Ocular Mucosal Immunity. Handbook of Mucosal Immunology. Elsevier; 1994. pp. 569-97. [DOI: 10.1016/b978-0-12-524730-6.50052-x]

The presence of a local immune system in the upper blind and lower part of the human nasolacrimal duct

The nasolacrimal duct is exposed to exogenous agents, including potentially harmful microorganisms, coming from the eye surface by the lacrimal sac, and from the nasal cavity by the inferior meatus of the nose. The upper blind and lower part of the human nasolacrimal duct were examined immunohistochemically to ascertain the presence and localization of immunoglobulin-producing cells and the epithelial expression of IgA, IgM, and IgG in order to verify the possible antimicrobial properties of this duct. IgA-, IgM-, and IgG-positive immunocompetent cells were recognizable in the lamina propria of the upper blind and lower part of the human nasolacrimal duct, while an evident immunoreactivity for sIgA, IgM, and IgG was demonstrated in the cytoplasm of the apical epithelial cells. The results suggest that all the effector components of the mucosal immune system are present in that area of the human nasal mucosa next to the opening of the nasolacrimal duct as well as in the human lacrimal sac.

Immunoregulatory mechanisms of the eye

Immunity to protect the eye from invading pathogens is an absolute requirement for the preservation of vision. However, immune responses carry their own threat of tissue damage, due chiefly to the participation of non-specific inflammation. Because of its delicate microanatomy, the visual axis is vulnerable to distortion (and resulting blindness) from relatively trivial amounts of intraocular inflammation. Therefore, regulation of expression of immunity in the eye is critical to preservation of vision. Regulation of ocular immunity is one expression of the general phenomenon of regional immunity in which local tissue factors mold immune responses to local purposes. Ocular immune privilege is an extreme example of regional immunity. Immune privilege is an active, rather than a passive, process in which regulatory molecules and cells of the eye modulate both the induction and the expression of immunity to eye-derived antigens. Immune privilege is achieved primarily through unique features of the eye, ranging from special microanatomic factors (blood:eye barrier, absence of lymphatic draining), to soluble factors secreted by ocular cells into the ocular microenvironment, to regulatory molecules constitutively expressed on the surfaces of ocular cells. In general, the most important consequence of regulation of ocular immune responses is the virtual elimination of immunogenic inflammation from the eye. While this enables the eye to receive immune protection without the threat of blinding inflammation, it also renders the eye vulnerable to those pathogens whose elimination requires the participation of inflammatory molecules and cells.

Analysis of tear protein patterns by a neural network as a diagnostical tool for the detection of dry eyes

The electrophoretic patterns of tears from patients with dry-eye disease (n = 43) and from healthy subjects (n = 17) were analyzed by means of multivariate statistical methods and an artificial neural network (ANN), following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). From each electrophoretic pattern a data set was created, randomly divided into test (unknown samples) and training patterns (known samples), with ANN training by one of these sets. After training, the performance of the ANN was checked by presenting the test data set to the ANN. Furthermore, the data was classified using multivariate analysis of discriminance. The groups were significantly different from each other (P<0.05). The statistical procedure yielded 97% (known samples) and 71% (unknown samples) correct classifications. The ANN revealed 89% of correct classifications using the test set (unknown samples). The use of pruning algorithms (optimization procedure which automatically eliminates small weighted neurons) or genetic algorithms (optimization procedure which performs genetically induced changes of the neural net) resulted in a slight decrease of correct classifications compared to those of the nonoptimized neural network. The results reveal significant differences between the two groups. Using the ANN we were able to classify the electrophoretic tear protein pattern for diagnostic purposes.

