Perioperative socialization, care and monitoring of National Institutes of Health miniature swine undergoing ocular surgery and sampling of peripheral blood

Swine are a frequent species of choice for testing new surgical procedures and for transplantation studies. However, information concerning best practice to prepare pigs for surgery and postoperative treatment and monitoring is limited, despite a perception that preoperative socialization is beneficial. Therefore we examined the effect of preoperative visits by project personnel on compliance of 26 National Institutes of Health (NIH) minipigs subject to corneal transplantation. We briefly describe sedation and anaesthesia protocols developed for surgery and multiple postoperative interventions in order to facilitate interpretation of data relating to pig compliance. Preoperative visit variables and measures of preoperative socialization were correlated with postoperative outcome. Principal component analysis (PCA) of postoperative outcome variables identified a factor accounting for 53.5% of the variance that was significantly associated with two factors derived from PCA of preoperative factors (accounting, respectively, for 54.7% and 26.0% of the variance; P = 0.019 for the overall model, P = 0.041 and 0.040 for factors 1 and 2, respectively), such that more time spent with pigs before surgery and higher socialization scores were associated with less postoperative stress and difficulty of eye medication. Moreover, two of the preoperative visit variables, time spent with only one person in the pen and time spent with two or more people in the pen, contributed predominantly to PCA factors 1 and 2, respectively, indicating that they were fulfilling two qualitatively different requirements for socialization. We conclude that NIH minipigs are fully compliant with anaesthetic and postoperative experimental procedures provided they are well-socialized to project personnel before surgery.

Development of organised conjunctival leucocyte aggregates after corneal transplantation in rats

AIM

To investigate the development of lymphoid aggregates in the conjunctiva after corneal transplantation in rats.

METHODS

LEW or PVG strain corneas were transplanted orthotopically to PVG rats. Cornea and conjunctiva were examined clinically for up to 42 days. Eyes were removed with attached conjunctiva on days 10 and 15 after transplantation (before and during rejection), together with normal eyes, fixed, paraffin embedded, and examined immunohistochemically.

RESULTS

Clinically, the temporal half of the upper palpebral conjunctiva of recipients of 10/19 allografts and 1/10 isografts developed pronounced swelling, correlating with inflammation and rejection. Histologically, the swelling comprised leucocytic aggregates with an altered overlying epithelium. Aggregates contained granulocytes, macrophages, and cells expressing major histocompatibility complex (MHC) class II, CD4, and CD8, all more numerous in allograft associated conjunctiva. Class II+ cells were more abundant at the surface, whereas macrophages and T cells were more numerous in the deeper stroma. There were few B cells. There was greater CD54 expression by vascular endothelium in allograft associated aggregates. Cells expressing TNFalpha and IFNgamma but not IL1beta were present in stromal and superficial areas.

CONCLUSIONS

Corneal transplantation in rats induces the development of organised conjunctival leucocytic aggregates in a fixed location that are significantly more pronounced in recipients of allografts compared with isografts and show characteristics of a Th1 type immune response. These aggregates have characteristics of conjunctiva associated lymphoid tissue and may be sites of presentation of graft antigens and lymphocyte proliferation at the ocular surface.

MHC matching and mechanisms of alloactivation in corneal transplantation

BACKGROUND

In human corneal transplantation the value of matching, particularly for MHC class II, is unclear and controversial. The contribution of the direct pathway to T cell activation is also uncertain. We have determined the relative contribution of class I, II and non-MHC antigens to graft rejection and of the direct and indirect pathways to T cell activation in a rat model mimicking human incompatibilities.

METHODS

DA (RT1a) strain recipients received fully mismatched PVG (RT1c) strain grafts or grafts from one of three recombinant strains bearing DA MHC genes on a PVG background. Graft survival was assessed and the specificity of T cells generated in the draining lymph nodes was determined in mixed lymphocyte (MLR) proliferation assays. To assess the contribution of the direct pathway, fully mismatched graft were performed and allospecific proliferation was measured after depletion of recipient APC from the MLR reaction.

