Role of swarming migration in the pathogenesis of bacillus endophthalmitis

PURPOSE

Bacillus cereus causes one of the most rapidly blinding forms of bacterial endophthalmitis. Migration of B. cereus throughout the eye during endophthalmitis is a unique aspect of this disease that may contribute to intraocular virulence. This study was conducted to analyze the contribution of swarming and intraocular migration to the pathogenesis of experimental endophthalmitis.

METHODS

Eyes were injected intravitreally with 100 colony-forming units (CFU) of either wild-type, nonswarming, or swarming-complemented strains of B. cereus. Pathogenicity was compared throughout the course of infection by biomicroscopy, histology, electroretinography, and bacterial and inflammatory cell quantitation.

RESULTS

Wild-type, nonswarming, and swarming-complemented B. cereus strains grew to a similar number in the vitreous throughout the course of infection. Unlike the wild-type and swarming-complemented strains, the nonswarming mutant did not migrate to the anterior segment during infection. The rate of decrease in retinal responses of eyes infected with the all strains was similar, resulting in near complete elimination of retinal function by 12 hours. All Bacillus strains caused similar degrees of posterior segment inflammation and retinal destruction. However, the accumulation of inflammatory cells in the anterior chamber, hyphemae, and corneal ring abscesses did not occur in eyes infected with the nonswarming mutant.

CONCLUSIONS

The deficiency in swarming had little effect on retinal function loss or the overall course or severity of experimental B. cereus endophthalmitis. However, a deficiency in swarming prevented Bacillus from migrating to the anterior segment, leading to less severe anterior segment disease.

Ocular immune privilege and CTL tolerance

The introduction of antigens into the anterior chamber (AC) of the eye, an immune-privileged site, induces immune responses that effectively eliminate ocular pathogens while minimizing tissue damage that can cause blindness. This specialized immune response, termed AC associated immune deviation (ACAID) is thought to be an evolutionary compromise to preserve the delicate microanatomy of the eye while maintaining ocular immune responses. The injection of soluble antigen in the AC of mice results in systemic tolerance characterized by reduced priming for antigen-specific delayed-type hypersensitivity (DTH) and cytotoxic T lymphocyte (CTL) responses. Similarly, the injection of histo incompatible tumors into the AC of mice reduces priming for DTH responses specific to minor antigens. However, robust tumor-specific CTL responses are induced systemically following this treatment that are capable of eliminating a subsequent injection of the same tumors in the skin or the opposite eye. Interestingly, CTL responses induced by administration of tumors in the AC fail to eliminate the primary ocular tumor. In this review, we compare and contrast CTL responses generated by the injection of soluble or tumor-associated antigens in the AC and discuss mechanisms employed to induce ocular CTL tolerance.

An intravital and confocal microscopic study of the distribution of intracameral antigen in the aqueous outflow pathways and limbus of the rat eye

In a previous investigation into the fate of fluorescently labelled antigen (Ag) injected into the anterior chamber (AC) of the rat eye, a large number of Ag+ cells were noted in the conventional and non-conventional aqueous humour outflow pathways together with the external limbus. The aim of this study was to investigate the precise distribution and phenotype of these cells and compare their ability to capture fluorescent-labelled protein (bovine serum albumin, BSA, and ovalbumin, OVA) and polysaccharides (dextran, Dx) injected into the AC. The density of Ag+ cells in the iris and limbus was investigated using in vivo video fluorescence microscopy 24 hr post-injection. The distribution and phenotype of Ag+ cells in ocular tissues was analysed by confocal microscopy of frozen sections and in iris and corneoscleral/limbal wholemounts from animals sacrificed 24 hr post injection. The general distribution of labelled Ag was equivalent in OVA, BSA and Dx injected animals. Antigen-bearing cells were observed within the iris, iridocorneal angle, pre-equatorial choroid and around limbal/episcleral vessels. Localization of Ag+ cells and free Ag in the anterior segment suggests that substances of these molecular weights (40-70 kDa) leave the eye through the conventional and non-conventional aqueous outflow pathways. The cells that internalized BSA, OVA or Dx in ocular tissues were of a similar phenotype, namely, ED1+, ED2+, occasionally ED3+ and predominantly MHC class II-, thus suggesting that they are of the macrophage phenotype. However, a few Ag+ MHC class II+ dendriform cells (putative DC) were also observed in the iris, trabecular meshwork, choroid and episclera. In conclusion our data reveal that the majority of intracamerally injected soluble Ag retained in the eye is taken up by resident macrophages not only in the iris but in all tissues lining the AC of the eye.

