Experimental immune-mediated blepharoconjunctivitis in rats induced by immunization with ragweed pollen

Conjunctival infiltrates and cytokines in an experimental immune-mediated blepharoconjunctivitis rat model

Purpose

To characterize the histopathological and immunological findings of a rat model of allergic blepharoconjunctivitis (BC) and demonstrate its potential utility for the assessment of BC therapies.

Methods

Sprague-Dawley (SD) rats were immunized with ovalbumin (OVA) and topically challenged with OVA (BC group) or PBS (control group), while a corticosteroid group was pre-treated with triamcinolone acetate 24 h before the challenge. Morphological features were evaluated and tissues were harvested for histological, flow cytometry and cytokine analysis.

Results

The BC group rats developed eyelid excoriations, redness, and conjunctival edema 24 h after the OVA challenge, while corticosteroid pre-treated and PBS-challenged rats were unaffected. The BC features were reduced despite repeated challenges for 5 days. Massive immune cell infiltration was observed in conjunctivae of BC rats, while no significant infiltration was seen in the other groups. Populations of T cells, mono-macrophages, neutrophils, and NK cells made up more than 77% of CD45⁺7AAD^- cells in the conjunctival tissues. T cell proportions were increased at 96 h compared to 24 h post-challenge, while macrophages decreased during the same time period. Eosinophils and intraepithelial neutrophils were detected in the BC rats, but not in the PBS and corticosteroid groups. BC eyes had significantly higher levels of IFN-γ and IL-2, while IL-4 and IL-6 levels were similar to controls.

Conclusion

A robust BC response was detected in this rat model which was suppressed by corticosteroid pre-treatment. Immune cell composition and cytokine profiles changed over time.

Ocular redness - II: Progress in development of therapeutics for the management of conjunctival hyperemia

Conjunctival hyperemia is one of the most common causes for visits to primary care physicians, optometrists, ophthalmologists, and emergency rooms. Despite its high incidence, the treatment options for patients with conjunctival hyperemia are restricted to over-the-counter drugs that provide symptomatic relief due to short duration of action, tachyphylaxis and rebound redness. As our understanding of the immunopathological pathways causing conjunctival hyperemia expands, newer therapeutic targets are being discovered. These insights have also contributed to the development of animal models for mimicking the pathogenic changes in microvasculature causing hyperemia. Furthermore, this progress has catalyzed the development of novel therapeutics that provide efficacious, long-term relief from conjunctival hyperemia with minimal adverse effects.

Evaluation of eosinophilic inflammation in a novel murine atopic keratoconjunctivitis model induced by crude Dermatophagoides farinae antigen

BACKGROUND

The purpose of this study is to conduct a histopathological research of the conjunctival findings and eosinophilic inflammation of novel atopic keratoconjunctivitis in a NC/Nga mouse model using crude Dermatophagoides farina.

METHODS

NC/Nga mice were sensitized by repeated topical applications of an ointment containing Dermatophagoides farinae body (Dfb). They were then divided into 4 groups depending on the following topical ophthalmic treatment: DFb group undergoing topical ophthalmic ointment containing Dfb; DFco group undergoing topical instillation of allergen extracts of Dermatophagoides farinae; Ba group undergoing topical ointment with substrate alone and NT group without after-topical ophthalmic treatment. At 24 hours after the last ophthalmic treatment, histopathological examination was performed. The density of the subepithelial infiltration of the eosinophils was determined. Serum total IgE and house-dust-mite (HDM)-specific IgE antibody concentrations were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

In the DFb group, the conjunctiva showed similar findings to those of atopic keratoconjunctivitis, i.e. intraepithelial pseudotubular formation, Torus-form infiltration due to massive lymphocytes in the palpebral conjunctiva and gelatinous hyperplasia in the limbus with subepithelial granuloma composed of lymphocytes and eosinophils. Subepithelial infiltration of eosinophil density in the DFb group [878.4 ± 399.7cells/mm2 (mean ± SD)] was significantly higher than in the other 2 groups (DFco 85.6 ± 40.1 Ba 49.2 ± 32.3) (P < 0.001). Total serum IgE concentration and HDM-specific serum IgE antibody concentration in the DFb group and the DFco group were significantly higher compared with those in the NT group.

CONCLUSIONS

Topical application of an ointment containing DFb to both the skin and eyes of NC/Nga mice can induce an atopic keratoconjunctivitis (AKC) model in these mice.