RESULTS

There was no significant difference in survival of grafts between the four grades of mismatch, which ranged from a full mismatch to non-MHC mismatches alone (median survival 12.5, 11, 13 and 12.5 days respectively). In conformity with clinical results, strong secondary responses were generated against targets matched for MHC with the recipient. Depletion of recipient APC from a fully allogeneic secondary MLR did not fully abrogate donor-specific proliferation.

CONCLUSIONS

Class II matching is of no benefit in this model. Strong indirect responses to non-MHC mismatches are sufficient to induce the rapid rejection, but the small numbers of class II+ cells in the donor appear sufficient to generate a direct response.

An improved method for examining the corneal endothelium during graft rejection in the rat

An improved method of removing rat corneal endothelial sheets for study of endothelial pathology is described. The method was validated by examining morphological changes and changes in expression of major histocompatibility complex (MHC) and intercellular adhesion molecule (ICAM)-1 on endothelium undergoing immunological rejection. PVG strain rats received LEW strain corneal transplants or corneal isografts. Just prior to and during graft rejection, animals were killed, together with a group of untreated animals. The corneal stroma was injected with dispase or PBS, the cornea was carefully removed, fixed in acetone and the endothelium was gently peeled off and flattened on to a glass slide. Morphological changes, together with MHC class I, class II and ICAM-1 expression were visualised by immuno-histochemical staining and quantified by image analysis. Near complete endothelial sheets were obtained by this method. Because of the thin cell layer, there was minimal background staining, permitting rejection-associated changes to be clearly seen. MHC class I expression on normal endothelium was low and not significantly increased on endothelial cells of allografts at the time of rejection compared with controls (P = 0.1). MHC class II and ICAM-1 were induced de novo, expression being significantly higher on allografts than on isografts (P = 0.004 for MHC class II and P = 0.01 for ICAM-1). MHC class I and II and ICAM-1 were expressed on many infiltrating cells. Thus, this preparation method permits clear identification of the distribution and morphology of infiltrating cells and other mediators of the immune response in the entire donor endothelium. It confirms that MHC class I expression is low during rejection, while MHC class II and ICAM-I are induced de novo and strongly expressed.

A murine model of interlamellar corneal transplantation

AIMS/BACKGROUND

There are more reagents and information available for immunological studies in the mouse compared with other animals. Unfortunately, the mouse penetrating keratoplasty model is associated with high background inflammation which hinders study of the immune response to the graft. To mitigate this drawback, a murine orthotopic corneal interlamellar transplantation model with mild non-specific inflammation was developed.

METHODS

A 1.5 mm diameter full thickness donor corneal button was placed in a 2 mm diameter recipient corneal interlamellar pocket without placement of a suture. The clinical course of graft status was studied daily for 60 days in 30 allografts (donor strain CBA 101 (H-2k) to recipient NIH (H-2q) and 30 syngeneic grafts (NIH to NIH) by slit lamp biomicroscopy and scored for neovascularisation, opacity, oedema, and granularity. In another cohort of animals, histological observation was performed after 30 minutes and on days 10, 20, 30, and 40 after transplantation (four allografts and four syngeneic grafts per time point). Histological study was also performed on grafts without donor epithelium and on interlamellar pockets without grafts.

RESULTS

There was significantly more neovascularisation (NV), opacity, oedema, and granularity in 24/30 allografts (80%) than in syngeneic grafts. Such grafts were defined as rejected. The median time to rejection was 21 days (range 18 to > 60 days). By histology, some allografts showed moderate to heavy cell infiltration which correlated with clinical scores of NV (4-5), opacity (1-3), oedema (1-3), and granularity (1-3). Such infiltration was absent in other allografts and syngeneic grafts.

CONCLUSION

Surgically, corneal interlamellar transplantation could be accomplished in the mouse and rejection could be clearly defined. The model can therefore be useful for in situ study of cell and molecular aspects of corneal graft rejection.