[A study of total IgE in inflammatory pathologies of the eye anterior segment]

The paper contains data on comparative research of the IgE content in blood serum and lachrymal fluid in patients with ophthalmoherpes and with other inflammatory diseases of the eye. A higher IgE level was found in blood serum and lachrymal fluid in cases of ophthalmoherpes as well as in lachrymal fluid in cases of allergic, Chlamydia and fungus diseases of the eye. The data obtained can be used in the diagnostics of allergic eye diseases as well as in elaborating complex treatment methods for herpetic, Chlamydia and fungus lesions of the anterior eye segment. A detection of the local allergenic effect of acaricide drugs exerted on the conjunctiva and eyelids makes it obligatory to consider the above fact while treating patients with demodectic blepharoconjunctivitis.

Blood mononuclear cells induce regulatory NK T thymocytes in anterior chamber-associated immune deviation

Injection of antigen into the anterior chamber (AC) of the eye, an immunologically privileged site, is associated with the induction of immune deviation, as evidenced by T helper cell (Th) 1 to Th2 cell polarization. We recently demonstrated that AC-associated immune deviation (ACAID) is a thymus-dependent phenomenon initiated by the formation of regulatory alpha,beta T-cell receptor-positive CD4(-) CD8(-) thymocytes (THYregs). In this study, the afferent and efferent limbs of this immunoregulatory loop were traced from peripheral blood to the thymus and then to the spleen by adoptive-transfer assays. The results demonstrate that (1) F4/80(+) CD1(+) peripheral blood mononuclear cells from mice whose ACs were injected with trinitrophenol-bovine serum albumin induce the appearance of natural killer (NK) 1.1(+) THYreg in naïve recipients within 24 h of intravenous infusion; (2) these NK THYregs induce (or generate) suppressor-effector T cells in the spleens of adoptive recipients; (3) these suppressor-effector spleen cells, but not the NK THYregs themselves, directly inhibit the expression of delayed-type hypersensitivity in sensitized recipients; and (4) peripheral blood mononuclear cells from AC-injected mice do not induce ACAID in thymectomized recipients. These results confirm our hypothesis that ACAID is a model of centrally induced dominant tolerance mediated by CD-1-dependent NK T cells of recent thymic origin. The results also provide evidence of a novel tolerance induction pathway by which blood-borne antigen-presenting cells generated by antigen injection into an immunologically privileged site transport antigen to the thymus and induce the formation and export of THYreg.

Recurrent intraocular inflammation in endotoxin-induced uveitis

PURPOSE

Endotoxin-induced uveitis (EIU) in rats and mice peaks 24 hours after endotoxin injection and is commonly assumed to be a monophasic disease. This study examined intraocular inflammation at later time points to determine whether endotoxin injection can induce recurrent intraocular inflammation in strains of mice with high or moderate levels of susceptibility to EIU.

METHODS

EIU was elicited in two mouse strains with high (C3H/HeN) and moderate (FVB/N) susceptibility, by means of intraperitoneal injections of Salmonella typhimurium endotoxin. Inflammatory cells in the anterior and posterior segments of the eye were counted by a masked observer on histologic sections of eyes from 1 to 17 days after endotoxin injection.

RESULTS

A bimodal distribution of inflammatory cell infiltration was noted in eyes from C3H/HeN mice. As previously reported, inflammation peaked at 24 hours after endotoxin injection. However, a second, more pronounced peak of intraocular inflammation occurred approximately 5 days after endotoxin injection. FVB/N mice had a single peak of intraocular inflammation 4 days after injection.