Interleukin-4–Mediated Infiltration of Eosinophils into the Conjunctiva and Its Suppression by Interferon-γ

PURPOSE

Interleukin (IL)-4 is a T helper (Th)2 cytokine that plays an important role in the development of allergic reactions. It has been suggested that IL-4 is responsible for the infiltration of eosinophils into the conjunctiva during the development of allergic conjunctivitis. However, it is still unclear whether IL-4 is able to induce this eosinophilic infiltration on its own. We investigated whether subconjunctival injection of IL-4 can induce eosinophils to infiltrate into the conjunctiva.

METHODS

Brown Norway rats were subconjunctivally injected with IL-4, eotaxin, or phosphate buffered saline (PBS), and the conjunctivas were harvested for histologic analysis (including immunohistochemistry) 6, 12, 18, and 24 hr later. The harvested conjunctivas were also subjected to reverse transcription-polymerase chain reaction (RT-PCR) analysis to examine chemokine expression. In a separate experiment, the effect of coadministering interferon-gamma (IFN-gamma) along with IL-4 was examined.

RESULTS

The subconjunctival injection of IL-4 induced eosinophil infiltration into the conjunctiva in a dose-dependent manner. IL-4 was as potent as eotaxin. The eosinophilic infiltration started 6 hr after the injection and persisted for up to 24 hr after the injection. Other infiltrating cell phenotypes were noted but were also observed in conjunctivas injected with PBS alone. RT-PCR analysis demonstrated that IL-4 injection did not upregulate chemokine RNA expression in the conjunctiva. Coinjection of IFN-gamma suppressed the infiltration of eosinophils into the conjunctiva induced by IL-4 injection.

CONCLUSIONS

The subconjunctival injection of IL-4 specifically induces eosinophils to infiltrate into the conjunctiva. In addition, IFN-gamma in the conjunctiva can counteract this effect of IL-4.

Endogenous IL-17 does not play a significant role in the development of experimental murine allergic conjunctivitis

BACKGROUND

Endogenous IL-17 is needed for the Ag sensitization that results in murine allergic asthma, a Th2-mediated disease. Here, we aimed to investigate the role IL-17 plays in the development of murine experimental allergic conjunctivitis (EC) which is also a Th2-mediated disease.

METHODS

To induce EC, wild-type (WT) and IL-17-deficient (IL-17 KO) mice on the BALB/c and C57BL/6 backgrounds were immunized with ragweed (RW) in alum and challenged with RW in eye drops. Alternatively, EC was induced by adoptively transferring RW-primed splenocytes followed by challenge with RW-containing eye drops. Twenty-four hours after the RW challenge, the conjunctivas and spleens were harvested for histological analyses and cytokine assays, respectively.

RESULTS

The WT and IL-17 KO mice on both backgrounds did not differ in terms of the severity of actively induced EC, as evaluated by the conjunctival eosinophil infiltration. They also did not differ with regard to the phenotypes of the inflammatory cells infiltrating the conjunctivas, although primed IL-17 KO splenocytes stimulated in vitro with RW extract did produce significantly higher amounts of IL-4, IL-13 and IFN-gamma than WT splenocytes. Reciprocal adoptive transfer experiments also demonstrated that the IL-17 from both the donor splenocytes and the recipient mice is not involved in the development of EC.

CONCLUSIONS

Endogenous IL-17 does not appear to play a significant role in the development of EC.

Modulation of murine experimental allergic conjunctivitis by treatment with α-galactosylceramide

When mice are treated with alpha-galactosylceramide (alpha-GalCer), NKT cells are activated and suppress the development of experimental airway inflammation. This suppressive effect is believed to be mediated by the upregulation of IFN-gamma. Here, we investigated whether alpha-GalCer treatment can also modulate the development of experimental allergic conjunctivitis (EC). EC was induced in wild-type and IFN-gamma-deficient Balb/c mice by active immunization with ragweed (RW) followed by challenge with RW in eye drops. The mice were intraperitoneally injected with alpha-GalCer or vehicle at the time of immunization or before RW challenge. Twenty-four hours after RW challenge, conjunctivas, spleens and sera were harvested for histological analysis, flow cytometric, proliferation and cytokine assays, and measurement of immunoglobulin levels, respectively. Treatment with alpha-GalCer at the time of the EC-priming immunization significantly increased Th2 responses and markedly upregulated the severity of the EC. However, treatment with alpha-GalCer just before the Ag challenge that triggers EC in primed animals significantly suppressed the disease. This was associated with an increased frequency of CD4(+)CD25(+) cells, which express Foxp3, in the spleen. alpha-GalCer treatment just prior to Ag challenge also suppressed the development of EC in IFN-gamma-deficient mice, and we found apoptosis and anergy are unlikely to play a major role in the mechanism by which pre-challenge alpha-GalCer treatment suppresses EC. These data suggest that NKT cells can play a downregulatory role in the development of EC and that alpha-GalCer may be useful for treating allergic conjunctivitis.

