Immunohistochemistry Studies of Tumor Necrosis Factor Αlpha and Interferon Gamma Expression in Pseudocapillaria tomentosa Infected and Uninfected Zebrafish By Lalee C. Lo An Undergraduate Thesis Submitted to Oregon State University In partial fulfillment of the requirements for the degree of Baccalaureate of Science in BioResource Research, Food Science Option and Chemistry Minor September 02, 2009 1 Signature Page: APPROVED: _________________________________ Jan Marie Spitsbergen faculty mentor, department _______________ Date _________________________________ Susan Tornquist secondary mentor, department _______________ Date _________________________________ Katharine G. Field, BRR Director _______________ Date © Copyright by Lalee C. Lo September 02, 2009 All rights reserved I understand that my project will become part of the permanent collection of the Oregon State University Library, and will become part of the Scholars Archive collection for BioResource Research. My signature below authorizes release of my project and thesis to any reader upon request. _________________________________ Lalee C. Lo _______________ Date 2 Immunohistochemistry Studies of Tumor Necrosis Factor Αlpha and Interferon Gamma Expression in Pseudocapillaria tomentosa Infected and Uninfected Zebrafish Lalee Lo Department of Microbiology, Oregon State University, Corvallis, Oregon, USA ABSTRACT Tumor necrosis factor alpha (TNF α) and interferon gamma (IFN γ) were initially recognized as inflammatory mediators produced by immune cells in response to infectious agents or foreign material. (1,5) However, over the past decade much research in mammalian species has indicated that these proteins also play key roles in development and homeostasis of many tissues such as adipose tissue and endocrine islets of pancreas (2,3,12). Our goal was to determine whether the levels of these mediators were elevated in tissues of zebrafish following infection with intestinal nematodes. We examined protein expression for these mediators in whole histologic sections of zebrafish using immunohistochemistry applied to uninfected fish and fish infected with the intestinal nematode Pseudocapillaria tomentosa. Fish were sampled for histologic study at selected time points following infection with the nematodes. We utilized commercially available antibodies to mammalian TNF α and IFN γ and the DAKO Envision Plus Immunohistochemistry polymer system for detection of these proteins in fish tissues. Contrary to our initial hypothesis that parasite infected fish would have increased levels of these inflammatory mediators in tissues, we found no overall increase in these mediators in parasite infected fish using immunohistochemistry at the 12 week post-infection sample point. However, the early 5 week post-infection sample point showed that there was an increase in the levels of these mediators in parasite infected fish. Similar with observations in mammals that these mediators play important roles in tissue development and homeostasis, we found consistent, specific, moderate to strong 3 baseline expression of these mediators in several tissues of zebrafish. In assays conducted at 5 weeks following parasite infection we saw increased levels of TNF α and IFN γ in inflamed skeletal muscle and saw increased TNF α in segments of bowel in which recent inflammation occurred. INTRODUCTION The purpose of these experiments was to investigate the expression of two cytokines, TNF α and IFN γ, in zebrafish following infection. TNF α and IFN γ are important signaling molecules that are vital to immune regulation; although they also play roles in many other functions (6,7). The human body has natural defense mechanisms that protect against invading pathogens such as bacteria, fungus, and viruses. An important component of these innate defense mechanisms are white blood cells or leukocytes (10). The word leukocyte is a broad term that refers to two classes of cells: granulocyte and agranulocyte. In each class there are different types of cells (Fig. 1); for example, in mammals there are three types of granulocytes: neutrophils, basophils, and eosinophils. But zebrafish are different from mammals in having a cell with combined characteristics of both eosinophil and basophil called the eosinophil/basophil. The agranulocytes include lymphocytes, monocytes, and macrophages in both mammals and fish (15). 