CONCLUSIONS

Endotoxin injection in C3H/HeN elicits recurrent intraocular inflammation. The previously unrecognized second peak of inflammation is more severe than the initial inflammatory disease. Studies on this second inflammatory peak may be useful in determining the pathogenesis of recurrent uveitis in humans.

[Immunological status and its changes in children during surgery on anterior eye segment]

Nonspecific and specific immunity values were studied in 70 children before and in various periods after 74 operations on the anterior segment of the eyeball. In children with persistent autosensitization to ocular tissue autoantigens (alpha-crystalline and S-antigen) postoperative uveitis presented as an immunocomplex disease with signs of exhaustion of the functional potential of the phagocytosis and complement systems. In children without autosensitization uveitis was associated with immunity activation. Phagocytosis system and cooperation of lymphocyte subpopulations, including normal killers (CD16+), play an important role in prevention of sensitization to ocular tissue autoantigens. Therefore, complex immunological examinations of children before surgery and regular check-ups after it will help differentiate immunodeficiency from compensatory immunosuppression preventing autoimmune disease, which is important in prescription of immunostimulating therapy.

Endotoxin-induced uveitis is partially inhibited by anti-IL-8 antibody treatment

PURPOSE

To examine the potential therapeutic effect of a neutralizing anti-IL-8 monoclonal antibody in endotoxin-induced uveitis (EIU) in the rabbit.

METHODS

An anti-IL-8 antibody (WS-4) was injected intravitreal 2 hours before, simultaneously with, or 6 hours after endotoxin challenge in rabbits. Eyes were examined for clinical signs of inflammation, and aqueous humor (AH) was sampled to study cellular infiltration and protein content. Leukocyte subset analysis was performed on Giemsa-stained AH cytospins. Histologic grading of inflammation was performed on hematoxylin-eosin-stained sagittal sections of enucleated eyes. In separate experiments, animals received the anti-IL-8 antibody simultaneously with the endotoxin challenge, before repeated anterior chamber paracentesis was performed (at 6, 12, 24, 48, and 72 hours after injection) to estimate the kinetics and durability of changes in total cell count and protein concentration in AH.

RESULTS

Anti-IL-8 therapy caused a decrease in the clinical and histologic grade of inflammation in EIU. The mean cell count in the AH at the peak of inflammation (24 hours) in eyes receiving endotoxin only was 6419+/-1165/microl (mean +/- SE) compared to 2546+/-573/microl in rabbits treated simultaneously with 250 microg of anti-IL-8 antibody (P < 0.05). The protein concentration in the AH was not significantly altered by anti-IL-8 treatment. Kinetic analysis of the leukocyte count in the AH demonstrated persistent inhibition of leukocyte accumulation (range, 60%-91% compared to control eyes) by the anti-IL-8 antibody administered simultaneously with endotoxin. This inhibition was sustained for up to 72 hours after injection.

CONCLUSIONS

Anti-IL-8 antibody treatment partially blocks EIU in rabbits. A consistent decrease in the recruitment of polymorphonuclear leukocytes into the anterior chamber was obtained when neutralizing antibody was injected simultaneously with endotoxin. These findings suggest that IL-8 contributes to the chemotactic signal for the recruitment of leukocytes in EIU.

Effects of experimental ocular inflammation on ocular immune privilege

PURPOSE

To determine whether the inflammation of endotoxin-induced uveitis (EIU) and experimental autoimmune uveoretinitis (EAU) alters key in vivo and in vitro parameters of ocular immune privilege.

METHODS

For EIU induction, C3H/HeN mice received 200 microg lipopolysaccharide (LPS). For EAU induction, B10.A mice were immunized with 50 microg interphotoreceptor retinoid-binding protein (IRBP) mixed with complete Freund's adjuvant. Aqueous humor (AqH) was collected at periodic intervals and assayed for leukocyte content and the ability to suppress or enhance T-cell proliferation. Eyes with EAU were assessed for the capacity to support anterior chamber (AC)-associated immune deviation (ACAID) induction after injection of ovalbumin (OVA).