Genetic background determines susceptibility to experimental immune-mediated blepharoconjunctivitis: Comparison of Balb/c and C57BL/6 mice

Balb/c and C57BL/6 mice have been reported to be biased towards Th2 and Th1 immune responses, respectively. We investigated which strain is more susceptible to the development of experimental immune-mediated blepharoconjunctivitis (EC), which is predominantly mediated by Th2 immune responses. EC was induced by three different methods in Balb/c and C57BL/6 mice using ragweed (RW) as the antigen. The mice were thus either actively immunized with RW, passively immunized by transfer of RW-primed T cells, or passively immunized by transfer of RW-specific IgE, followed by RW challenge in eye drops. Twenty-four hours after the challenge, conjunctivas, sera and spleens were harvested for histological analysis, measurement of serum IgE and assessment of cellular immune responses, respectively. The responses of the Balb/c and C57BL/6 mice were compared. In addition, to assess the involvement of IFN-gamma in the development of EC in the two strains, IFN-gamma knockout (GKO) mice of the two strains were actively immunized and evaluated as above. Regardless of the method of induction, EC, as determined by the degree of eosinophil infiltration into the conjunctiva, was more severe in Balb/c mice than in C57BL/6 mice. Moreover, more IgE was produced by actively immunized Balb/c mice than C57BL/6 mice and RW-primed splenocytes from Balb/c mice produced more IL-4 but less IFN-gamma than those from C57BL/6 mice. EC could be induced in the GKO mice of both strains. However, when their EC was compared to that in WT mice, significantly less infiltration of eosinophils was noted in the Balb/c GKO mice. Taken together, Balb/c mice are more susceptible to EC than C57BL/6 mice and this higher susceptibility might be related to the Th2 immune response bias of Balb/c mice. Furthermore, the involvement of endogenous IFN-gamma in the development of EC in these two strains differs.

The control of allergic conjunctivitis by suppressor of cytokine signaling (SOCS)3 and SOCS5 in a murine model

Allergic conjunctivitis (AC) is a common allergic eye disease characterized by clinical symptoms such as itchiness, conjunctival congestion, elevated Ag-specific IgE, mast cell activation, and local eosinophil infiltration. In this study we established a murine model for Ag-induced AC to understand the pathogenesis of the disease. Cell transfer experiments indicated that AC can be divided into early and late phase responses (EPR and LPR). EPR was associated with IgE responses, leading to itchiness, whereas LPR was characterized by local eosinophil infiltration. Both EPR and LPR were significantly inhibited in STAT6-deficient mice, and adoptive transfer of Th2 cells reconstituted LPR. Furthermore, SOCS3 was highly expressed at the disease site, and T cell-specific expression of SOCS3 deteriorated clinical and pathological features of AC, indicating that Th2-mediated SOCS3 expression controls the development and persistence of AC. Reduction of the expression level in SOCS3 heterozygous mice or inhibition of function in dominant-negative SOCS3 transgenic mice clearly reduced the severity of AC. In contrast, constitutive expression of SOCS5, a specific inhibitor of IL-4 signaling, resulted in reduced eosinophil infiltration. These results suggest that negative regulation of the Th2-mediated response by dominant-negative SOCS3 and SOCS5 could be a target for therapeutic intervention in allergic disease.

Animal models of allergic and inflammatory conjunctivitis

Allergic eye diseases are complex inflammatory conditions of the conjunctiva with an increasing prevalence and incidence. The diseases are often concomitant with other allergic diseases such as allergic rhinitis, atopic dermatitis and allergic asthma. Despite the disabling and prominent symptoms of ocular allergies, they are less well studied and further insights into the molecular basics are still required. To establish new therapeutic approaches and assess immunological mechanisms, animal models of ocular allergies have been developed in the past years. The major forms of allergic ocular diseases, seasonal and perennial allergic conjunctivitis, vernal and atopic keratoconjunctivitis and giant papillary conjunctivitis, each have different pathophysiological and immunological components. In contrast to these distinct entities, the current animal models are based on the sensitization against a small number of allergens such as ovalbumin, ragweed pollen or major cat allergens and consecutive challenge. Different animal species have been used so far. Starting with guinea-pig models of allergic conjunctivitis to assess pharmacological aspects, new models including rats and mice have been developed which mimic major features of ocular allergy. The presently preferred species for the investigation of the immunological basis of the disease is represented by murine models of allergic conjunctivitis. In the future, combined ocular, nasal and aerosolic challenges with allergens may provide a model of allergy that encompasses simultaneously the target organs eye, nose and airways with conjunctivitis, rhinitis and asthma.