Immunohistochemical detection of cytokines in paraffin-embedded mouse tissues

We have successfully developed a method for the immunohistochemical detection of interleukin 2 (IL-2), IL-4, IL-6, IL-10O, IFNgamma and TNFalpha using monoclonal antibodies (MAb), in sections of mouse tissue embedded in paraffin wax. The method involved fixation in periodate-lysine-paraformaldehyde (PLP), rapid dehydration and infiltration under vacuum with paraffin wax at 54 degrees C. Comparative observations demonstrated that the method gives equivalent or better results than formaldehyde fixed, frozen sections. Since reliable controls, both positive and negative, are paramount for interpretation of immunohistochemical staining, such controls were determined. The following tissues were shown to be suitable as positive controls when using paraffin-embedding: spleen for the detection of TNFalpha, small intestine for IL-2, IL-4 and IL-10, and HSV-1 infected eyes for IL-6 and IFNgamma. We conclude that PLP fixation and low temperature paraffin-embedding is a method which provides both preservation of excellent tissue morphology and reliable immunohistochemical identification of cytokines. These attributes will be invaluable in a wide variety of experimental situations.

Immune cell infiltration in corneas of mice with recurrent herpes simplex virus disease

Reactivation of latent herpes simplex virus type 1 (HSV-1) infection was induced by UV irradiation of the corneas of latently infected mice. On days 1-4 after stimulation, infectious virus was sought in nervous and ocular tissue. On days 4, 7 and 10, eyes with either recurrent epithelial or stromal disease and appropriate controls were stained to identify immune cells and HSV-1 antigens. The maximum incidence of infectious virus was on day 2 when 5/10 ophthalmic parts of the trigeminal ganglion yielded HSV. Thus in this mouse model, as in humans, reactivation of virus in the trigeminal ganglion is the likely source of virus producing recurrent disease and shedding in the tear film. On day 4, when virus antigens were still present, granulocytes were the predominant infiltrating cell in corneas with either type of disease. Small numbers of T cells, dendritic cells and cells expressing MHC class II were also present. In stromal disease, the granulocyte infiltrate persisted and T cells remained sparse. In contrast, in epithelial disease, granulocyte numbers rapidly declined and both CD4+ and CD8+ T cells (present at a ratio of 1:1) increased significantly. The secondary immune response to virus antigen is more rapid and vigorous than that during primary corneal infection. Granulocytes may play a role in the initial clearance of virus, however, the other types of cells present early on provide the potential for a local secondary immune response. The high proportion of CD8+ cells in epithelial disease compared with stromal disease suggests that they may be acting as suppressors.

Recurrent herpes simplex after corneal transplantation in rats

PURPOSE

To ascertain the effect of trauma from surgery and rejection on the incidence and timing of recurrent herpes simplex virus (HSV) disease after corneal transplantation. To locate virus antigen and identify cells of the immune system infiltrating corneas with recurrent disease.

METHODS

PVG rats were inoculated on the cornea with HSV-1 McKrae. Recurrent disease was induced either by ultraviolet (UV)-irradiation of the cornea or by corneal transplantation. After corneal transplantation, animals shedding virus in the tear film were killed on days 1 to 4 of shedding. Eyes were fixed, embedded, sectioned, and stained for virus antigens, infiltrating cells, major histocompatibility complex class II, and adhesion molecule molecule expression.

RESULTS

In the first 15 days after corneal transplantation, 8 of 91 rats shed virus, and between days 16 and 30, an additional 3 of 60 rats shed virus (12% of total rats, comparable to the percent that shed after UV irradiation). Shedding sometimes was accompanied by punctate epithelial lesions in the recipient cornea and stromal opacity. The rejection process itself did not induce or exacerbate recurrent disease. In all corneas examined from eyes that shed virus, antigen was found in several locations at the graft-host junction, sometimes in the absence of clinical signs of disease, and frequently it extended through the stroma to the endothelium. Granulocytes were the main infiltrating cell in areas of virus antigen.

CONCLUSIONS

Corneal transplantation trauma is a stimulus to recurrent disease of similar potency to UV irradiation. The graft-host junction is an area in which virus spreads easily and can reach the endothelium readily. In humans, the incidence of recurrent disease at this location may be greater than has been recognized.