RESULTS

Inflammation within the anterior segment in EIU peaked at 12 to 24 hours and was detected from 10 days onward in EAU. In AqH of EIU, protein content rose within 4 hours, followed by infiltrating leukocytes. EIU AqH promptly lost its capacity to suppress T-cell proliferation and became mitogenic for T cells. In AqH of EAU, protein and leukocyte content rose at 11 days and continued to remain elevated thereafter. Whereas 11-day EAU AqH failed to suppress T-cell proliferation, AqH at later time points reacquired immunosuppressive properties. Injection of OVA into the AC of eyes of mice with EAU failed to induce ACAID.

CONCLUSIONS

The intraocular inflammation of EIU and EAU disrupted important parameters of immune privilege, ranging from breakdown of the blood- ocular barrier, to loss of an immunosuppressive microenvironment, to abrogation of ACAID. Because AqH from inflamed EAU reacquired the ability to suppress T-cell proliferation, the authors conclude that the capacity to regulate immune expression and inflammation can be a property even of inflamed eyes.

Cellular localisation and dynamics of nitric oxide synthase expression in the rat anterior segment during endotoxin-induced uveitis

The present study examined the temporal pattern and cellular localisation of nitric oxide synthase in Endotoxin-Induced Uveitis (EIU). Lewis rats (n=40) received a single footpad injection of 200 microg of bacterial lipopolysaccharide. Animals were killed at 0, 2, 4, 6, 12, 24, 48 and 72 hr after injection and ocular tissues prepared as iris-ciliary body wholemounts or frozen sections of the anterior segment. The expression of constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) was investigated at all time points by immunohistochemistry. A further group of animals (n=6) were killed at the peak of the disease (12 hr) and the cellular co-localisation of iNOS on resident and infiltrating immune cells was investigated by double immunohistochemistry utilising the biotinylated monoclonal antibodies ED1, ED2 and Ox6. Expression of cNOS on iris vessels did not alter during the course of EIU. Quantitative analysis of iris-ciliary body wholemounts revealed the first evidence of iNOS+ at 2 hr which increased dramatically at 4 and 6 hr with a peak at 12 hr. The expression of iNOS in the early phase of the disease (2-6 hr) was associated with small round marginating and newly extravasated cells that on morphological criteria were most likely neutrophils and monocytes. At 12 hr, cells of more mixed morphologies began to express iNOS and double labelling revealed 70% of these cells were also ED1(+) (a lysosomal antigen present in monocytes/macrophages and dendritic cells), 52% were Ox6(+) (MHC class II) (dendritic cells, activated macrophages and some T-cells) and 19% were ED2(+) (pan-specific resident tissue macrophages). Expressed in an alternative manner, 10% of the total ED1(+) cell population, 11% of the ED2(+) cells and 44% of Ox6(+) cells co-expressed iNOS. Expression of iNOS decreased significantly by 24 hr to near baseline levels and was absent by 48 and 72 hr. Within the ciliary processes iNOS+ dendriform cells were noted at 6 hr and accumulations of many small round iNOS+ cells were present at 12 hr. The ciliary epithelium did not at any time express iNOS at the protein level detectable by immunohistochemistry. The results of this study suggest that iNOS expression early in EIU is associated with infiltrating or newly recruited neutrophils and monocytes/macrophages in the iris whereas later in the disease resident tissue macrophages and MHC class II+ cells (activated macrophages and putative dendritic cells) in the iris and ciliary body may synthesise nitric oxide. The role of this late phase of nitric oxide synthesis may include lymphocytostasis and immunosuppression as proposed in other tissue sites. The outcome of the present study may help in planning therapeutic strategies using NOS inhibitors.

Immunoreactivity of exfoliation material for the cell adhesion-related HNK-1 carbohydrate epitope

OBJECTIVE

To study the presence of the HNK-1 epitope in exfoliation material.

METHODS

Twenty-six formalin-fixed, paraffin-embedded human eyes with exfoliation syndrome and 30 control eyes were studied immunohistochemically with monoclonal antibodies HNK-1 and VC1.1 to the HNK-1 epitope.

RESULTS

Exfoliation material reacted consistently with antibodies to the HNK-1 epitope. The zonular lamella of the lens, inner surface of the nonpigmented ciliary epithelium, and inner connective tissue layer of the ciliary body were also labeled, but the lens capsule, epithelium, and zonules were not immunoreactive. Several blood vessels of the iris showed granular immunoreaction beneath the endothelium in all exfoliation eyes and in 11 (37%) of 30 control eyes, representing older age groups.

