Do we really need cadavers anymore to learn anatomy in undergraduate medicine?

With the availability of numerous adjuncts or alternatives to learning anatomy other than cadavers (medical imaging, models, body painting, interactive media, virtual reality) and the costs of maintaining cadaver laboratories, it was considered timely to have a mature debate about the need for cadavers in the teaching of undergraduate medicine. This may be particularly pertinent given the exponential growth in medical knowledge in other disciplines, which gives them valid justification for time in already busy medical curricula. In this symposium, the pros and cons of cadaver use in modern medical curricula were debated and audience participation encouraged.

Analysis of the cellular infiltrate in the iris during experimental autoimmune encephalomyelitis

PURPOSE

Previous studies have shown that experimental autoimmune encephalomyelitis (EAE) and anterior uveitis (AU) develop in Lewis rats immunized with myelin basic protein (MBP). The purpose of this study was to characterize the dynamics, distribution, and phenotype of infiltrating cells in the iris during EAE-associated AU.

METHODS

Lewis rats were immunized with MBP emulsified in complete Freund's adjuvant (CFA) or with CFA alone. Cellular infiltration of the iris was analyzed at various time points by immunohistochemistry of wholemounts, flow cytometry, and immunoelectron microscopy, by using monoclonal antibodies specific for monocytes/macrophages (ED1), T lymphocytes (R73, W3.25, OX8), T-cell activation markers (OX39, OX40), granulocytes (HIS48), major histocompatibility complex (MHC) class II (OX6), and neurofilament (2H3).

RESULTS

MBP-immunized rats showed development of characteristic monophasic EAE, followed, after resolution of paralysis, by mild self-limited AU. Initially, focal infiltrates of round MHC class II(+) and ED1(+) cells were found in the iris. During the course of AU, the midiris became massively infiltrated with ED1(+) monocytes-macrophages, R73(+) T cells, granulocytes (HIS48(+)), and MHC class II(+) cells. The influx of T cells consisted of CD4(+) and CD8(+) cells, of which only a small fraction (<14 and 11%, respectively) expressed activation markers. The infiltrating cells accumulated in proximity to myelinated and nonmyelinated nerve bundles and in the vicinity of blood vessels in the iris. No evidence was found for demyelination or nerve degradation. Neither EAE nor AU developed in CFA-treated control rats.

CONCLUSIONS

These data show that EAE-associated AU is characterized by a transient mixed cellular infiltrate consisting of monocytes-macrophages, granulocytes, and CD4 and CD8 T cells. The preferential accumulation of inflammatory cells in the vicinity of nerve fibers suggests that AU in this model may result from autoreactivity to nerve antigens.

Optimal methods for preparation and immunostaining of iris, ciliary body, and choroidal wholemounts

PURPOSE

Investigations into the biology of resident and infiltrating immune cells in the uveal tract of the rodent eye have been greatly aided by the use of tissue wholemount methods. These methods offer a number of advantages over conventional histological and frozen section techniques. The purpose of this article is to provide a detailed step by step guide to aid others who may wish to use this method.

METHODS

A detailed description of whole-body perfusion fixation, dissection and isolation of the iris-ciliary body from the anterior segment and the choroid from the posterior segment is provided. In addition, the techniques used to handle whole tissue pieces during single and double immunohistochemical staining protocols, as well as the staining protocols themselves, are described.

RESULTS

In refining the techniques described, the author has catalogued a number of frequent problems which compromise immunohistochemical staining results. A troubleshooting guide aimed to help identify the cause of common problems and with some suggested remedies is provided.

CONCLUSIONS

Although tissue wholemounts are frequently used in retinal research, a similar approach to investigating the components of the uveal tract has only recently been applied. The methods described in this article will provide sufficient detail for other investigators to obtain maximum benefit from this alternative approach and provide an additional technique to assist in their investigations of ocular immunobiology.

Resident tissue macrophages within the normal rat iris lack immunosuppressive activity and are effective antigen-presenting cells

Despite extensive study of the numerous immunoregulatory mechanisms that contribute to the 'immune-privileged'nature of the anterior chamber (AC) of the eye, little is known of the functional nature of antigen-presenting cells (APC) present in the tissues adjoining the AC. In the present study, we have compared the antigen-presenting capacity of dendritic cells (DC) and macrophages isolated from the normal rat iris. Whereas iris DC exhibited a potent ability to stimulate resting allogeneic T cells in MLR cultures (an in-vitro correlate of the ability to induce primary T cell responses), resident iris macrophages displayed negligible MLR-stimulatory capacity. Significantly, iris macrophages could efficiently elicit proliferation of primed antigen-specific T cells (an in-vitro correlate of the ability to act as local APC in secondary responses). This antigen-presenting activity was approximately half that of fully 'mature' iris DC and considerably greater than that of freshly isolated iris DC. A key contributor to the effectiveness of resident iris macrophage antigen presentation was considered to be the absence of lymphocytostatic control of T cell proliferation exerted by these cells. The results indicate dichotomous but complementary roles for DC (immune surveillance) and macrophages (local antigen presentation in secondary responses) in this tissue.

Environmental scanning electron microscopic study of macrophages associated with the tunica vasculosa lentis in the developing rat eye

AIMS

To demonstrate the value of environmental scanning electron microscopy (ESEM) when used in combination with immunogold/silver enhancement methods as a valuable tool in ocular research, and to determine the phenotype of macrophages associated with the tunica vasculosa lentis while maintaining a topographical view of the lens surface.

METHODS

Prenatal and postnatal rat eyes were investigated by conventional scanning electron microscopy and ESEM. In the latter case tissues were prestained with a panel of antileucocyte monoclonal antibodies and visualised with colloidal gold conjugated secondary antibody followed by silver enhancement.

RESULTS

The preliminary data demonstrate that ED1(+) ED2(+) macrophages occur in large numbers around the lens and are associated with sectors of both normal vessels and those undergoing regression.

CONCLUSION

The present study demonstrates that ESEM is an ideal way to combine scanning electron microscopy with immunohistochemistry and is therefore likely to have multiple other applications in ocular research.

Subretinal macrophages in the developing eye of eutherian mammals and marsupials

Blood-borne mononuclear cells invade the developing retina via the hyaloid vasculature at the optic nerve head. Following removal of apoptotic cell debris they give rise to the network of resident microglia. The population of cells recently described in the peripheral subretinal space of developing human eyes may represent a further population of macrophages destined to become microglia. The aim of the present study was to confirm the presence of subretinal macrophages in the developing eye in other mammalian species and perform preliminary immunophenotypic analysis in rat tissues. The range of species chosen included eutherian mammals (rat and rabbit) and marsupials (wallaby and opossum). Ocular tissues from a range of developmental stages were studied by scanning electron microscopy and transmission electron microscopy. Distinctive networks of dendriform and pleomorphic macrophages were observed by scanning electron microscopy in the peripheral subretinal space of D2 rabbits, newborn and D2 rats and D75 wallaby. Transmission electron microscopic studies of D2 rabbit, newborn and D2 rat and all ages of North American opossum revealed cells with the ultrastructural features of macrophages in the peripheral subretinal space, cilio-retinal junction and between ciliary epithelial cells. Preliminary immunoperoxidase studies using a panel of anti-leukocyte monoclonal antibodies on frozen sections of rat ocular tissues (newborn, D2 and D4) revealed ED1(+) Ox42(+) ED2(+) but Ox6(-) cells in the peripheral subretinal space, peripheral retina and ciliary body epithelia. The data confirms that subretinal macrophages are a feature of the developing eye in a broad range of mammalian species and immunophenotypic evidence leads the author to postulate that these cells arise from the ciliary body vasculature and may migrate into peripheral neural retina and mature into resident microglia.