Mast-cell activation augments the late phase reaction in experimental immune-mediated blepharoconjunctivitis

BACKGROUND

How the early phase allergic reaction affects the late phase reaction remains unclear. We examined this issue with an experimental model of allergic conjunctivitis that permits the two reactions to be disconnected from each other.

METHODS

Experimental immune-mediated blepharoconjunctivitis (EC) was initiated in Brown Norway rats by transferring ovalbumin (OVA)-specific T cells and then challenging with OVA-containing eye drops. To induce early phase reaction, a mast-cell activator, C48/80, was challenged together with or without OVA. Rats were evaluated clinically and eyes were harvested for histologic examination and for evaluation of chemokine expression by reverse-transcriptase PCR.

RESULTS

The rats challenged with OVA alone developed the T-cell-mediated late phase reaction histologically, but not clinically, in the absence of early phase reaction. While rats challenged with C48/80 with or without OVA exhibited clinical signs of the early phase reaction, the clinical late phase reaction was observed only in the OVA+C48/80 group. Eosinophilic infiltration into the conjunctiva during the late phase reaction of the OVA+C48/80 group markedly exceeded that of rats challenged with either OVA or C48/80 alone. RANTES (regulated on activation, normal T-cell expressed and secreted), an eosinophil attractant, was expressed both in the OVA+C48/80 and OVA groups, while eotaxin was expressed at equivalent levels in all three groups.

CONCLUSION

The mast-cell-mediated early phase reaction potentiates the T-cell-mediated late phase reaction, and RANTES is involved in eosinophilic infiltration induced by antigen-specific T cells. Other molecules induced by allergen-specific T cells activated in an as yet unknown manner by the mast cells may be responsible for the infiltration of eosinophils.

Differential expression and signaling of IFN-gamma in the conjunctiva between Lewis and Brown Norway rats

Genetic background determines the histological features of experimental immune-mediated blepharoconjunctivitis (EC) in rats, which is a model for human allergic conjunctivitis (AC). A great number of lymphocytes predominate in EC of Lewis rats, while less lymphocytes and more eosinophils are present in that of Brown Norway (BN) rats. Although this difference could be attributed to their systemic Th1/Th2 dominancy, it remains unclear whether some regulatory mechanisms may exist in the inflammatory site in the conjunctiva. Here, we aim to investigate this hypothesis by comparing the expression levels of inflammatory mediators in the conjunctiva between the two strains. EC was induced in Lewis and BN rats by transfer of ovalbumin (OVA)-specific CD4(+) T-cell lines followed by eye drops of OVA as antigen challenge, and then was clinically and histologically evaluated. Reverse-transcription (RT)-PCR was performed to compare the expressions of cytokines and cytokine receptors (Rs) in conjunctivas of both strains of rats either with or without EC. To confirm the biological significance of interferon (IFN)-gamma R expression, phosphorylation of signal transducers and activators of transcription (STAT)-1 was examined in the conjunctivas, followed by subconjunctival injection of IFN-gamma. BN T cells contained interleukin (IL)-4 and IFN-gamma, while Lewis T cells expressed no IL-4. Transfer of those cells induced more severe EC in Lewis rats. RTPCR using naive conjunctivas detected more IL-4, IFN-gamma, and IFN-gamma R beta-chain RNA expression in BN rats. After the EC induction, BN rats expressed significantly higher amounts of IFN-gamma R beta-chain, and upregulation of interferon regulatory factor (IRF)-1 was observed. Phosphorylation of STAT-1 was more remarkable in BN rats. The findings demonstrate differential expression of IFN-gamma R and signaling through IFN-gamma in the conjunctiva between the two strains. This may be due to differences in histopathological character between the two strains.

Exertion of the suppressive effects of IFN-gamma on experimental immune mediated blepharoconjunctivitis in Brown Norway rats during the induction phase but not the effector phase

BACKGROUND/AIMS

Interferon gamma (IFN-gamma) knockout mice exhibit severe allergic conjunctivitis (AC), indicating that IFN-gamma regulates the development of AC. The authors examined whether this inhibitory effect of IFN-gamma is exerted during the induction or effector phase of experimental AC.