CONCLUSIONS

The zonular lamella, nonpigmented ciliary epithelium, or the inner connective tissue layer may be responsible for the HNK-1 epitope in exfoliation material. Since this epitope is shared by many cell-adhesion molecules, its presence in exfoliation material might be of pathogenetic significance to the formation of the deposits.

Serum antiocular antibodies in patients with juvenile rheumatoid arthritis

Although the uveitis associated with juvenile rheumatoid arthritis (JRA) is presumed to have an autoimmune etiology, its pathogenesis is unknown. We utilized immunohistochemical techniques to detect the presence of serum antibodies directed against ocular tissues in these patients. The staining patterns of serum from patients with JRA, with and without uveitis, were compared with normal controls. Antibodies directed against epitopes in iris and ciliary body basement membranes, lens epithelium and fibers, Bruch's membrane, and iris and retinal blood vessels were observed in the sera of several individuals. These staining patterns were statistically more frequent among the pauciarticular and polyarticular JRA patients, with and without uveitis, than either the systemic JRA or normal populations. These results demonstrate the presence of antiocular antibodies in the sera of JRA patients, with and without uveitis. Whether those nonuveitic JRA patients with antiocular antibodies will develop uveitis is unknown at this time.

Distinctive distribution of HLA class II presenting and bone marrow derived cells in the anterior segment of human eyes

Cells of bone marrow origin that normally occupy the stroma of the murine iris and ciliary body have been implicated in the immune phenomenon, anterior chamber associated immune deviation (ACAID). Following injection of antigen into the anterior chamber, cells of this type deliver an ACAID inducing signal into the systemic circulation, presumably through the outflow tract. In an effort to identify such cells in man, anterior chambers of 34 human donor eyes of different age groups were stained immunocytochemically with monoclonal antibodies directed at HLA class II molecules, CD 45 (a molecular marker of bone marrow-derived cells) and macrophage-associated membrane molecules (CD 68, CD 14). Within the outflow tissue, the cells of the filtering trabecular meshwork stained with none of those reagents. However, infrequent single, dispersed, dendritic cells were positively stained in the intertrabecular spaces. More numerous labelled cells were found in the anterior- and posterior-most portions of the non-filtering part of the trabecular meshwork. These cells were continuous with stained cells adjacent to the outer wall of Schlemm's canal and to the collector channels. Numerous labelled cells were seen in the vicinity of the intra- and episcleral vessels, the ciliary meshwork, the stroma of the ciliary muscle and epithelial processes, and the iris stroma. With advancing age, increasing numbers of CD 45+, HLA class II expressing cells appeared to accumulate in the so-called uveoscleral pathway. These results indicate that bone marrow-derived cells with the potential to function of ACAID induction reside within human eyes, and that cells of this type are located not only in the stroma of iris and ciliary body, but within the non-filtering portions of the trabecular meshwork and the uveoscleral pathway. The appearance of rare CD 45+ cells "in transit" in the filtering trabecular meshwork is compatible with the view that cells carrying ACAID-inducing signals to the systemic immune apparatus escape from the eye by this route.

Immune response to Staphylococcus epidermidis-induced endophthalmitis in a rabbit model