Dendritic cells and macrophages in the uveal tract of the normal mouse eye

BACKGROUND/AIMS

Dendritic cells (DC) and macrophages are components of the immune cell populations in the uveal tract whose density, distribution, turnover, and function may play a role in the maintenance of immunological homeostasis in the eye. Little is known of these cells in the mouse eye despite this being the predominant experimental model in many studies of ocular immune responses and immunoinflammatory mediated eye diseases. The aim of the present study was to obtain further immunophenotypic data on resident tissue macrophages and DC populations in the mouse uveal tract.

METHODS

Pieces of iris, ciliary body, and choroid dissected from perfusion fixed BALB/c mice were incubated whole in a variety of anti-macrophage and DC monoclonal antibodies (mAbs). Labelled cells were visualised using either single or double immunoperoxidase techniques.

RESULTS

Quantitative analysis and double immunolabelling revealed that 80% of F4/80(+) cells (a mAb that recognises both DC and macrophages) in the iris are macrophages (SER4(+)). The iris contained a network of Ia+ cells (412 (SD 130) cells/mm2) of which two thirds appear to be DC. A similar pattern was observed in the ciliary body and choroid. Only a few DC in the uveal tract were very weakly reactive for mAbs which recognise B7-1 (CD80), B7-2 (CD86), beta2 integrin (mAb N418), and multivesicular bodies associated with antigen presentation (mAb M342).

CONCLUSIONS

The present study reveals that the mouse uveal tract, like the rat, contains rich networks of DC and resident tissue macrophages. The networks of resident tissue macrophages in the mouse uveal tract closely resemble similar networks in non-ocular tissues. The phenotype of uveal tract DC suggests they are in the "immature" phase of their life cycle, similar to Langerhans cells of the skin, thus implying their role in situ within the eye is antigen capture and not antigen presentation.

Distribution and phenotype of dendritic cells and resident tissue macrophages in the dura mater, leptomeninges, and choroid plexus of the rat brain as demonstrated in wholemount preparations

Dendritic cells (DC) are regarded as the 'sentinels' of the immune system. They play a crucial role in surveillance of peripheral tissues, trapping antigens encountered there, and migrating via the lymphatics to lymphoid organs where they interact with naive T cells thus generating antigen-specific primary immune responses. Until now it has been assumed DC are largely absent from the brain, meninges, and the choroid plexus within the ventricles. Such a situation was thought to partly explain the 'immune privileged' nature of the central nervous system (CNS). The present study of normal rat tissues using single and double immunohistochemistry reveals for the first time that extensive networks of major histocompatability (MHC) class II+/OX62+ DC are widely distributed in sites which may potentially encounter CNS antigens. These sites included the dura mater, leptomeninges, and the choroid plexus. These putative DC were negative when stained with the anti-resident tissue macrophage monoclonal antibody ED2. In addition to the rich networks of DC, dense populations of resident tissue macrophages (ED2+ and ED1+) were also demonstrated in the dura mater, leptomeninges and to a lesser extent in the choroid plexus. The presence of rich networks of DC and macrophages in the vascular and supporting tissues of the brain may play an important role in inflammatory and immune-mediated disorders affecting the CNS, including auto-immune demyelinating diseases such as multiple sclerosis.

The distribution of immune cells in the uveal tract of the normal eye

Inflammatory and immune-mediated diseases of the eye are not purely the consequence of infiltrating inflammatory cells but may be initiated or propagated by immune cells which are resident or trafficking through the normal eye. The uveal tract in particular is the major site of many such cells, including resident tissue macrophages, dendritic cells and mast cells. This review considers the distribution and location of these and other cells in the iris, ciliary body and choroid in the normal eye. The uveal tract contains rich networks of both resident macrophages and MHC class II+ dendritic cells. The latter appear strategically located to act as sentinels for capturing and sampling blood-borne and intraocular antigens. Large numbers of mast cells are present in the choroid of most species but are virtually absent from the anterior uvea in many laboratory animals; however, the human iris does contain mast cells. Small numbers of what are presumed to be trafficking lymphocytes are present in the uveal tract of normal eyes. There is little data available on the presence or absence of eosinophils. The role of these various cell types in immune homeostasis and ocular inflammation is briefly considered.

Resident and infiltrating cells in the rat iris during the early stages of experimental melanin protein-induced uveitis (EMIU)

Experimental melanin protein-induced uveitis (EMIU) is reported to be a model of anterior uveitis and choroiditis in which the retina is spared. In this study, we chose to compare EMIU with experimental autoimmune uveoretinitis (EAU), a well-recognised model of endogenous posterior uveitis, with regard to the nature and dynamics of the cellular infiltrate in the iris. Female Lewis albino rats were immunised with mixtures of crude retinal extract/complete Freund's adjuvant (CFA) (EAU), phosphate-buffered saline/CFA (controls), or iris melanin/CFA (EMIU) using established protocols. Animals were sacrificed on days 10 and 13 (around disease onset). Following whole body perfusion fixation, irides were dissected from the remainder of the globe. Iris wholemount preparations were then subjected to immunohistochemical analysis in order to investigate both the dynamics of infiltrating leukocytes and the effects of the inflammatory changes on resident immune cells in the iris. The nature of the cellular infiltrate in both EMIU and EAU models was essentially similar, namely there was a rich infiltrate of EDI+ mononuclear cells, Ox42+ neutrophils and T cells. Resident tissue macrophages (ED2+) were slightly below normal densities in the iris of EAU animals and marginally elevated in EMIU animals, MHC class II (Ia) staining, associated in the normal eye with dendritic cells (DC), was considerably elevated in EMIU. It is likely that this was due to both increased DC numbers and an influx of Ia+ exudate macrophages. No striking difference was found in the nature and phenotype of the cellular infiltrate in the iris at the onset of the disease in these two models of uveitis (EAU and EMIU). This suggests that the anterior segment inflammation in both models represents non-specific changes secondary to cytokine release associated with interaction of activated antigen-specific T cells and target antigens, namely retinal photoreceptors in EAU and uveal tract melanin-containing cells in EMIU. Alternatively, it may suggest that antigen-presenting cells resident in the iris and ciliary body in normal eyes have access to ocular antigens on both sides of the blood-ocular barrier and are capable of activating circulating antigen-specific T cells in these models.

Major histocompatibility complex (MHC) class II--positive dendritic cells in the rat iris. In situ development from MHC class II-negative precursors

PURPOSE

To examine the postnatal development of major histocompatibility complex (MHC) class II-positive dendritic cells (DC) in the iris of the normal rat eye.

METHODS

Single- and double-color immunomorphologic studies were performed on whole mounts prepared from rat iris taken at selected postnatal ages (2 to 3 days to 78 weeks). Immunopositive cells were enumerated, using a quantitative light microscope, and MHC class II expression on individual cells was assessed by microdensitometric analysis.

RESULTS

Major histocompatibility class II-positive DCs in the iris developed in an age-dependent manner and reached adult-equivalent density and structure at approximately 10 weeks of age, considerably later than previously described in other DC populations in the rat. In contrast, the anti-rat DC monoclonal antibody OX62 revealed a population of cells present at adult-equivalent levels as early as 3 weeks after birth. Dual-color immunostaining and microdensitometric analysis demonstrated that during postnatal growth, development of the network of MHC class II-positive DCs was a consequence of the progressive increase in expression of MHC class II antigen by OX62-positive cells.

CONCLUSIONS

During postnatal growth, the DC population of the iris develops initially as an OX62-positive-MHC class II-negative population, which then develops increasing MHC class II expression in situ and finally resembles classic DC populations in other tissue sites. Maturation of the iris DC population is temporally delayed compared with time to maturation in other tissue sites in the rat.

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.

