Presence of Langerhans cells in the central corneas of normal human infants.

Nine normal adult and seven normal infant human corneas were studied for the presence of dendritic epithelial Langerhans cells in a masked fashion. Epithelial flatmounts were separated from the underlying corneal stroma using EDTA. The epithelial Langerhans cell densities were determined in the limbus as well as the peripheral, pericentral, and central corneal regions following staining with ATPase. Segments of the flatmounts were also studied by immunofluorescence to confirm that the dendritic cells contained class II histocompatibility antigens. The limbus, peripheral, and pericentral zones of adult and infant flatmounts contained similar densities of Langerhans cells. However, the central corneal Langerhans cell densities in infants were significantly elevated as compared with those in adults. These results suggest that Langerhans cells are a constant constituent of the human central corneal epithelium during late gestation and early infancy. They further suggest that perturbations of the corneal epithelium are not required for the presence of Langerhans cells in the corneal epithelium.

HLA-DR+/T6- Langerhans cells of the human cornea.

We have investigated normal human corneas for the presence of T6-marker on Langerhans cells. With the exception of one pair of newborn corneas and two pairs of very young infant corneas, all HLA-DR-positive cells in central and peripheral corneal epithelium were T6-negative by double-labeled immunofluorescence. In contrast, epidermal sheets from normal human eyelid skin displayed positive staining for T6 on most of the HLA-DR-positive Langerhans cells. Since T6 antigen is considered to be a specific Langerhans cell differentiation marker, we interpret this finding to indicate a nonactivated or undifferentiated state of Langerhans cells in normal human corneas.

Phosphatic metabolites of the intact cornea by phosphorus-31 nuclear magnetic resonance.

The principal low molecular weight phosphatic metabolites of the intact cornea were identified and quantitated nondestructively by phosphorus-31 nuclear magnetic resonance (P-31 NMR) spectroscopy. As part of this analytical procedure, the intracorneal pH was approximated from the resonance shift position of inorganic orthophosphate. In addition the metabolic and pH stability of incubated corneas at 37 C in MK medium was evaluated during an 8-hr time course and compared to similar dynamic analyses performed on corneas with denuded endothelium. Perchloric acid extracts prepared from these same corneas were analyzed by P-31 NMR to verify the metabolite peak assignments and to quantitate the concentrations of minor corneal metabolites. The concentrations of phosphatic metabolites of the cornea, including three previously unidentified phosphorus-containing substances, were determined for freshly excised corneas. The initial corneal spectroscopic profile was not altered by removal of the endothelium. At 37 C the MK media-incubated intact whole corneas experienced a time-dependent decline in ATP levels with a concomitant rise in inorganic orthophosphate; however, the tissue levels of the other principal phosphatic metabolites were not altered by prolonged incubation. In contrast, removal of the endothelial layer of the cornea-induced progressive metabolic deterioration of intact corneas characterized, most prominantly, by time-dependent declines in ATP and glycerol 3-phosphorylcholine levels and concomitant increases in ADP and inorganic orthophosphate levels relative to intact whole corneas. This study has established the feasibility of monitoring the metabolic status of intact rabbit corneas nondestructively and noninvasively. As such, P-31 NMR spectroscopy offers a promising method that may enable analysis of the metabolic viability of intact human donor corneas to provide a basis for selecting donor corneas for transplantation.

Immunohistochemical localization of human tear lysozyme.

Possible local sources of human tear lysozyme were investigated using an indirect immunofluorescence technique. Lysozyme was identified in 20% to 50% of acinar and ductular epithelial cells of both main and accessory lacrimal glands. The staining was granular in character and confined to the apices of the cells. Cells that stained positive tended to be grouped. Interstitial tissues of main and accessory lacrimal tissues did not stain. Conjunctiva and all other ocular tissues examined were unstained by antilysozyme antisera. Our findings are compatible with lysozyme either being produced in lacrimal tissue or being concentrated from plasma. The absence of any other lysozyme-specific fluorescence in the interstitial elements of the lacrimal tissues supports the notion of local synthesis by acinar lacrimal tissue.

Secretory component in human ocular tissues.

Lacrimal tissue and accessory lacrimal tissue from seven autopsy cases, lacrimal tissue from three patients undergoing orbital exploration, and biopsy specimens from conjunctiva of 14 subjects were examined for the presence and distribution of secretory component by three anti-secretory-component antisera. Secretory component was present in all lacrimal and accessory lacrimal tissues but in no other ocular tissues. Over 60% of acinar cells stained for secretory component; about 5% of acinar cells stained brightly; about 30% of tubular cells stained brightly. Main and accessory lacrimal tissues appeared identical in their staining patterns. We concluded that the main sites of synthesis of secretory IgA in human ocular tissues are the lacrimal and accessory lacrimal tissues.

Lactoferrin in human ocular tissues.