Although Staphylococcus epidermidis is the most common cause of postoperative pseudophakic endophthalmitis, little is known about the immune response to S. epidermidis-induced endophthalmitis. Using a rabbit model, the immune response to an intravitreal injection of 7000 S. epidermidis (group 1) or 30,000 S. epidermidis (group 2) organisms was investigated. Clinical evaluations showed that rabbits in group 2 had a more severe inflammatory reaction in the conjunctiva, cornea, iris, and vitreous than those in group 1. The inflammatory reaction in group 1 largely resolved by day 30; group 2 continued to show a severe inflammatory response. Histopathologic findings correlated with clinical findings, with rabbits in group 2 showing a more severe inflammatory reaction in both the anterior and posterior segments of the globe. Positive vitreous cultures for S. epidermidis were present in rabbits in group 1 on days 3, 7, 10, 14, and 21 but not thereafter. However, group 2 had higher vitreous colony counts at days 3, 7, and 14 and negative vitreous cultures thereafter. Neither group showed delayed hypersensitivity to S. epidermidis antigens (evaluated by skin tests). Serum immunoglobulin (Ig) G antibody levels to phenol-inactivated S. epidermidis and glycerol teichoic acid (GTA) increased progressively, reached a peak at days 10-14, and then declined in both groups. Serum IgA antibody levels to these antigens were not detected. Group 2 had a more prolonged IgG antibody response in vitreous and aqueous than group 1. Tear fluid showed the weakest IgG and IgA antibody response to S. epidermidis and GTA. S. epidermidis-induced endophthalmitis was associated with a humoral but not a delayed hypersensitivity response to this organism.

Immunologically induced purulent anterior segment inflammation of the guinea pig eye

A single conjunctival application of ovalbumin to inbred guinea pigs (IMM/S 209) immunized with the same antigen in Freund's complete adjuvant provoked an acute purulent inflammation of the anterior segment of the eyes with a duration of up to 1 week. Intense conjunctival injection and chemosis were followed by a purulent discharge. A corneal haze was observed regularly, and a considerable proportion of the animals developed a pronounced pannus and corneal ulcers. Tear fluid cytology revealed a rapid increase in cell concentration, from the normal level (less than 10(8)/l) to greater than 10(11)/l. Seventy to 95% of the cells were polymorphonuclear leukocytes. Histological examination revealed an acute inflammatory reaction which radiated from the conjunctival fornices to the entire anterior segments of the eyes. The process was characterized by an intense oedema, vasodilation and perivascular aggregations of polymorphonuclear leukocytes, and to a lesser extent eosinophilic granulocytes which characteristically infiltrated and penetrated the epithelial layers. Neovascularization could be observed early after challenge in the stroma of all parts of the outer eye. Ulcerations of the conjunctival and corneal epithelia were observed frequently. After a number of reiterations of the antigenic challenge, a marked infiltration with lymphocytes and basophils/mast cells was observed, and significant scarring of the conjunctival mucosa developed. In several animals, a slight, but significant co-reaction of the contra-lateral, non-challenged eye was observed.

A new method for induction of experimental autoimmune uveoretinitis (EAU) in mice

Experimental autoimmune uveoretinitis (EAU) was induced in two strains of mice by repeated-immunization protocol. SMA mice (H-2 nondefined) and C57BL/6 mice (H-2b) were immunized with S-antigen mixed with Klebsiella 03 lipopolysaccharide (K03 LPS) repeatedly at intervals of 1 to 4 weeks. Following the tertiary immunization, the mice exhibited histopathological changes of EAU as well as significant immune responses to the antigen. The antigen doses required for successful EAU induction were 4 micrograms or more at each immunization time. The histopathology of EAU was characterized by mild infiltration of mononuclear cells in the retina and the choroid, particularly, at the retinal blood vessels and the photoreceptor cell layer. The anterior segment of the eye was not affected by inflammation, and therefore clinical signs of EAU were not detected even under an operating microscope. Since the mouse is a genetically and immunologically well-defined species, this model is useful for study of immunopathogenic mechanisms of EAU.

Evaluation of Ia expression in rat ocular tissues following inoculation with interferon-gamma