Macrophages and dendritic cells in normal and regenerating murine skeletal muscle

Mononuclear phagocytes and MHC class II+ dendritic cells (DC) were identified in frozen sections of skeletal muscle using a panel of pan-specific antimacrophage (MOMA-2, SER-4, Mac-1, F4/80), anti-major histocompatibility complex (MHC) class II (M5/114) and anti-DC (NLDC-145, N418, M342) monoclonal antibodies. Uninjured and regenerating skeletal muscle were investigated in SJL/J and BALB/c mice, strains with known differences in muscle regenerative capacity. Resident tissue macrophages and MHC class II+ DC were present within uninjured mouse muscle. A subpopulation of DC were positive for the pan-DC markers, N418 and M342, and negative for the lymphoid DC marker NLDC-145. Following crush injury, the macrophage population increased by day 2, became marked by day 3, and had decreased by day 6. In contrast, the number of MHC class II+ cells around the injury site increased steadily after injury and remained high at day 6. The numbers of macrophages and DC detected by immunohistochemical staining were consistently higher in SJL/J than BALB/c muscles. This study confirms that macrophages are a significant component of normal murine skeletal muscle and that these cells increase dramatically after injury. Furthermore the data also reveal for the first time that DC are present in normal skeletal muscle and that MHC class II+ cells, including DC, increase after injury. The presence of DC in muscle has important implications for the understanding of the immunobiology of muscle and immune-mediated processes such as the host versus graft responses following muscle transplants and autoimmune diseases affecting this tissue.

Resident and infiltrating immune cells in the uveal tract in the early and late stages of experimental autoimmune uveoretinitis

PURPOSE

To investigate the dynamics of resident and infiltrating immune cells in the choroid and iris during the early and late stages of experimental autoimmune uveitis (EAU) in Lewis rats.

METHODS

Uveoretinitis was induced by footpad injection of crude retinal extract and complete Freund's adjuvant with concurrent intraperitoneal injection of Bordetella pertussis. Five experimental (EAU) and five control animals (adjuvant alone) were studied at days 5, 7, 9, 11 (prodromal stage) and 42 (late stage) after immunization. Five normal animals and five animals injected with B. pertussis alone served as further controls. Immunohistochemical localization of resident macrophages, major histocompatibility complex class II (Ia)+ dendritic cells (DC), infiltrating mononuclear cells, and T cells was performed on wholemounts of isolated choroidal and iris tissue.

RESULTS

Double immunolabeling confirmed the presence of distinct networks of macrophages (591 +/- 52 cells/mm2) and DC (746 +/- 38 cells/mm2) in the rat choroid. No marked qualitative and quantitative changes were observed in the density or morphologic appearance of ED2+ resident tissue macrophages in the choroid and iris before clinical onset of ocular disease. On day 11, infiltration of ED1+ monocytes had occurred in the iris but not in the choroid; however, marked infiltration of T cells was evident in both choroid (286 +/- 161 cells/mm2) and iris (196 +/- 72 cells/mm2). The total density of Ia+ cells was significantly elevated in the choroid (1152 +/- 192 cells/mm2) at day 11, and small, round Ia+ cells were two to three times more frequent than normal at both sites. The density of T cells and Ia+ cells remained significantly elevated in the choroid and iris in the late stages of EAU.

CONCLUSIONS

These data suggest resident uveal tract macrophages undergo no significant alteration in density in the early stages of EAU and that the earliest site of mononuclear cellular infiltrate in EAU occurs in the iris. The increased total density of Ia+ cells in the choroid on day 11 and the presence of significantly increased numbers of small, round Ia+ cells in the iris and choroid may represent increased trafficking of DC in the eye during uveoretinitis. Furthermore, the raised numbers of Ia+ cells, concurrent with the influx of T cells, suggests Ia+ DC and macrophages may act as local antigen-presenting cells in the induction of uveoretinitis.

Origin and steady-state turnover of major histocompatibility complex class II-positive dendritic cells and resident-tissue macrophages in the iris of the rat eye

Recent studies have identified distinct but co-existing networks of resident tissue macrophages and MHC class II-positive DC present in tissues bordering the anterior chamber of the eye, a site classically regarded as 'immune-privileged'. As the DC network, present at approximately 500 cells/mm2, accounts for virtually all MHC class II immunostaining in these tissues and possesses potent capacity to stimulate primary allogenic responses in vitro, it is proposed that these cells may play an important role in immune surveillance of the anterior chamber. Tissue macrophage and DC population kinetics in the iris were examined by using X-irradiation exposure to interrupt the steady-state renewal of these cells by haematopoietically derived precursors. MHC class II-positive iris DC exhibited a half-life of approximately 3 days, a rapid turnover rate which closely resembled that of DC present in mucosal epithelia. In contrast, the resident tissue macrophage population displayed a considerably slower turnover (half-life of 10-12 days) comparable to that of epidermal Langerhans cells in the present study. Bone marrow transplantation studies confirmed the haematopoietic origin of the iris DC population. The present study provides the first estimates of the steady-state population kinetics of antigen-presenting cell populations in the iris and has important implications for understanding the role of these cells in immunological homeostasis of the anterior chamber.

Immunomorphologic studies of mast cell heterogeneity, location, and distribution in the rat conjunctiva

Mast cells are crucial components of immediate and some delayed-type hypersensitivity reactions. They play a pivotal role in allergic conjunctivitis and other immunoinflammatory disorders of the ocular surface, yet little is known of their distribution and heterogeneity in the conjunctiva of potential animal models, such as the rat. In this study, mast cell types were investigated in histologic sections and corneal-conjunctival-lid whole mounts by using toluidine blue, alcian blue-safranin, and immunohistochemical staining methods (anti-rat mast cell proteinase [RMCP] antibodies). Quantitative analyses were performed on corneal-conjunctival-lid whole mounts by using the optical dissector procedure to obtain the density of mast cells per unit volume in different regions of the conjunctiva. Single and double immunohistochemical analyses revealed that the mast cells in the conjunctiva of the limbus, fornices, and lid margin were strongly RMCP I+, suggesting that they were of the connective tissue phenotype. Mast cells containing the mucosal mast cell proteinase RMCP II were not present in the normal conjunctiva. Histochemical analysis revealed that the maturity of the connective tissue mast cells, as assessed by the presence or absence of safranin (heparin)-positive granules in their cytoplasm varied in different regions. In the lid margin 60% to 78% of the mast cells were solely alcian blue-positive, whereas in the fornices 68% to 78% were safranin-positive. In the limbus the predominant type of mast cell was either safranin-positive or contained mixed granules. Mast cell densities were greatest close to the lid margin (10,000 to 12,000 cells/mm3), followed by the limbus (3400 to 4800 cells/mm3) and were rare in the remainder of the conjunctiva (500 to 1000 cells/mm3), with the exception of the region around the nictitating membrane. This study of rat conjunctival mast cells provides essential baseline data for future studies of the role of mast cells in models of allergic conjunctivitis.

Inhibition of tumor necrosis factor activity minimizes target organ damage in experimental autoimmune uveoretinitis despite quantitatively normal activated T cell traffic to the retina

Recent studies demonstrated that administration of a p55-tumor necrosis factor (TNF) receptor IgG-fusion protein (TNFR-IgG) prevented the clinical onset of experimental autoimmune encephalomyelitis but did not alter the number or tissue distribution of autoantigen-specific CD4+ effector T cells which trafficked into the central nervous system. To determine whether specific target tissues of autoimmune damage remain intact after TNFR-IgG treatment despite the presence of inflammatory cells within the tissues, we examined rats with experimental autoimmune uveoretinitis (EAU), as in this model, the main target of autoreactive CD4+ T cells, the retinal rod outer segments (ROS), can be examined readily by light microscopy. As judged by direct ophthalmoscopy, the onset of inflammation in the anterior chamber of the eye in EAU following administration of TNFR-IgG was delayed by 6 days compared to untreated controls, but the magnitude of the response was only slightly less than controls. Histological examination of the retinae and direct assessment of retinal inflammation revealed a disproportionate sparing of ROS in the TNFR-IgG-treated animals despite a level of retinal inflammation not substantially less than controls in which ROS damage was marked. Analysis of retinal leukocytes by immunofluorescence microscopy and flow cytometry indicated that approximately equal numbers of CD4+ alpha beta TCR+ lymphocytes were present in treated and control retinae, more than 30% of CD4+ cells in both experimental groups expressed the CD25 or MRC OX40 activation markers and most cells, which would include the CD4+ T lymphocytes, were activated as evidenced by MHC class II expression. Fewer activated macrophages and granulocytes were present in the treated retinae, possibly reflecting the lower level of tissue damage and subsequent accumulation of these inflammatory cells. The results demonstrate directly that a tissue specifically targeted for autoimmune destruction can be protected despite the influx of fully activated CD4+ T cells.