METHODS

Experimental immune mediated blepharoconjunctivitis (EC) was induced in Brown Norway (BN) rats, using ovalbumin (OVA) as the antigen. To investigate the role of IFN-gamma in the induction phase, EC was induced by active immunisation and IFN-gamma (10 micro g/time, total 70 micro g), or phosphate buffered saline (PBS) as a control, was injected intraperitoneally every other day from the day of immunisation. The rats were challenged with OVA eye drops 13 days after immunisation, and 24 hours later, the eyes were harvested for histology. To examine the effects of IFN-gamma in the effector phase, OVA specific T cells were transferred into syngeneic rats and IFN-gamma (10 micro g/time, total 50 micro g) or PBS was injected each day after the transfer until induction of EC 4 days later with an OVA challenge. To investigate the role of endogenous IFN-gamma during the effector phase, an anti-IFN-gamma monoclonal antibody (3 mg/time) was injected on days 3 and 4.

RESULTS

Injection of IFN-gamma into actively immunised rats suppressed eosinophilic infiltration but not infiltration of mononuclear cells. In contrast, neither IFN-gamma nor anti-IFN-gamma affected EC in passively immunised rats.

CONCLUSION

IFN-gamma is a suppressive cytokine for the development of EC and exerts this suppressive effect during the induction phase.

Mechanism for maintenance of dominant T helper 1 immune responses in Lewis rats

Lewis rats are prone to T helper (Th) 1 immune responses, whereas Brown Norway (BN) rats are susceptible to Th2 immune responses. Yet, the precise mechanism of induction of the different outcome between these two strains remained elusive. We investigated the expression levels of some cytokines, their receptors and accessory molecules responsible for the polarization of antigen-specific immune response into a predominant Th1 or Th2 profile in Lewis and BN rats. Lymph node (LN) cells collected from rats immunized with short ragweed (RW) were used directly or after stimulation in vitro with RW for 3 days. Expression of cytokines, their receptors and accessory molecules in these LN cells were tested by reverse transcriptase-PCR. Culture supernatant was used for ELISA to detect IL-12 protein. We observed clear differences between these strains in the expression of IL-12p40, which was high in LN cells of Lewis rats even before stimulation in vitro. In addition, a higher amount of IL-12 was present in the culture supernatant in Lewis rats. Upregulation of the expression of IL-12 receptor beta1, beta2, IFN-gamma receptor alpha and beta genes were more prominent in Lewis rats rather than BN rats. Furthermore, attenuated expression of CD40 and CD40 ligand by stimulation in vitro was noted only in BN rats. Changes in expression of these molecules by stimulation as well as higher basal level of IL-12p40 might have led to the activation of Th1 cells in Lewis rats.

Effects of IL-4 and IL-12 on experimental immune-mediated blepharoconjunctivitis in Brown Norway rats

IL-12 and IL-4 are critical cytokines for Th1 and Th2 differentiation, respectively. To assess the roles of these cytokines in the development of experimental immune-mediated blepharoconjunctivitis (EC) in Brown Norway (BN) rats, their effects were tested either in vitro or in vivo. Draining lymph node cells from rats immunized with ragweed pollen (RW) in Al(OH)3 were collected and cultured for 3 days with RW in the presence of IL-4, IL-12, or PBS as a control. After harvesting the culture supernatants for cytokine ELISA and the cells for cytokine reverse transcriptase-polymerase chain reaction, 10 million cells were injected intravenously into syngeneic recipient rats (n = 12 per group). The rats were challenged with RW by eye drops 4 days after transfer. Eyes were harvested for histology 24 h later. Furthermore, IL-12 (500 ng per injection) or PBS was injected intraperitoneally every other day seven times from the day of active immunization (n = 6 per group). One day after the last injection, rats were challenged and EC was evaluated as above. Transfer of cells with IL-4 in vitro augmented eosinophilic infiltration in the conjunctiva compared with the other two groups, whereas IL-12 in vitro suppressed eosinophilic infiltration and increased lymphocytic infiltration. Interferon-gamma production was augmented by IL-12. IL-4 RNA expression was augmented by IL-4. IL-12 administration in vivo augmented lymphocytic infiltration in the conjunctiva without affecting infiltration of eosinophils. In conclusion, IL-4 and IL-12 either in vitro or in vivo augmented Th2 and Th1 immunity, respectively, thus leading to distinct histological features of EC.