It is becoming increasingly clear that IFN-gamma is a potent immunoregulatory protein which influences MHC class II (Ia) antigen expression and cellular functions of B cells, T cells, NK cells and macrophages. During the past 5 yr our laboratory has provided evidence that IFN-gamma modulates class II antigens on retinal cells (retinal pigment epithelial cells, endothelial cells) and is localized within the eye during human inflammatory conditions. In this study we evaluate the direct effect of IFN-gamma on ocular tissue. Lewis rats were inoculated intravitreally or under the retina with either recombinant IFN-gamma (20,000 U) or saline. At 2 hr, 1, 2 and 6 days postinoculation, the eyes were removed and frozen sections were evaluated by immunocytochemical staining with monoclonal anti-Ia antibodies and an irrelevant monoclonal anti-T cell antibody. Saline treated tissue and tissue removed 2 hr after IFN-gamma inoculation showed no significant staining for Ia antigens. However, eyes evaluated 24 hr after IFN-gamma inoculation revealed Ia expression on a variety of ocular cells localized in the conjunctiva and anterior segment, such as conjunctival epithelium, keratocytes, iris epithelium, ciliary epithelium and choroidal cells. In the retina, retinal pigment epithelial (RPE) cells were Ia positive only when IFN-gamma was injected directly under the retina. In conjunction with Ia expression, two striking changes were noted. An iritis was seen and infiltrating cells were detected in the inner retinal layers. Both of these phenomena have been observed in certain inflammatory eye diseases. These studies clearly substantiate the concept that IFN-gamma can regulate class II antigens in the eye and thus may perpetuate immune reactivity in this site.

Immunologic evaluation of spontaneous regression of an intraocular murine melanoma

The experiments reported here describe the derivation of an immunogenic melanoma cell line from B16 melanoma by sequential in vitro mutagenization with two chemical mutagens: n-methyl n-nitro n-nitrosoguanine (MNNG) and ethane methyl sulfonate (EMS). Following in vivo screening of over 100 mutant melanoma clones, a single clone was selected for further study. When transplanted to the anterior segment of the mouse eye, the mutant melanoma (D5.1G4) underwent spontaneous resolution in 20% of the immunologically intact hosts. Tumor rejection involved extensive necrosis and culminated in phthisis of the tumor-containing eye. Histologic analysis revealed a prominent mononuclear cellular infiltrate in contrast to the parental progressor B16 melanoma. Immunologic analysis of tumor-bearing hosts showed variable cytotoxic T lymphocyte (CTL) responses but potent delayed-type hypersensitivity (DTH) responses directed against the melanoma cells. Fluorescent activated cell sorter (FACS) analysis of tumor-infiltrating cells from ocular tumors revealed a cellular response consisting mainly of CD8+ CTLs and macrophages. Cultured D5.1G4 melanoma cells demonstrated: 1) enhanced expression of class I major histocompatibility complex (MHC) antigens; 2) increased susceptibility to CTL-mediated killing; and 3) increased susceptibility to tumor necrosis factor (TNF)-mediated cytolysis. Therefore, the intraocular D5.1G4 mutant melanoma model provides important insights into the immunology and immunopathology of intraocular tumor rejection. More intensive analysis of this intraocular melanoma may yield strategies for directing the immune response toward tumor rejection while minimizing damage to normal ocular components.

Aqueous humor factors and their effect on the immune response in the anterior chamber

The immune response to antigens within the anterior chamber is deviant (anterior chamber associated immune deviation - ACAID) in that delayed hypersensitivity is deficient, whereas other immune effector modalities are intact. Experimental evidence indicates that the eye itself is critical to the induction of ACAID. We have examined the antigen processing and presenting potential of cells within the anterior segment of the eye, and have analyzed the potential immunoregulatory properties of these cells, their secretory products, and the aqueous humor itself. Evidence indicates that bone marrow-derived cells within the stroma of the iris and ciliary body inhibit antigen-driven T lymphocyte activation, although they themselves lack the capacity to present antigens to T lymphocytes. The mechanism is in part through secretion of immunosuppressive cytokines. Since aqueous humor contains similar cytokines, it is inferred that these molecules are constitutively secreted. We have determined that a major inhibitory molecule within normal aqueous humor is transforming growth factor-beta (TGFB), which inhibits antigen processing and presentation, and suppresses both T lymphocyte activation and certain aspects of non-specific inflammation. These effects also turn out to be properties of normal aqueous humor. These findings support the hypothesis that local features of the eye modify intraocular antigens such that an ACAID-inducing signal is produced. Experimental evidence suggests that these same properties may play a major role in suppressing efferent immune responses in the eye.