4 Figure 1. Types of Leukocytes (http://www.newworldencyclopedia.org/entry/Leukocyte) Each type of leukocyte can produce cytokines, including TNF α and IFN γ, which can then be used as signaling molecules for the autocrine, paracrine, and endocrine communication systems. The autocrine system only affects the cell itself and/or like cells; the paracrine system affects the cells around the cell regardless of type; the endocrine system affects all cells and functions in growth, development, metabolism, and function (15,16). The zebrafish was used in our experiments as it is a powerful model organism to study disease mechanisms. Zebrafish are ideal for gene knock out studies, as the knocking out of some genes in mammal embryos will lead to embryo mortality. Because of a whole genome duplication that occurred in ancestors of bony fish, but not tetrapods, zebrafish often have duplicate genes for mammalian orthologs. An inactivating mutation of one of these genes may still allow development of live embryos, while a mutation in the mammalian ortholog is embryonic lethal. Zebrafish also develop several immune cells homologous to the mammalian counterparts, including lymphocytes, monocyte/macrophages, and neutrophils; these also produce the cytokines known as TNF α and IFN γ (11,18). This makes zebrafish ideal, as they are easy to maintain and keep in high numbers. The experiment involved the tissue sampling of uninfected zebrafish and Pseudocapillaria tomentosa infected zebrafish with the use of immunohistochemistry; this was used to aid in the visualization of the intensity of the TNF α and IFN γ cytokines. Pseudocapillaria tomentosa is a common gut nematode of fish previously used in Dr. Jan Marie Spitsbergen’s laboratory and was 5 known to cause inflammation in the gut and intestine of zebrafish; infection by this nematode also leads to the formation of aggressive neoplasm of the intestine. However, because the narrow sampling window in the original experimental group did not reveal changes in TNF α and IFN γ expression, a second set of tissue slides with earlier sample times was also analyzed. This group of zebrafish was exposed to a carcinogen, DMBA (7,12dimethylbenz[a]anthracene) with a DMSO (dimethylsulfoxide 0.1%) carrier in three protocols, bath exposure of embryos, bath exposure of fry, and dietary exposure of juveniles at a concentration of 1.0 ppm; the carcinogen also induced neoplasia (14). We also investigated MPO expression in uninfected and infected zebrafish. Myeloperoxidase (MPO) specifically stains the cytoplasm of neutrophils of zebrafish and helped determine the sites of inflammation and severity (4). Our hypothesis was that Pseudocapillaria tomentosa infected zebrafish would have stronger staining of tissues with chromogen in immunohistochemistry studies compared to uninfected zebrafish, indicating elevated tissue levels of TNF α and IFN γ. The study has great potential importance because it could cast light on current and future research on the function of TNF α and IFN γ. MATERIALS AND METHODS Zebrafish We maintained a tank of parasite donor fish holding fish infected with Pseudocapillaria tomentosa. Juvenile fish were used to keep the disease cycling so adults would not develop immunity and shed the parasites. Zebrafish were raised in flowing well water in 30 gallon tanks at 6 27 Celsius +/- 2 degrees and fed ad libitum daily with Aquatox flake fish feed (Ziegler, Gardners PA), a diet in which the fish meal component is pretested to ensure minimal levels of natural carcinogens and nitrosamines. Brine shrimp were also fed daily. The feeding schedule was setup to prevent contamination to the non-infected zebrafish; this was accomplished by feeding the noninfected zebrafish first and then feeding the infected zebrafish last, and using separate containers for uninfected and infected fish. Tank algae and waste feed were removed weekly. Table 1: Experimental Design for Study of Interaction of Gut Nematodes Date of Birth Date of Carcinogen Exposure Carcinogen Treatment Date of Parasite Treatment Parasite Treatment Lot # 1/5/06 2/8/06 (age 30 days) DMSO Control 3/20/06 None ZRN 14-5 1/5/06 2/8/06 (age 30 days) DMSO Control 3/20/06 Pseudoca pillaria ZRN 145b 1/5/06 2/8/06 (age 30 days) DMBA 1 ppm 3/20/06 None ZRN 14-6 1/5/06 2/8/06 (age 30 days) DMBA 1 ppm 3/20/06 Pseudoca pillaria ZRN 146b ZRN 14-9 ZRN 1410 ZRN 14- 9/10/0 6 9/10/0 6 9/10/0 6 None None 5/10/2007 Pseudoca pillaria None None 5/10/2007 Pseudoca pillaria None None 5/10/2007 None Sampling for Histology and Immunohistochemistry 5 fish at 3 wk and 5 wk, 20 fish at 17 wk, 30-50 fish at 29 wk post-parasite 5 fish at 3 wk and 5 wk, 20 fish at 17 wk, 30-50 fish at 29 wk post-parasite 5 fish at 3 wk and 5 wk, 20 fish at 17 wk, 30-50 fish at 29 wk post-parasite 5 fish at 3 wk and 5 wk, 20 fish at 17 wk, 30-50 fish at 29 wk post-parasite # of Fish 8/10/2007 20 8/10/2007 20 8/10/2007 20 74 67 74 90 7 9/10/0 6 None None 5/10/2007 None 11 ZRN 1412 8/10/2007 20 Experimental