Immune cell infiltration and persistence in the mouse trigeminal ganglion after infection of the cornea with herpes simplex virus type 1

Following inoculation of the mouse cornea with herpes simplex virus type 1 (HSV-1), the spread of virus was investigated and the types of immune cell infiltrating the trigeminal ganglion (TG) were identified in low temperature paraffin wax sections. Virus antigen was first found on day 3 and was absent after day 14. Early presentation of antigen to T cells may occur since increased expression of major histocompatibility complex (MHC) class II antigens, including de novo expression on satellite and Schwann cells, was detected in foci of such antigen on day 3. A second large peak of such expression was detected on day 10 together with increasing numbers of B and T cells. Large numbers of these lymphocytes and extensive expression of MHC class II were seen in the TG well into the phase of virus latency; the significance of this is discussed.

Non-MHC antigens and their relative resistance to immunosuppression after corneal transplantation

We have used a high responder rat model to examine the role that non-MHC antigens play in corneal graft rejection. Recipients were backcross animals derived from a cross between two inbred strains, which mimicked the human outbred population in that donor and recipient could be matched or mismatched for MHC antigens, while non-MHC mismatches were variable and unknown. All mismatched grafts and 87% of matched grafts were rejected (median survival 11 and 17 days respectively). The high incidence of rejection of matched grafts indicates that several independently segregating non-MHC genes play a role in rejection. Moreover, the immune response to matched grafts appeared resistant to immunosuppression, suggesting that matching does not permit reduced dosage of immunosuppressants. A mechanism is discussed whereby matching at the class II locus may enhance presentation of mismatched histocompatibility antigens or viral peptides derived from infected graft cells, thereby prejudicing graft survival.

Immunohistochemical detection of T-cell subsets and other leukocytes in paraffin-embedded rat and mouse tissues with monoclonal antibodies

We describe a method for immunohistochemical localization of T-cells, CD4+ T-cells, CD8+ T-cells, B-cells, activated lymphocytes, major histocompatibility complex (MHC) class II antigens, macrophages, dendritic cells, and granulocytes in rat and mouse tissue fixed in periodate-lysine-paraformaldehyde (PLP) and embedded in paraffin. Rat and mouse spleen and eyes were fixed in PLP for 18-24 hr, rapidly dehydrated, infiltrated under vacuum with paraffin at 54 degrees C, sectioned, and stained with appropriate monoclonal antibodies (MAbs). Sections of PLP-fixed, paraffin-embedded spleen were compared with acetone-fixed frozen spleen sections with respect to morphology and staining quality. Nine of 10 MAbs to rat antigens and eight of nine MAbs to mouse antigens stained paraffin sections equally or more intensely than frozen sections. The two MAbs that showed weaker staining still gave good staining on paraffin sections. Paraffin-embedded rat and mouse eyes were easier to section serially than frozen eyes, showed superior morphology, and individually stained cells were readily identified. Therefore, a combination of PLP fixation and low-temperature paraffin embedding permits detection of the major types of immune cell in rat and mouse tissues while maintaining good morphology, particularly in diseased, damaged, or delicate tissues.

Ocular infection with herpes simplex virus in several strains of rat

PURPOSE

To assess the suitability of the rat for studies of ocular infection with herpes simplex virus (HSV).

METHODS

LEW, AO, DA, PVG, and (DAxLEW)F1 x LEW backcross generation rats, 7 to 9 weeks of age, were inoculated with HSV-1 McKrae. The course of primary disease was assessed by clinical observation using a slit lamp. Infectious virus was assayed in ocular and nervous tissue, and the incidence of latent infection was determined.

RESULTS

LEW and AO strains were the most susceptible. All LEW rats died after an inoculum of 4 x 10(2) plaque-forming units (pfu) and developed severe corneal disease and uveitis. In contrast, all PVG rats survived 10(4) pfu, 60% survived 4 x 10(4) pfu, and eye disease was restricted to epithelial lesions, sometimes accompanied by mild stromal haze. This resolved, even in animals that developed central nervous system disease. The DA strain showed intermediate susceptibility. Resistance was dominant because disease in backcross generation (DA x LEW)F1 x LEW rats resembled that of the DA rather than the LEW strain. Resistance appeared to be linked to coat color (P < 0.001) rather than to major histocompatibility complex (MHC) type. Chronic stromal disease did not occur in survivors (DA, PVG, and hybrid strains only).