Platelets and polymorphonuclear leukocytes in experimental ocular inflammation in the rabbit eye

Accumulation of 111indium-oxine (111In)-labelled platelets and the kinetics of 111In-labelled polymorphonuclear leukocytes (PMNLs) were studied in the anterior eye during neurogenic inflammation (induced by topical neutral formaldehyde) or after paracentesis in the rabbit, after formaldehyde irritation, 40 times more platelets were found in the aqueous humor 60 min later than in the control eyes and 400 times more after paracentesis. Platelets were found to be increased in the ciliary body, but not in the iris or choroid. Under light microscopy, some of the blood vessels in the ciliary processes were occluded and filled with red blood cells and platelets. The amount of PMNLs increased in the aqueous humor 15-20 h following formaldehyde irritation. After paracentesis, increased amounts of PMNLs were found in the iris and ciliary body 3-6 h later, while in the aqueous humor PMNLs were observed already 2 h. In the present study, increased amounts of 111In-labelled platelets and PMNLs were demonstrated in the anterior eye during experimental ocular inflammation. This method provides a useful tool for evaluating the accumulation of cells or the cell kinetics in ocular tissues during experimental inflammation.

Immunohistochemical staining of the human anterior segment. Evidence that resident cells play a role in immunologic responses

We examined human corneoscleral tissue for cells that are phenotypically similar to known antigen-presenting cell (APC) populations. Antigen-presenting cells are involved in the uptake and processing of antigen for presentation to T lymphocytes, thereby playing a central role in induction of the immune response. The recognition of antigen by T lymphocytes requires that an APC express major histocompatibility complex class II molecules. Using immunoperoxidase staining techniques, the presence of cells expressing class II glycoproteins and T-cell subsets were determined. The staining patterns of the trabecular meshwork, ciliary body, cornea/sclera, and conjunctive are described for monoclonal antibodies OKT6, OKM1, HLA-DR, and HLA-DQ, and T-cell markers OKT8, Leu-3a, and Leu-4. The results of the present study demonstrate that the anterior chamber contains a network of immunocompetent cells. The presence of a subpopulation of cells within the anterior chamber that express class II glycoproteins of the major histocompatibility complex suggests this tissue may play an important role in immune regulation within the eye.

Effect of cyclosporine A on the corneal inflammatory response in herpes simplex virus keratitis

The effects of cyclosporine A (CyA), a selective inhibitor of T-lymphocyte function, on the corneal inflammatory response in herpes simplex virus (HSV) stromal keratitis was followed during the course of experimental HSV keratitis in the rabbit. The corneal response, characterized by polymorphonuclear leukocytes (PMN) and mononuclear cells, is an immunologically specific event that is dependent on the presence of viral antigens and immune cells. CyA treatment during the course of HSV keratitis resulted in a more severe and persistent stromal disease and more anterior chamber involvement than that seen in the solvent control-treated HSV-infected animals. Clinical observations correlated well with histological studies which confirmed a greater incidence of mononuclear and PMN infiltrates throughout the anterior chamber and stroma in the CyA-treated animals. HSV antigens were present in the corneas from both infected groups as observed by immunofluorescence staining, but endothelial localization of HSV antigens was seen primarily in the CyA-treated animals, often accompanied by cells in the anterior chamber. No significant differences in IgG and IgM staining in the diseased corneas and anterior chamber were noted between the CyA-treated and solvent control groups which suggests that there was no local B-cell immunosuppression.

Expression of HLA class I and II antigens on cells of the human trabecular meshwork

Human corneoscleral tissue containing trabecular meshwork and cultured human trabecular cells were examined for HLA-ABC (class I) and HLA-DR (class II) antigens of the major histocompatibility complex using an indirect immunofluorescence assay. Class I antigens were detected in the trabecular meshwork on frozen sections and on cultured trabecular cells. Class II antigens were constitutively expressed on some, but not all, cells within the trabecular meshwork. Many more cells could be induced to express class II antigens by pre-incubation in human gamma interferon. Cultured trabecular cells did not express class II antigens constitutively, but expression could be induced by gamma interferon. This study suggests that, in addition to Langerhans' cells at the limbus, other cell types within the anterior segment express major histocompatibility complex-encoded class II antigens either constitutively or inducibly. These cells may be important for the initiation and regulation of ocular immunity.