Tank Setup Table 1 shows the experimental setup. A total of 8 parasite donors were placed into a plastic mesh cylinder secured to the side of the tank for each tank for parasite transmission. Each treatment group, ZRN 14-9 to 14-12, contained 20 zebrafish; all were sampled at 11 months after the date of birth and 12 weeks post infection. The sampling was performed by using a lethal dose of MS-222 which was obtained through the Argent Chemical Company; the fish were then transferred to the veterinary diagnostic laboratory of the OSU school of Veterinary Medicine and placed in paraffin blocks. Immunohistochemistry Protocol Procedures Table 2: Immunohistochemistry chemicals used in the experiment. Immunohistochemistry Chemical Description ABCam TNF α Monocolonally derived in rabbits immunized with human TNF alpha. ABCam, Cambridge, MA. The following concentrations using the ABCam antibody diluent: 1/50, 1/100, 1/1000, 1/5000, 1/10000, 1/50,000, 1/100,000. Polycolonally derived in rabbit, ABCam, Cambridge, MA. The following concentrations using the ABCam diluent: 1/100, 1/200, 1/400, 1/1000. Polyclonal antibody derived in rabbits immunized with human neutrophil myeloperoxidase. ABCam, Cambridge, MA. Specifically stains the cytoplasm of neutrophils of zebrafish and helped determine the sites of inflammation and severity. Dako North America, Carpinteria, CA. Used between the binding of the primary and secondary antibodies and also after a peroxidase block to reduce the risk of unspecific binding; the slides were then rinsed 6 times after each binding process. ABCam IFN γ MPO (Myeloperoxidase) A Dako wash buffer (PBST; phosphate buffered saline, pH 7.6, containing 0.01% Tween 20) 8 The zebrafish tissue was obtained through a paraffin sectioning method; this procedure was accomplished by the veterinary diagnostic laboratory of the OSU School of Veterinary Medicine. In brief, the whole zebrafish was set in a block of paraffin wax and then 4 micrometer thick slices were cut and placed onto microscope slides. Immunohistochemistry Slide Preparation The next step was to expose the slides to the immunohistochemistry chemicals (see Table 2); we used an immunohistochemistry (IHC) protocol which was developed in a previous experiment utilizing the Dako Envision Plus immunohistochemistry kit. The slide with the tissue was heated on a hot plate at 37 degrees Celsius for 15-20 minutes. It was then immersed for two treatments in P-xylene for 10 minutes; then placed in 2 treatments of 100% EtOH for 3 minutes each; then washed in 95% EtOH for 3 minutes; and then 3 minutes in 70% EtOH. The slides were dipped 10 times in fresh deionized water and then 10 times in PBST. The slides were then left in the PBST if other slides were to be prepared. Antigen Retrieval For antigen retrieval, we used a steam and enzymatic protocol developed in a previous experiment. After the slides were prepared, they were placed in a plastic slide holder filled with PBST. The container was then heated in a rice cooker filled with water for 20 minutes. The slides were then removed and rinsed in PBST and then set in a Microprobe (a slide holder for specialized Probe On slides which allow solution wicking.) and set in blocking solution (BSA 1%, DMSO 1%, normal goat serum 2% in PBS, pH 7.6) for 30 minutes. The blocking solution prevents nonspecific binding of primary and secondary antibodies to the tissue sections. Primary and Secondary Antibody Application After the antigen retrieval, the slides were then put into the primary antibody and left for 30 minutes. The slides were then washed with PBST and a secondary antibody was applied for a 9 minimum of 30 minutes. The secondary antibody was obtained with the primary antibody in the ABCam kit. Table 2 shows the specific types of antibodies used, their sources and dilutions in the experiment. Negative Controls The negative control slides were prepared identically to the experimental slides, but were not exposed to the primary and secondary antibody; instead they were set in normal rabbit serum, normal mouse serum, and PBST. Negative controls indicate whether there is significant nonspecific tissue binding of non-immune serum of the same species as the primary antibody. Slide Staining and Visualization The slides were then washed with PBST, incubated with chromogen for 20 minutes; then rinsed with deionized water and transferred to deionized water. The slide were briefly stained with hematoxylin in one dip and quickly thoroughly rinsed in water. Slides were then placed on the heater plate set to 80 degrees F and the water allowed toevaporate; afterwards 3 drops of crystal mount were used to cover and protect the stained tissue. The