Secretory immunoglobulin A in tears:functions and changes during contact lens wear

INTRODUCTION: Secretory immunoglobulin A (sIgA) is the predominant immunoglobulin in tears. The role of sIgA in defending the eye against pathogens has not been established clearly. There have been conflicting reports about the effect of contact lens wear on the concentration of sIgA in tears. This study was conducted to elucidate the role of sIgA in ocular defence and to determine the effect of contact lens wear on sIgA concentration. METHODS: Tears were collected from contact lens wearers and non-wearers using micro-capillary tubes. The concentration of sIgA was evaluated using an in-house ELISA. The specificity of sIgA to a strain of P. aeruginosa was examined using a fluorescent assay and the ability of neutrophils to phagocytose sIgA coated bacteria were assessed by plate counts. RESULTS: Tears contained sIgA that reacted to P. aeruginosa. P. aeruginosa coated with sIgA was phagocytosed by the neutrophils. The level of sIgA and the level of sIgA specific to P. aeruginosa in the tears of contact lens wearers were significantly reduced. CONCLUSIONS: These results indicate that contact lens wear significantly alters the level of sIgA in tears which may lead to changes in the ability of the ocular surface to defend itself against potential pathogens.

Comparative anatomy of mammalian conjunctival lymphoid tissue: a putative mucosal immune site

Organized mucosa-associated lymphoid tissue (O-MALT) is defined by mucosal lymphoid follicles with unique overlying lymphoepithelia, and classically appears in tissues with a simple columnar epithelium. Within follicle-associated epithelium, goblet cells are characteristically absent, replaced by ultrastructurally distinct antigen-absorptive cells, termed M cells (or microfold cells) for the appearance of their apical cell membranes. To determine if mammalian conjunctiva, with its stratified squamous epithelium, can be considered as a site of O-MALT, we compared the light and electron microscopic anatomy of conjunctiva from fourteen species of non-human adult mammals, and the conjunctiva of human adults harvested at autopsy. Lymphoid follicles in the conjunctiva were demonstrated in all mammals studied except for mice and rats. In those mammals with conjunctival lymphoid follicles, the follicle-associated conjunctival epithelium was notable for an absence of goblet cells. Transmission electron microscopy demonstrated an intimate association of lymphocytes with surface epithelial cells, but epithelial cell morphology was uniform overlying the follicle, and other ultrastructural features of M cells were absent. Therefore, conjunctival lymphoid follicle-associated stratified squamous epithelium demonstrates some but not all features of O-MALT lymphoepithelia. Further studies are necessary to determine what role conjunctival lymphoid tissue may play in mucosal immunity.

Anatomy of mammalian conjunctival lymphoepithelium

Ocular surface immune mechanisms are subservient to the fine function of the eye. A clear cornea with a smooth, well-lubricated facade is prerequisite to lucid vision. Hence, corneal inflammation and post-inflammatory scarring are intolerable, and the cornea contains a minimum of lymphoid elements. Although conjunctival dysfunction and consequent tear film deficiency can malign the corneal surface, conjunctival inflammation is tolerated to a considerable degree. In contrast to the human cornea, human conjunctiva contains an abundance of lymphoid tissue. Certain aspects of human conjunctival immunology elicit little debate. Langerhans cells are abundant in conjunctival epithelium. Isolated CD8+ suppressor/cytotoxic T cells predominate in conjunctival epithelium, while T cells in the substantia propria distribute equally between CD4+ T helper cells and CD8+ cells. Yet the presence of plasma cells in human conjunctiva, the expression of secretory component by human conjunctival epithelium, and the function of human conjunctival lymphoid follicles are in dispute. Confusion may derive in part from the use of inappropriate animal models; rodent conjunctiva does not appear to be a worthy facsimile for human conjunctiva. Discrepancies between different human studies likely result from variance in subject age, biopsy site and extent, histologic or histochemical technique, and perhaps the degree of inflammation present at the time of biopsy. Careful immunohistochemical and in situ molecular assays on well-defined loci within the conjunctiva of comparable human subjects may resolve such questions in the future. Organized mucosa-associated lymphoid tissue is rigorously defined as mucosal lymphoid follicles with an ultrastructurally distinct overlying lymphoepithelium. Based on available evidence, the epithelium overlying mammalian conjunctival lymphoid follicles does not contain distinct M cells. Whether zonal differences in morphology reflect real differences in the capacity to sample tear film antigens for presentation to the mucosal immune system remains to be established.

Effect of tear secretory IgA on chemotaxis of polymorphonuclear leucocytes

PURPOSE

The aim of the present study was to examine the effect of tear and purified colostrum secretory IgA (sIgA) on polymorphonuclear leucocyte (PMN) chemotaxis.