The main lacrimal gland and accessory lacrimal tissue from seven autopsy cases, lacrimal biopsy specimens from three patients, and conjunctival biopsy specimens from ten patients were examined for lactoferrin by an immunohistologic technique. Lactoferrin was identified and localized to acinar epithelial cells of both main and accessory lacrimal tissue. Lactoferrin was not found in conjunctival tissue except within conjunctival neutrophils. Other possible sources of human tear lactoferrin were considered, but we concluded from our data that the primary source of lactoferrin in normal human tears is the acinar epithelium of the main and accessory lacrimal glands.

Histologic and immunohistologic comparison of main and accessory lacrimal tissue.

Main and accessory lacrimal tissues from autopsy and biopsy specimens were compared histologically and immunohistologically. Formaldehyde-fixed, paraffin-embedded specimens were studied by light microscopy with hematoxylinand-eosin and PAS staining. Glutaraldehyde-fixed, Epon-embedded specimens were sectioned at 1 micron, stained with alkaline Giemsa, and studied by light microscopy. Specimens fixed in a solution of alcohol and acetic acid were stained by immunofluorescence techniques for lactoferrin, lysozyme, secretory component, and the immunoglobulins IgG, IgA, IgM, IgD, and IgE. The main and the accessory lacrimal tissues were identical histologically and had identical distributions of secretory products and immunoglobulin-containing plasma cells. The finding of myoepithelial cells in 1-micron sections of accessory lacrimal tissue indicates autonomic innervation in that tissue. This finding, in conjunction with the identical immunohistology, indicates a common source for unstimulated and stimulated tears.

Recurrent keratoconus after keratoplasty.

A 35-year-old woman who had undergone bilateral penetrating corneal grafts for keratoconus had keratoconus in the eye that had received a graft 16 years earlier. A second penetrating keratoplasty was performed, and the excised button was examined with light and electron microscopy. Both the light and electron microscopic findings were consistent with the clinical diagnosis of keratoconus. Keratoconus in a graft for the same disease should be added to the list of late complications of successful keratoplasties.

Phlyctenular keratoconjunctivitis.

There is growing evidence that a variety of corneal disorders may be expressions of altered immune mechanisms. Phlyctenular keratoconjunctivitis is probably such a condition. Typically described as arising from hypersensitivity to tuberculin protein, other antigens clearly may participate, particularly staphylococcus products. When corneal involvement occurs, it need not be confined to the peripheral cornea. The symptoms of the process may be disproportionate to obvious findings and so exaggerated as to suggest a psychiatric disorder. Resultant visual deficits, if the disease is corneal, progressive, unrecognized, and untreated may be profound. Representative examples of this disease are cited. Immune mechanisms are reviewed. The importance of recognizing the characteristic sign and symptom complex is stressed. Appropriate diagnostic studies and treatment regimens are presented.

Immunologic defense mechanisms of the ocular surface.

The ocular surface represents an immunologic microcosm in which certain local immunologic and paraimmunologic defense systems analogous or identical to those of other mucosal surfaces are operative. These defenses include a resident normal flora; intrinsic anatomic barriers; secretion of mucous and certain chemical bacteriostatics and bacteriolytics; local humoral (slgA) antibody secretion; and local T-lymphocyte cellular responses. A series of sophisticated mechanisms has evolved to defend the ocular surface against diverse environmental pathogens. Often, the activation of one system leads to the subsequent activation of another, providing a highly integrated, series of mechanisms for host defense. And, it is clear that close integration of these various mechanisms provides a highly efficient amplification system for host defense, so that when one mechanism fails to deal with the invading pathogen the next mechanism is then efficiently initiated. Only in those situations where the pathogen overwhelms these defense systems, or is of such a persistent nature that it becomes resistant to removal by these various mechanisms, or alternatively is able to subvert its identity and, therefore, evade these mechanisms do organisms infect and cause disease. It is undoubtedly the complex interaction of all of these defense systems, both paraimmunologic and immunologic, which finally determines the integrity of the ocular surface.

Langerhans cells of the ocular surface.

Recent evidence has been collected by several investigators defining a distinct population of dendritic cells (Langerhans cells) of mesenchymal origin residing in the epidermal surfaces of many mammalian species. These cells play a dominant role in the processing of antigens presented through cutaneous surfaces and carry a Class II histocompatability antigen felt to be of central importance in the afferent arm of allograft rejection. They also possess many of the characteristics of macrophages active in the efferent arm of immunologic responses. An equivalent subset of dendritic cells (Langerhans cells) in ocular surface epithelium of the human, mouse rat, and guinea pig has been identified by enzyme histochemistry, immunofluorescence, and electron microscopy. Ocular surface Langerhans cells proliferate in the setting of corneal inflammation (remote and recent) and are depleted by topical and systemic corticosteroids. Ocular surface Langerhans cells may play a central role in ocular contact hypersensitivity, corneal allograft rejection, and ocular surface immune surveillance.