Endotoxin-induced uveitis. Kinetics and phenotype of the inflammatory cell infiltrate and the response of the resident tissue macrophages and dendritic cells in the iris and ciliary body

PURPOSE

Footpad injection of bacterial lipopolysaccharide (LPS) causes pronounced anterior uveitis in susceptible species and strains. Recent studies using wholemount techniques have demonstrated the presence of rich networks of major histocompatibility complex (MHC) class II-positive dendritic cells (DC) and resident tissue macrophages in the iris and ciliary body. The aim of this investigation was to determine the immunophenotype and dynamics of the inflammatory cell infiltrate during LPS-induced anterior uveitis using the wholemount method and to examine the response of the resident tissue macrophages and DC to an acute inflammatory episode in the anterior segment.

METHODS

Female Lewis rats (8 to 12 weeks old, n = 49) received a single footpad injection of 100 micrograms of LPS and were killed at various times up to 6 weeks after injection. The iris-ciliary body complex from each eye was removed intact and subdivided into segments and immunostained using a panel of monoclonal antibodies to a variety of immune cell types.

RESULTS

The wholemount method clearly illustrates that during endotoxin-induced uveitis (EIU), the earliest cellular infiltrate includes small, round ED1+ mononuclear cells marginating in the iris vasculature approximately 2 hours after injection. Marginating Ox42+ polymorphonuclear leukocytes were detectable in the iris vessels approximately 4 to 6 hours after injection and were especially numerous in the ciliary body base approximately 24 hours after injection. The overall density of resident tissue macrophages (ED2+) remained largely unchanged in the course of EIU. In contrast, the total number of MHC class II-bearing (Ox6+) cells (putative dendritic cells) increased 30% in the first 6 hours and 200% by 72 hours. During the acute phase of the inflammatory response (up to 24 hours), the proportion of these cells with a dendritiform morphology decreased (93% to 50%). The number of T cells showed a biphasic response peaking at 4 to 6 hours and again at 24 hours (290 cells/mm2); however, their numbers had resumed normal low density (4 cells/mm2 to 25 cells/mm2) by 6 weeks.

CONCLUSIONS

The results suggest that the neutrophilic infiltration in EIU occurs predominantly in the base of the ciliary body, whereas the monocytic and lymphocytic infiltrate occurs in the iris vasculature. Resident tissue macrophages do not undergo marked changes in density or morphology in the early course of the disease. Recruitment of T cells into the anterior segment in EIU may suggest a previously unsuspected role for these cells in the immunopathology of this disease. Changes in density and morphology of MHC class II+ DC in the iris, which persisted for at least 6 weeks, were interpreted as an increase in recruitment and migration of these cells that may serve to enhance the efficiency of immune surveillance in the anterior segment at crucial times of bacterial infection.

Functional studies of major histocompatibility class II-positive dendritic cells and resident tissue macrophages isolated from the rat iris

Recent immunomorphological studies have demonstrated the presence of distinct populations of resident tissue macrophages and major histocompatibility complex (MHC) class II+ dendritic cells within tissues lining the anterior chamber of rat, mouse and human eyes. The location of these cells in sites of potential contact with the aqueous humour-filled anterior chamber suggests that either of these cells may perform a role in immunosurveillance of this 'immune-privileged site'. The aim of the present study was to isolate highly purified dendritic cells and tissue macrophages from enzymatically disaggregated rat irides and to compare their relative capacity to stimulate unprimed T lymphocytes in vitro in a mixed leucocyte reaction assay. Dendritic cells freshly isolated from iris tissue exhibited a moderate ability to stimulate unprimed T lymphocytes. However, following 48 hr of culture in granulocyte-macrophage colony-stimulating factor (GM-CSF)-supplemented medium, MHC class II+ dendritic cells demonstrated a markedly enhanced stimulatory capacity that was identical to that of Langerhans' cells isolated from skin. Tissue macrophages isolated from rat iris, however, demonstrated little allostimulatory capacity, either when freshly isolated or following 48 hr of culture in GM-CSF. This study provides the first definitive evidence that MHC class II+ cells within tissues lining the anterior chamber are functionally equivalent to dendritic cells described in other tissues. These findings have important implications for our understanding of the mechanisms of immune surveillance within the anterior chamber of the eye.

Precautionary note on retrobulbar alcohol injections

Images

Immunomorphologic studies of macrophages and MHC class II-positive dendritic cells in the iris and ciliary body of the rat, mouse, and human eye

PURPOSE

To establish the presence of distinct populations of macrophages and MHC class II (Ia)-positive dendritic cells (DC) in the iris and ciliary body of the rat, mouse, and human eye.

METHODS

Iris-ciliary body wholemounts from a variety of rat strains, balb/c mice, and human eyes were investigated by single and double immunohistochemistry, immunoelectron microscopy, and confocal microscopy to determine the phenotype, density, distribution, and location of macrophage and DC populations.

RESULTS

Dendritiform and pleiomorphic macrophages were distributed in a regular array within the rat iris and ciliary body stroma (600 to 700 cells/mm2 or 7000 cells per iris). Ia+ DC were distributed in a similar regular network (400 cells/mm2 or 5500 cells per iris) within the iris stroma and ciliary epithelium. In the rat, a strain-dependent variation in the numbers of DC was noted, F344 rats displaying highest numbers of DC (962 +/- 398 cells/mm2) and WAG strain the lowest numbers (285 +/- 218 cells/mm2). Double color immunoperoxidase staining using anti-Ia and anti-pan specific macrophage monoclonal antibodies revealed that macrophages and Ia+ DC are distinct populations with only 5% to 15% overlap. Single immunoperoxidase of mouse iris and ciliary body using anti-pan macrophage and anti-Ia antibodies produced findings identical to those in rat. Preliminary studies of human tissue using confocal microscopy of immunostained whole irides also revealed a regular array of macrophages and MHC class II (HLA-DR)+ dendritiform cells.

CONCLUSIONS

The mammalian iris contains rich networks of dendritiform-pleiomorphic macrophages and MHC class II+ DC. These findings suggest that the DC in the tissues lining the anterior chamber represent a rich network of putative antigen presenting cells and are the most likely candidates for transmitting antigen-specific signals from the anterior chamber in vivo and in experimental models such as ACAID: These observations have wide implications for the understanding of the pathogenesis of anterior and posterior uveitis.

Distribution and characterisation of rat choroidal mast cells

Despite the implication that choroidal mast cells are involved in the onset of experimental autoimmune uveoretinitis (EAU), a widely used animal model of uveoretinitis, little is known of these cells. In the present study the distribution, total number, regional density, and phenotype of choroidal mast cells were examined in Lewis, Wistar Furth, PVG/c, and brown Norway rats. Choroidal mast cells were predominantly associated with arteries and arterioles of more than 30 microns diameter which lie in the outer (sclerad) choroid. The density of mast cells was greatest in the posterior choroid with density diminishing anteriorly. The choroid of male Lewis rats contained significantly greater number of mast cells than that of females (p < 0.01). Histochemical (Alcian blue/safranin) and immunohistochemical (anti-rat mast cell protease I and II monoclonal antibodies) studies revealed choroidal mast cells were of the connective tissue type. However, granule proteinase content appeared less than that of well characterised connective tissue mast cell populations such as those in mesentery and skin. Lewis rats exhibited the highest density of choroidal mast cells (23.6 (SD 1.2)/mm2), Wistar Furth approximately half that of Lewis (13.5 (0.7)/mm2) while PVG/c and brown Norway rats had very low densities (3.06(0.3); 1.95(0.2/mm2 respectively). These studies provide valuable choroidal mast cell data for rats which may have implications for our understanding of experimental models of intraocular inflammation and clinical uveitis.