CONCLUSIONS

The susceptibility of rat strains to infection of the cornea with HSV varies, and, as with mice, resistance seems to be controlled by non-MHC genes. Rats may prove useful for immunologic studies. Virus reactivation will be the subject of a future report.

Absence of tolerance to noninherited maternal transplantation antigens expressed on skin and cornea

Tolerance to noninherited maternal antigens (NIMAs) of the MHC was investigated in a rat model involving both skin and corneal transplants. Recipient animals were obtained by backcrossing F1 hybrids to parental strain animals. In one group of experiments, crosses were (DA[RT1a] x LEW[RT1(1)]) female-to-LEW male and, in a second group, (DAxPVG[RT1c]) female-to-PVG male. Homozygous backcross offspring (RT1(1/1) or RT1c/c) were putatively tolerant to DA NIMAs if the mother was a hybrid animal, having been exposed to these antigens in utero. The equivalent offspring of hybrid fathers, i.e., LEW female x (DAxLEW) male or PVG female x (DAxPVG) male, served as putatively nontolerant controls. Hemagglutinating antibody levels were measured against the class I RT1Aa antigen on days 7 and 14 after up to three consecutive subcutaneous DA strain skin grafts. Significantly lower titers were found in the putatively tolerant group 7 days after the first skin graft in the RT1a-to-RT1(1) combination (P < 0.05). Levels were not significantly different at any other time point, or at any time point in the RT1a-to-RT1c combination. Tolerance to a corneal graft was not demonstrated in either the strongly rejecting RT1a-to-RT1(1) combination or weakly rejecting RT1a-to-RT1c, whether or not animals were presensitized to RT1a antigens with DA skin grafts. We conclude that tolerance to NIMAs is unimportant in this clinical rat model of transplantation.

Effect of mismatches for major histocompatibility complex and minor antigens on corneal graft rejection

The importance of minor histocompatibility genes in corneal graft rejection was investigated using a model that simulates the major histocompatibility complex (MHC) and minor mismatches of the human allograft more accurately than previous animal models. DA(RT1a) x LEW(RT1(1]F1 hybrid rats were backcrossed to LEW, and the backcross generation were used as corneal graft recipients. Female DA(RT1a) strain animals were used as donors throughout. As in humans, the MHC disparity (a to 1) between each donor-recipient pair could be controlled; minor mismatches were variable and unknown. The MHC haplotype of each backcross individual (either homozygous l/l) or heterozygous a/l) was determined. Depending on this haplotype, the transplanted DA cornea was either matched or mismatched with the recipient for MHC antigens. The average proportion of minor disparate loci was 50%, although this was variable and unknown from recipient to recipient. Some animals of each MHC type were sensitized with three subcutaneous DA strain skin grafts at intervals of 2 weeks. Prior sensitization caused more rapid corneal graft rejection in both MHC mismatched (P less than 0.001) and matched (P less than 0.01) animals. All animals in the two MHC-mismatched groups (sensitized, 26; unsensitized, 17) and most in the MHC-matched groups (sensitized, 25 of 27; unsensitized, all 13) rejected their grafts. The MHC matching resulted in a greater range of survival times, although the difference in survival in unsensitized animals between matched and mismatched groups was not significant (unsensitized, P greater than 0.05; sensitized, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Quantification of herpes simplex virus infection in cervical ganglia of mice

Mice were inoculated with herpes simplex virus (HSV) type 1 in the skin of the neck. The extent of primary and latent infection in the second and third cervical ganglia was investigated. Immunoperoxidase staining of ganglia during primary infection demonstrated HSV antigens initially in a restricted area of the ganglion. By the 5th day after infection, antigen was more widespread. Such a change in the staining pattern is explicable in terms of the zosteriform spread of virus from neurons innervating the site of infection to others supplying other areas of the dermatome. A maximum of approximately 10% of neurons became infected. By the 7th day staining was limited to a few cells. During latent infection, enzymic disaggregation of ganglia followed by immunoperoxidase staining or infectious centre assay indicated that virus reactivation began within 30 h of removal of ganglia and occurred in approximately 1% of viable neurons.