METHODS

The chemotactic effect of tear and purified sIgA for PMN was studied using a modified Boyden chamber. Tears treated with anti-human IgA, complement-inactivated tears and albumin were used as controls.

RESULTS

The data indicate that both tear and purified sIgA are highly chemotactic for PMN. Anti-sIgA antibodies reduced the chemotactic effect of closed-eye tears (34%) and tear collected during ocular inflammation.

CONCLUSION

The massive recruitment of PMN in tears during sleep may be partially attributed to the increased levels of tear sIgA. This may play an important role in protecting the eye against bacterial infection.

Effect of sialodacryoadenitis virus exposure on acinar epithelial cells from the rat lacrimal gland

Sialodacryoadenitis virus (SDAV), a RNA coronavirus, induces degenerative, necrotic and atrophic alterations in acinar epithelial cells of the rat lacrimal gland. To begin to explore the underlying mechanism(s) of this viral effect, we sought in the present study to: (1) determine whether SDAV invades and replicates in lacrimal gland acinar cells in vitro and (2) assess whether short-term SDAV challenge interferes with the viability or function of acinar cells in vitro. For comparison we also evaluated the relative infectivity of SDAV in acinar epithelial cells from lacrimal, submandibular and parotid glands, given that salivary tissues are known to be highly susceptible to SDAV infection in vivo. Acinar epithelial cells from lacrimal, submandibular or parotid glands were isolated from male rats, exposed briefly to SDAV or control cell antigen and then cultured for four, eight or twelve days. At experimental termination, SDAV titers in both media and sonicated cell extracts were evaluated by plaque assay titration on mouse L2 cell monolayers. To evaluate functional aspects of lacrimal gland acinar cells, SDAV-infected cells were incubated in the presence or absence of dihydrotestosterone and culture media were analyzed by RIA to measure the extent of the androgen-induced increase in secretory component (SC) production. Our results showed that: (1) SDAV invades and replicates in lacrimal gland acinar cells, Viral challenge resulted in a significant, time-dependent increase in SDAV titers, that were primarily cell-associated and greatly exceeded amounts contained in the original inoculum; (2) SDAV infection did not compromise lacrimal acinar cell viability or prevent the cellular SC response to androgens. Viral presence, though, did often attenuate the magnitude of this hormone action; and (3) SDAV infects salivary acinar cells, but the kinetics and magnitude or viral replication in lacrimal, submandibular and parotid cells showed considerable variations. These findings demonstrate that SDAV invades and replicates in acinar epithelial cells from lacrimal and salivary glands. The resulting release of infectious progeny may play a role in the SDAV-induced pathology of exocrine tissues in vivo.

Identification and endocrine control of sex steroid binding sites in the lacrimal gland

Previous research has indicated that the lacrimal gland may be a target organ for sex steroids and that androgen effects on this tissue may be inhibited by pituitary deficiency or diabetes. To extend these findings, the objectives of the current investigation were 3-fold: [a] to determine whether specific and high-affinity binding sites for androgens and estrogens exist in rat lacrimal tissue; [b] to assess whether the number and affinity of androgen binding sites in the lacrimal gland may be influenced by hypophysectomy or acute diabetes; and [c] to examine whether androgen receptor mRNA may be detected in lacrimal tissues of a variety of species. Following the collection of lacrimal gland samples, tissues were processed for the conduct of equilibrium binding methods or molecular biological techniques. Our results demonstrated that a single class of saturable, high-affinity and stereochemically selective binding sites for androgens exist in lacrimal tissues of male and female rats. These sites possessed a dissociation constant of approximately 1 nM and were also present in isolated acinar epithelial cells. In contrast, we were unable to find any evidence for the presence of specific or high-affinity receptors for estrogens in the rat lacrimal gland. With regard to changes in the endocrine environment, hypophysectomy led to an increase in the number and affinity of androgen binding sites in rat lacrimal tissue cytosol, whereas diabetes reduced the total quantity of these sites. Of interest, androgen receptor mRNA was detected in lacrimal glands of mice, rats, hamsters, guinea pigs, rabbits and humans. Overall, our findings show that the lacrimal gland is a target organ for androgens and that androgen action in this tissue may be mediated through an interaction with specific and high-affinity binding sites.