Localization and characterization of major histocompatibility complex class II-positive cells in the posterior segment of the eye: implications for induction of autoimmune uveoretinitis

PURPOSE

To identify potential antigen-presenting cells in the choroid and retina of the normal rat eye, with a view to proposing a role for such cells in the induction and perpetuation of experimental autoimmune uveoretinitis, a model of human uveoretinal inflammation.

METHODS

Immunohistochemical and electron microscopic studies using a panel of monoclonal antibodies were performed on frozen sections of the perfused-fixed normal Lewis rat eye, choroid whole mounts, and cytospin preparations of cells harvested from choroid/ciliary body explant cultures. In addition, time-lapse video recordings of migratory uveal tract cells in culture were taken.

RESULTS

No major histocompatibility complex class II-positive cells were found in the normal Lewis rat retina. However, at least three populations of potential antigen-presenting cells were found in the uveal tissues of the eye: classical dendritic cells expressing high levels of major histocompatibility complex class II antigen; resident dendritiform macrophages, which were negative for major histocompatibility complex class II antigen, but expressed specific macrophage markers (ED2); and blood-borne macrophages (ED1) that had emigrated from the vasculature into the tissue compartment. In addition there were small numbers of cells expressing novel markers such as markers usually found only on macrophage subsets in splenic tissue (ED3) and a recently described marker for veiled dendritic cells (OX62). Dendritic cells and resident dendritiform macrophages closely interacted with each other and with tissue cells, particularly retinal pigment epithelial cells.

CONCLUSIONS

The posterior uveal tract is richly populated with classical dendritic cells expressing constitutive high levels of major histocompatibility complex class II antigen. There are also several types of macrophages with the potential to modulate immune responses in the posterior segment. Interactions among these cells and with resident tissue cells such as retinal pigment epithelial cells are probably central to the initiation of (auto)immune responses in the posterior segment of the eye.

Development of the eye in the North American opossum (Didelphis virginiana)

Marsupials are unique models for developmental biology-oriented research because of the immature state of their development at birth. The North American opossum (Didelphis virginiana) has several advantages over other marsupials, including large litter size, short prenatal period (12.5 d), an extended postnatal period while accessible in the pouch, and its ability to reproduce reliably in captivity. Studies of ocular development in this species have not been reported previously. The aim of the present investigation was therefore to document the major landmarks in prenatal and postnatal development of the cornea, lens, iris, ciliary body and retina. Fifteen embryos (10.5, 10.7 and 11 d postconception and 6 h after birth [12 d]) were studied by paraffin histology. Eyes of pouch young at 8 d, 2, 6, 9 and 13 wk were studied by transmission electron microscopy and light microscopy. The study revealed a similar pattern of ocular development in Didelphis to other metatherian and eutherian mammals. Differentiation of the eye is particularly rapid in the 2 d before birth. For example, although the lens vesicle separates from the surface ectoderm on d 10, by birth (2.5 d later) a primitive cornea and fused eyelids have formed, presumably to protect the eye during migration to the pouch. At birth the retinal pigment epithelium (RPE) contains melanin; however, the inner layer of the optic cup does not differentiate into an inner and outer neuroblastic layer until 8 d after birth. Around 6 wk after birth most components of the adult eye are identifiable, albeit in an immature form. These include the corneal layers, the iris (including the sphincter pupillae), ciliary processes, RPE tapetum, and a fully laminated retina with immature photoreceptors. A knowledge of the timing of major events in eye development in Didelphis and their comparison with equivalent events in human eye development should allow the appropriate choice of stages for any future experimental studies utilising this marsupial species.

Morphological observations on the unique paired capillaries of the opossum retina

Light-microscopic and ultrastructural analysis of the ocular tissues of the North American opossum (Didelphis virginiana) revealed that the arterial and venous segments of retinal vessels, including capillaries of the smallest calibre, occur in pairs. They do not form anastomotic networks, the common pattern in mammals with vascularised retinae, but instead the two segments of the pair join to form hairpin end loops. The paired vessels, with the arteriolar limb usually on the vitread aspect, penetrate the retina and branch to form three distinct layers of capillaries. The most superficial lies in the nerve fiber layer, the middle is situated in the inner nuclear layer and the deepest extends to the external limiting membrane, which is considerably deeper than in normal mammalian holangiotic retinae. The paired capillaries display classical morphological features of central nervous system capillaries, i.e., they are lined by continuous endothelial cells united by tight junctions. The lining endothelium is supported by a distinct basal lamina that splits to envelop pericytes. The latter, although abundant, are invariably interposed between the two vessels that form each vascular unit. Phylogenetic and functional aspects of this unique form of retinal vascularisation are discussed.

Downregulation of the antigen presenting cell function(s) of pulmonary dendritic cells in vivo by resident alveolar macrophages

Class II major histocompatibility complex (Ia)-bearing dendritic cells (DC) from airway epithelium and lung parenchyma express low-moderate antigen presenting cell (APC) activity when freshly isolated. However, this function is markedly upregulated during overnight culture in a manner analogous to epidermal Langerhans cells. The in vitro "maturation" process is inhibited by coculture with pulmonary alveolar macrophages (PAM) across a semipermeable membrane, and the degree of inhibition achieved can be markedly increased by the presence of tumor necrosis factor alpha. In addition, PAM-mediated suppression of DC function is abrogated via inhibition of the nitric oxide synthetase pathway. Functional maturation of the DC is accompanied by increased expression of surface Ia, which is also inhibited in the presence of PAM. Prior elimination of PAM from DC donors via intratracheal administration of the cytotoxic drug dichloromethylene diphosphonate in liposomes, 24-72 h before lung DC preparation, achieves a comparable upregulation of APC activity, suggesting that (consistent with the in vitro data) the resident PAM population actively suppresses the APC function of lung DC in situ. In support of the feasibility of such a regulatory mechanism, electron microscopic examination of normal lung fixed by intravascular perfusion in the inflated state (which optimally preserves PAM in situ), revealed that the majority are preferentially localized in recesses at the alveolar septal junctions. In this position, the PAM are in intimate association with the alveolar epithelial surface, and are effectively separated by as little as 0.2 microns from underlying interstitial spaces which contain the peripheral lung DC population. A similar juxtaposition of airway intraepithelial DC is demonstrated with underlying submucosal tissue macrophages, where the separation between the two cell populations is effectively the width of the basal lamina.

Ultrastructural pathology of experimental autoimmune uveitis in the rat

Experimental autoimmune uveoretinitis (EAU) has been extensively studied as a model for human posterior uveitis, however, few ultrastructural studies of EAU in the rat have been reported. In the present report we document a systematic time-course study of the posterior segment changes in the Lewis rat. The disease varied somewhat in severity in animals sacrificed at identical times after immunisation. In the prodromal stage of the disease, usually around day 14, early pathological changes included mild peripapillary vasculitis and low grade mononuclear and neutrophilic infiltration of the subretinal space with phagocytosis of the rod outer segments. The features of the severe or active diseases were most evident on day 21 and included mixed cellular infiltrate of the vitreous, subretinal serohaemorrhagic exudate, focal retinal detachment and necrosis. Outer retinal destruction was often most severe adjacent areas of retinal vasculitis. Focal monocytic subpigment epithelial microgranulomas, reminiscent of Dalen-Fuch's nodules in humans, were also identified. By day 28 and 49 active inflammation had subsided and large segments of the outer retina were completely destroyed. The retinal pigment epithelium (RPE) also showed signs of activation in the vicinity of focal retinochoroidal mononuclear infiltrates including multilayering, proliferation and increased phagocytosis. Finally, neovascularisation of the RPE by non-fenestrated capillaries derived from the retinal vasculature was evident in the late stages of the disease.

