated T cells were determined for cytokine production, expression of Foxp3, and suppressor activity.

RESULTS

CD4 autoreactive T cells underwent full activation when stimulated with high or medium concentrations of immunizing peptide, whereas a high dose of antigenic peptide resulted in only modest activation of CD8 autoreactive T cells. When stimulated by a low dose (<0.1 microg/mL) of antigen or by of a high dose of antigen and a small amount of TGF-beta1, the minimally activated CD8 T cells expressed a high level of Foxp3 and gained suppressor function.

CONCLUSIONS

Minimally activated CD8 autoreactive T cells can be functionally suppressive and may neutralize the tissue-damaging effect of the CD4 autoreactive T cells.

Suppression of established experimental autoimmune uveitis by anti-LFA-1alpha Ab

PURPOSE

To identify costimulatory molecules that are important in the effector phase of experimental autoimmune uveitis (EAU).

METHODS

EAU was induced in C57BL/6 (B6) mice by transfer of activated T cells specific for the interphotoreceptor-binding protein (IRBP) 1-20 peptide. The animals were then treated with and without anti-leukocyte function associated antigen (LFA)-1alpha mAb, at day 0 or 10 (disease onset) after T-cell transfer. Clinical signs of inflammation, ocular histology, and infiltrated inflammatory cells in the eye were compared. The primary and secondary proliferative responses of uveitogenic CD4 and CD8 T cells were tested after treatment with costimulatory blockers in vivo and in vitro. Moreover, the abilities of uveitogenic T cell trafficking and their interaction with retinal astrocytes were examined.

RESULTS

Anti-LFA-1alpha Abs caused significant suppression of disease when administered either at the time of effector uveitogenic T cell transfer or at disease onset. Studies of the mechanisms by which anti-LFA-1alpha Ab inhibits the effector phase of uveitis demonstrated that it blocks multiple pathogenic events of uveitis mediated by IRBP-specific uveitogenic T cells, including the activation of T cells outside and inside the eye and the trafficking of activated autoreactive T cells into the inflammatory site. In addition, Ab treatment selectively suppressed the activation and expansion of pathogenic, but not regulatory, T cells in vivo.

CONCLUSIONS

Anti-LFA-1alpha Abs are potent inhibitors of established autoimmune uveitis and that such treatment may be applicable not only for the prevention, but also the treatment, of T-cell-mediated autoimmune diseases.

The net effect of costimulatory blockers is dependent on the subset and activation status of the autoreactive T cells

In this study, we investigated whether CD4 and CD8 autoreactive T cells have different costimulatory requirements for their activation in vitro by testing the effect of a panel of Abs specific for various costimulatory molecules. Our results showed that CD8 interphotoreceptor retinoid-binding protein-specific T cells are more dependent on costimulatory molecules for activation than their CD4 counterparts. Interphotoreceptor retinoid-binding protein-specific T cells are less dependent on costimulatory molecules in the secondary response than the primary response. We also showed that blockade of costimulatory molecules can either promote or inhibit the proliferation of autoreactive T cells, depending on the degree of activation of the cells. Our results show that anti-costimulatory molecule treatment can have diverse actions on autoreactive T cell subsets, the net effect being determined by the subset of immune cells affected and the type and dose of treatment used.

The role of cytokines in the regulation of ocular autoimmune inflammation

The eye is a unique place for the development of an immune response. Beyond the usual mechanisms of immune restraint, the eye evolved with its exclusive mechanisms such as anterior chamber associated immune deviation. Therefore, immune-mediated inflammation in the eye does not develop at the same pace as in other sites of the body. Here we will address such peculiarities as they regard to ocular autoimmunity, using the experimental autoimmune uveitis as a model to understand the participation of cytokines in the process of aggression against the eye, as well as their immunoregulatory role.