Experimental autoimmune uveoretinitis: a model system for immunointervention: a review

Experimental autoimmune uveoretinitis (EAU) is a useful model of human posterior uveitis and as such, permits the analysis of strategies for immuno-intervention. Modulation of the autoimmune response may be attempted at the stages of induction of EAU, during homing of autoreactive lymphocytes to the target organ, the retina, or during the effector stage of the disease. This paper presents a brief overview of current immuno-therapeutic modalities and assesses the usefulness for extrapolation to human disease.

Class II major histocompatibility complex (Ia) antigen-bearing dendritic cells within the iris and ciliary body of the rat eye: distribution, phenotype and relation to retinal microglia

The density, distribution and surface phenotype of dendritic cells (DC) and macrophage populations within the ciliary body and iris of Wistar Furth rats were studied by a combination of flat mounting, tangential sectioning, pre-embedding fixation, with a single and double immunohistochemical techniques. Monoclonal antibodies included anti-Ia (OX6) and other dendritic cell/macrophage (ED1 and ED8) or mature tissue macrophage markers (ED2). Single and double staining revealed a network (approximately 400 cells/mm2) of Ia+ cells within the epithelium of the ciliary processes with the morphological and surface phenotypic characteristics of DC populations in other tissues. A minor proportion of DC co-expressed ED1 and ED8, but not ED2. In contrast the immunopositive cells in the lamina propria displayed a more generalized phenotype, including ED2 expression, and pleiomorphic morphology suggesting a preponderance of cells of macrophage lineage. Flat mounts of iris revealed a remarkably regular network of Ia+ DC at a density of 450 cells/mm2. The network of DC in the ciliary epithelium terminated at the cilioretinal junction where they formed a continuous syncytium with retinal microglia which did not display Ia staining. The demonstration of networks of cells with relevant morphological and phenotypical properties of professional antigen-presenting cells at strategic locations within the eye has important implications in relation to ocular immune regulation and on the theories of the mechanism of anterior chamber-associated immune deviation (ACAID). Namely, until now it has been assumed that 'immune privilege' in the anterior chamber of the eye is partly a consequence of there being a paucity of class II+ cells in the surrounding tissues. Dendritic cells in the eye may function as antigen-presenting cells, sampling endogenous and exogenous intraocular antigens and possibly migrating from the eye to draining lymphoid organs (the spleen) where they may generate systemic immune responses. Equally dendritic cells could potentially regulate local immune responses for example in various forms of autoimmune uveoretinal inflammatory disease.

Immunohistochemical characterization of dendritic cells and macrophages in the aqueous outflow pathways of the rat eye

Immunohistochemical studies were performed to determine the distribution, phenotype and ontogeny of macrophages and dendritic cells (DCs) in the aqueous humour outflow pathways of the rat eye. Optimal fixation and indirect immunoperoxidase techniques were employed in conjunction with a panel of mAbs on tangential frozen sections of ocular tissues from a total of 37 Wistar Furth rats aged 12-13 days (n = 8), 3 weeks (n = 12), 7 weeks (n = 5) and 15 weeks (n = 12). The density of immunopositive cells was scored qualitatively. A moderate to low density of Ia+ cells with a dendritic morphology were observed in the trabecular meshwork. DCs were also identified in the suprachoroidal space and in the connective tissues of nerves and vessels piercing the sclera, i.e. in association with non-conventional aqueous outflow pathways. The phenotypical and morphological characteristics of these cells would indicate that they may potentially act as antigen presenting cells (APCs). Non-dendritic pleomorphic cells with a macrophage phenotype were also identified in the trabecular meshwork, and bipolar or elongated cells with a macrophage phenotype were a noticeable feature in the perivascular region of collector channels and the limbal episcleral veins. Some macrophage and DC-like cells were observed in intimate association with limbal mast cells. Theories on the mechanisms of Anterior Chamber Associated Immune Deviation (ACAID) have assumed APCs are largely absent from the tissues lining the anterior chamber. Our findings of a low but moderate density of putative APCs in the conventional and non-conventional aqueous humour outflow pathways are discussed in relation to the various theories of ACAID.

Ultrastructural pathology of experimental autoimmune uveitis. Quantitative evidence of activation and possible high endothelial venule-like changes in retinal vascular endothelium

BACKGROUND

Experimental autoimmune uveitis (EAU) is a highly organ-specific autoimmune disease in which the target is the retinal photoreceptors. It is well recognized as a model of uveoretinitis in humans. The mechanisms that control the homing of sensitized lymphocytes and other leukocytes to the retina is unknown. The aim of this study was to investigate changes in the retinal vasculature that may be involved with aiding leukocyte-endothelial cell interactions and subsequent extravasation of leukocytes into the retina.

EXPERIMENTAL DESIGN

Lewis rats immunized with S-antigen were used to produce EAU. The retinal vasculature was assessed by morphologic (light and electron microscopy) and morphometric techniques at various stages in the generation and course of the disease (days 3, 7, 11, 14, 21, 28 and 49 postimmunization) for evidence of endothelial cell (EC) activation and leukocyte-EC interaction. Image analysis of the retinal vessels at the electron microscopic level was performed to detect alterations in the thickness and irregularity of the EC surface, both considered to be important in lymphocyte homing in the high endothelial venules (HEVs) of lymphoid tissues. Control values were obtained from normal eyes, pertussis-only treated animals, and normal lymph node HEVs.

RESULTS

The clinical and histopathologic changes in the eyes were consistent with previous descriptions of EAU and included perivasculitis, focal mononuclear infiltrate in the outer retina, and choroid with destruction of the photoreceptor outer segments and eventually loss of large portions of the outer retina. During the course of EAU, a significant proportion of retinal venules underwent both qualitative and quantitative morphologic changes including EC activation evident as increased cytoplasmic organelles, a 230% average increase in mean EC thickness, and a concomitant 4-fold increase in irregularity of the EC, that produced plump irregular EC with deep intercellular clefts. These alterations were maximal at day 21, however from day 11 onward, large numbers of lymphocytes and monocytes were observed adhering to or lodged in the clefts of plump EC, migrating through the EC cytoplasm, or lying beneath the EC.

CONCLUSIONS

The characteristics acquired by the retinal venules during EAU are reminiscent of HEVs. This study suggests that tissue-specific changes in the endothelial cells of retinal venules may be responsible for the homing of S-antigen specific autoreactive lymphocytes to the target organ in this model of retinal autoimmunity.

Morphological observations on the harderian gland of the North American opossum (Didelphis virginiana)

The Harderian gland of the North American opossum (Didelphis virginiana) is large and well developed, despite the absence of a nictitating membrane in the adult of this species. The elongate glands are surrounded by a delicate connective tissue capsule from which thin septae extend, subdividing the gland into numerous lobules. The secretory units of the opossum Harderian gland are drained by a well defined but not extensive intralobular and interlobular duct system. Most of the secretory end pieces consist of tubulo-alveolar units with widely dilated lumina filled with secretory product. Numerous intact lipid vesicles suspended within an amorphous material constitute the luminal contents. Cells lining the tubulo-alveolar secretory end-pieces are usually columnar in shape, and characterized by numerous lipid-containing secretory vesicles and aggregations of poly-tubular complexes 40-60 nm in diameter. In addition, these cells contain numerous large irregularly shaped mitochondria, whose matrix is of considerable electron density. Intralobular and interlobular ducts are lined by electron-lucent epithelial cells that lack both the lipid-containing vesicles and the large mitochondria, although typical smaller mitochondria are found scattered within the cytoplasm. Both secretory end-pieces and ductal elements are invested by an abundance of myoepithelial cells. A second, smaller serous type of secretory unit may occur near the centre of some Harderian gland lobules. In these units secretory tubules and acini are compactly arranged surrounding a narrow lumen. Serous cells are pyramidal in shape and the cytoplasm is characterized by numerous electron-dense secretory granules and scattered profiles of rough endoplasmic reticulum.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative study of the prenatal development of the aqueous outflow system in the human eye

There is a multiplicity of theories on the development and differentiation of the human iridocorneal angle. Many have arisen from the need to explain the pathogenesis of primary infantile (congenital) glaucoma or other related developmental disturbances. The present study, which is the first light and electron microscopical morphometric analysis of human fetal eyes, was designed to determine the nature of the changes in various tissue components during trabecular anlage formation and differentiation (between 12 and 22 weeks of gestation). The results demonstrate that the trabecular anlage doubles in cross-sectional area during this period. However, when circumferential growth is considered there is in fact a threefold increase in anlage volume. Cell density in sections decreases over the 10-week period, as does the number of cells per unit volume. However, employment of stereological analysis together with corrections for volume changes revealed a two to threefold increase in absolute number of cells per eye (2.8 x 10(5) to 7.5 x 10(5)). Relative and absolute volume data on the four major constituents of the trabecular anlage show that extracellular matrix increases in the most significant and predictable fashion (360% in absolute volume), with the increase in intertrabecular spaces being more variable (200%). The findings are discussed in relation to previous theories of trabecular meshwork development.

Normal anatomy of the aqueous humour outflow system in the domestic pig eye

The normal functional anatomy of the aqueous humour outflow pathways in the domestic pig is poorly documented in the literature despite its being readily available and of a similar size to the human eye. Anterior segment tissue from 12 pig eyes was appropriately fixed and investigated by light microscopy, and scanning and transmission electron microscopy. The configuration of the iridocorneal angle tissues is similar to other nonprimate mammals in several respects, i.e. it possesses a deep ciliary cleft crossed by stout pectinate ligaments and delicate uveal cords, poorly developed ciliary musculature, and an angular aqueous plexus. However, there were some noteworthy features which may make it a suitable model for specific types of glaucoma related research. These features include a shallow scleral sulcus which contains a wedge-shaped mass of corneoscleral tissue comparable in size to the human trabecular meshwork. This tissue was more trabecular than 'reticular' in arrangement, the latter being the more common in nonprimate mammalian species. The relevance of the present findings to the use and limitations of the porcine eye as a model of the human aqueous outflow pathways is discussed.

Laryngeal cancer: diagnosis, treatment and speech rehabilitation

Cancer of the larynx occurs most often in men between 50 and 70 years of age. Cigarette smoking and alcohol are responsible for more than 75 percent of cases. Hoarseness is the most common presenting complaint. If hoarseness persists for more than two weeks, laryngoscopy is indicated. Clinical staging utilizes direct laryngoscopy, esophagoscopy and bronchoscopy to exclude synchronous malignancies. The five-year cure rate, with preservation of voice and glottic function, is as high as 90 percent if the lesions of the vocal cords are found in an early stage. Total laryngectomy is required for more extensive disease. Speech rehabilitation has been revolutionized by tracheoesophageal speech techniques.

Ultrastructural pathology of the 'barrier sites' in experimental autoimmune uveitis and experimental autoimmune pinealitis

Lewis rats were immunised with retinal S-antigen to induce experimental autoimmune uveitis and experimental autoimmune pinealitis. The blood-retinal and blood-pineal 'barrier sites' were examined by transmission electron microscopy. Inflammatory cell movement through Bruch's membrane involved separation of its constituent layers, cell migration through pores in the membrane, and between retinal pigment epithelial cells without causing significant displacement of the retinal pigment epithelial cell layer. The endothelial cells of retinal and pineal vessels with perivascular infiltrates showed morphological features resembling endothelium of 'high endothelial venules'.

Studies on the density, distribution, and surface phenotype of intraepithelial class II major histocompatibility complex antigen (Ia)-bearing dendritic cells (DC) in the conducting airways

Conventional immunohistochemical analysis of airway intraepithelial class II major histocompatibility complex (Ia) expression demonstrates a morphologically heterogeneous pattern of staining, suggestive of the presence of a mixed population of endogenous antigen presenting cells. Employing a novel tissue sectioning technique in conjunction with optimal surface antigen fixation, we now demonstrate that virtually all intraepithelial Ia staining throughout the respiratory tree in the normal rat, can be accounted for by a network of cells with classical dendritic cell (DC) morphology. The density of DC varies from 600-800 per mm2 epithelial surface in the large airways, to 75 per mm2 in the epithelium of the small airways of the peripheral lung. All the airway DC costain for CD4, with low-moderate expression of a variety of other leukocyte surface markers. Both chronic (eosinophilic) inflammation and acute (neutrophilic) inflammation, caused respectively by inhalation of chemical irritants in dust or aerosolised bacterial lipopolysaccharide (LPS), are shown to be accompanied by increased intraepithelial DC density in the large airways (in the order of 50%) and up to threefold increased expression of activation markers, including the beta chain of CD11/18. The kinetics of the changes in the DC network in response to LPS mirrored those of the transient neutrophil influx, suggesting that airway intraepithelial DC constitute a dynamic population which is rapidly upregulated in response to local inflammation. These findings have important theoretical implications for research on T cell activation in the context of allergic and infectious diseases in the respiratory tract.

Evaluation of subretinal macrophage-like cells in the human fetal eye

In many ocular diseases, macrophages are found in the subretinal space and probably play an important role in maintaining the disease process. Several issues concerning these cells are still unclear, such as their route of entry or their relation to the retinal pigment epithelium. The authors have found that the human fetal eye contains macrophage-like cells in the peripheral subretinal space. Their localization, distribution, and ultrastructural features are evaluated in 33 eyes from 17 specimens (12 to 22 weeks gestational age) by light microscopy and scanning and transmission electron microscopy. Subretinal macrophage-like cells occurred predominantly in the region of the ciliary folds. They were observed within the peripheral neural retina, beneath the retinal and ciliary pigmented epithelia, under Bruch's membrane, and in the choroid. This distribution suggests that one of the main entry pathways is through the vascular bed of the ciliary body. There were approximately nine subretinal space macrophages per 0.1 mm2 distributed in a regular fashion on the retinal pigment epithelial surface close to the ciliary folds, however, the incidence decreased further posteriorly where they were very rare. Their shapes varied from large flat cells with several long processes to more spherical cell bodies with a few membrane ruffles. There was also evidence that some of these cells had recently phagocytosed cell debris, including retinal pigment epithelial premelanosomes. Morphologically, these cells closely resemble supraependymal and epiplexus cells, the macrophage populations found on the cerebral ventricles, an environment that corresponds anatomically to the subretinal space.(ABSTRACT TRUNCATED AT 250 WORDS)

Cells resembling intraventricular macrophages are present in the subretinal space of human foetal eyes

The subretinal spaces (SRS) in 17 human foetal eyes were investigated by light microscopy and scanning and transmission electron microscopy. A hitherto undocumented group of pleomorphic cells was detected on the apical surface of the retinal pigment epithelium (RPE) and on the undersurface of the neural retina. These cells formed a regularly spaced array in the peripheral SRS, particularly in the most anterior portion nearest the ciliary body anlage. The morphology of the SRS cells ranged from a small round or ovoid form with a few short basal pseudopodia to an extremely flattened dendritic form. Ultrastructural features, such as large melanophagolysosomes, consistent with a phagocytic function, were observed in some cells. These SRS cells bore remarkable resemblance to epiplexus and supraependymal cells, considered to be the resident population of macrophages on the ventricular surfaces of the brain. This morphological parallelism, together with the anatomically homologous location, is strong evidence that SRS cells represent a normal population of macrophages in the developing human eye. No features consistent with an RPE or neuronal origin were observed. The possible role of these cells as transient phagocytes in the SRS with a possible destiny as retinal microglia is discussed.

Dendritic cells in the respiratory tract

Studies from several laboratories on lung tissue samples from human and experimental animals have identified Ia+ cells with characteristic pleiomorphic (dendritic) morphology in the epithelium and underlying connective tissue, in both the conducting airways and in the distal lung. These dendritic cells (DC) are particularly prominent within the airway epithelium, forming a contiguous network equivalent to the Langerhans cells network of the epidermis. They may be readily concentrated from enzymatically disrupted respiratory tract tissue samples on the basis of their physical properties (notably non-adherence, lack of Fc-receptors and ultra-low density on percoll), and function as highly effective antigen presenting cells in vitro. Evidence is also accumulating that respiratory tract DC populations respond dynamically to local tissue inflammation, and as such may play a prominent role in immunoinflammatory disease processes in the airways and the distal lung.

A contiguous network of dendritic antigen-presenting cells within the respiratory epithelium

This study utilises a simple technique to section airway epithelium in a plane parallel to the basement membrane, thus providing a unique plan view of the intra-epithelial cell populations. Immunoperoxidase staining of these tissue sections for class II major histocompatibility complex Ia antigen reveals a virtually contiguous network of Ia-positive dendritic cells (DC) within the epithelium. These DC are shown to be capable of binding inhaled antigens in vivo in a form suitable for presentation to T cells. The strategic location of these cells and the fact that they account for virtually all staining in the airway epithelium during the steady state is convincing evidence that the DC network functions as the 'first line of defence' in surveillance for inhaled antigens and further suggests a major role for the intra-epithelial DC in allergic and infectious disease(s) in the respiratory tract.

Comparison of clinical and experimental uveitis

Uveitis is a term which encompasses many clinical syndromes which would appear to be discrete entities. Both clinically and experimentally, the separation of uveitis affecting only the anterior segment from that affecting the posterior segment has a sound pathogenetic basis. However, clear distinctions among the various forms of endogenous posterior uveitis are more difficult to maintain in the light of evidence from experimental models of autoimmune uveitis (EAU). EAU can be induced by a variety of retinal antigens and each antigen has been shown to induce somewhat different forms of EAU, depending on such factors as dose of antigen, species and strains of animal model, and the type(s) of adjuvant used. However, within each model a similar spectrum of uveoretinal responses can be induced by each antigen suggesting that the pathogenetic mechanisms are probably similar also. In addition, if these models are analogous to human disease, then each clinical entity within this apparently heterogeneous group of clinical posterior uveitis syndromes may represent one aspect of a general organ-specific uveoretinal response to autoantigens.

Human fetal iridocorneal angle: a light and scanning electron microscopic study

The iridocorneal angle and inner layers of the trabecular meshwork in human fetal eyes were studied by scanning electron microscopy. Tissue from 32 eyes of 17 fetuses with a gestational age from 12 to 22 weeks were investigated in order to determine the morphological changes in the cellular lining of the anterior chamber angle recess during development. The findings indicate that, although hexagonal corneal endothelial profiles extend almost to the angle apex in a few of the younger eyes examined (12-14 weeks), the lining is always perforated by a few discrete intercellular gaps (2-6 microns diameter). As development progresses it becomes clearer that the maturing meshwork is lined by uveal trabecular endothelial cells which are morphologically distinguishable from corneal endothelium. The frequency and size of the gaps between the inner uveal trabecular endothelial cells increase and are well developed by 18-20 weeks, clearly providing a route of communication between the fetal anterior chamber and the developing intercellular spaces in the primitive trabecular tissue. The implications of these observations on the 'Barkan's membrane' theory of congenital glaucoma are discussed.

Ia-positive dendritic cells form a tightly meshed network within the human airway epithelium

In this report we have employed an alternative tissue-sectioning procedure which provides a plan view of intra-epithelial cell populations within the airway wall. Immunoperoxidase staining of such sections for class II MHC (Ia) antigen revealed the presence of a highly developed intra-epithelial network of Ia-positive dendritic cells, which was not evident employing conventional cross- or longitudinal tissue sections. This finding has important implications for the study of mechanisms underlying allergic and infectious diseases of the respiratory tract.

A morphological study of the inner surface of the anterior chamber angle in pre and postnatal human eyes

The morphological changes in the inner surface of the human anterior chamber angle during pre and postnatal development were studied by light microscopy, scanning and transmission electron microscopy. Seventeen human foetal eyes (12-22 weeks) and ten infant and juvenile eyes (2.5 months--8 years) were investigated with the aim of establishing whether the trabecular meshwork is covered by an uninterrupted membrane at any stage in development. In 12-14 week old foetal eyes cuboidal corneal endothelial cells cover the inner surface of the anterior half to one third of the trabecular anlage. In this region there is a transition to more flattened uveal trabecular endothelial cells. Only rarely did corneal endothelial cells extend completely to the angle apex. The transition zone between corneal and uveal trabecular endothelial cells becomes located more anteriorly as development progresses. Intercellular gaps, which occur between uveal trabecular endothelial cells as early as 12-14 weeks in development, enlarge and become more frequent during development thus providing a route of communication between the anterior chamber and the developing intertrabecular spaces or channels. In the first months of life only a few cord-like uveal trabeculae orientated predominantly in a meridional direction overlie the more lamellate corneoscleral trabeculae. By the second year typical uveal trabeculae are more prominent and form a web-like arrangement. This is accompanied by a gradual decrease in the frequency of the cytoplasmic extensions of uveal trabecular endothelial cells which circumscribe the intratrabecular gaps. The timing of this remodelling and maturation appears to be remarkably variable between individuals. The implications of these findings on the theories of the pathogenesis of congenital glaucoma are discussed.

Prostatic carcinoma presenting with neck metastasis

Prostatic carcinoma is the second leading cause of cancer mortality in American men. Twenty-seven thousand deaths from this aggressive neoplasm were predicted for 1987. Although this malignancy has metastasized to almost all of the structures in the head and neck, it demonstrates a pathophysiologic proclivity for the supraclavicular lymph nodes. Combining fine-needle aspiration with immunohistochemical techniques produces a cost-effective method to expedite the diagnosis of this hormone-responsive tumor. Four patients presenting with prostatic carcinoma and neck metastasis in a three-year period are reported and discussed.

The effect of various levels of intraocular pressure on the rat aqueous outflow system

The eyes of 20 normal mature Swiss albino rats were fixed by intracameral perfusion with glutaraldehyde at various levels of intraocular pressure (10, 20, 30 and 40 mmHg). The anterior chamber was connected by a fine cannula to a reservoir of fixative for 10 minutes while the animal was maintained under anaesthesia for a further 20 minutes after death. Five animals were studied at each pressure. Fixation at 0 mmHg was achieved by rapid immersion of enucleated eyes from 5 animals whose eyes had been cannulated and open to atmospheric pressure for the first 10 minutes. The anterior segment tissues were studied by light microscopy and by scanning and transmission electron microscopy. The eyes from rats fixed by cardiac perfusion provided control tissue. Progressive increase in intraocular pressure produced varying degrees of structural alterations in the iridocorneal angle. These included widening of the ciliary cleft and enlargement of the spaces of Fontana; however, the pectinate ligaments remained intact even at the highest pressure. The trabecular tissues became more distended and there was a statistically significant relationship between the fixation pressure and the mean number of giant vacuoles in the inner wall of Schlemm's canal. The response between animals fixed at the same pressure was variable. This was most pronounced at 10 and 40 mmHg. The results indicate that the rat outflow system responds morphologically to various levels of experimentally induced intraocular pressure in a similar fashion to primates. These findings, together with the morphological similarities between the rat and primate aqueous humour outflow pathways, particularly the presence of a single canal of Schlemm, suggest that the rat may be a valuable model for future studies of the normal and abnormal mechanisms of aqueous drainage. The technical difficulties of experimental studies of the aqueous drainage mechanism in such a small eye are discussed.