slides were then analyzed using a visual scoring from a scale of 1-3, 1 being light staining and 3 being very heavy staining. RESULTS AND DISCUSSION At the beginning of any immunohistochemistry study, one must optimize the protocol for the procedure and for the specific antibodies to be used. Therefore we tested various factors during the optimization process. We first determined the optimal concentration of antibody to use for each antibody tested, by evaluating a range of dilutions of each antibody. The TNF α and IFN γ antibodies at full concentration caused the antigen to bind too strongly and created too much background. The best result with the ABCam TNF α was with a dilution of 1/10000 since this 10 produced minimal background and optimal specific staining of positive tissues. The best result with the ABCam IFN γ antibody was at a dilution of 1/1000. We then evaluated whether antigen retrieval was required for optimal assay results. Enzymatic antigen retrieval was not helpful with these tissues and antibodies. We compared two methods of antigen retrieval, heat treatment and enzyme treatment of histological sections (19). Steam heat treatment resulted in better staining, so we included it in the final protocol. When we compared various buffers for the steam heat treatment, we found that there was little to no difference in the results; therefore, we decided to use the Dako antigen retrieval buffer. We included a positive control to ensure that the reagents were working. We first did an immunohistochemistry assay for proliferating cell nuclear antibody (PCNA), using a mouse monoclonal antibody to mammal PCNA. This antibody had been validated as reacting strongly with proliferating zebrafish cells in previous assays in Dr. Spitsbergen’s laboratory. We also tried various antibody concentrations to optimize the dilutions. We also investigated MPO expression in uninfected and infected zebrafish. Because the concentration of the prediluted MPO antibody was optimized for mammal tissues, we found that the optimal concentration for use on zebrafish tissue actually was a dilution of 1:2 of this prediluted antibody. After the sampling time, MPO expression was used to determine the severity of the inflammation of the infected and uninfected zebrafish tissue. MPO specifically stains the cytoplasm of neutrophils of zebrafish which are the first responders to these sites of inflammation (10, 15). A 11 comparison of MPO expression in uninfected and infected zebrafish revealed that the intestine of zebrafish chronically infected with Pseudocapillaria tomentosa (12 weeks post infection) showed increased numbers of neutrophils compared to intestine of uninfected fish (Figures 1,2). Reactive oxygen from inflammatory cells such as neutrophils is known to cause damage to proteins and nucleic acid in tissues experiencing chronic infection (4). Specific types of DNA damage are associated with this chronic inflammation and this DNA damage likely plays a role in the neoplasia associated with chronic inflammation. Figure 1: MPO negative in uninfected zebrafish (left photo) and MPO positive in infected zebrafish (right photo). Figure 2: MPO in neutrophils in impression smear from kidney. All negative controls (tissues with no added antibody) showed no staining (Figure 3 and Figure 4) 12 Figure 3: 1.25x mouse serum negative control. Figure 4: 1.25x rabbit serum negative control. In previous experiments, the nematode Pseudocapillaria tomentosa caused the production of tumors in the intestine, and so we expected there to be a higher concentration of TNF α in these areas of inflamed intestinal tissue. Figures 5 and 6, show strong chromogen staining for both inflammatory mediators in several tissues of the zebrafish; these results are summarized in Table 3,4,5. We found the immunity cytokines TNF α and IFN γ to be present in several of the tissues derived from ectoderm, mesoderm, and endoderm. (Figures 7-9) 13 Figure 5: TNF α stain of ZRN 14-5 at 5x magnification. Image of immunohistochemistry with antibody used at a dilution of 1:1000. TNF α reactivity was present in several tissues. Specific positive staining was seen in certain layers of the eye and skeletal muscle of the head. Figure 6: TNF α stain of ZRN 14-5 at 5x magnification. Presence of TNF α was seen in selected tissues in meso and endoderm. Figure 7: Post 5 week infection of TNF α stain of ZRN 5 uninfected intestine (left photo) and TNF α stain of ZRN 5 infected intestine (right photo). TNF α was present at higher levels in the infected tissue. 14 Figure 8: IFN γ revealed by immunohistochemistry of ZRN 14-9 heart at 10x magnification. The red indicated that the cells in the heart contained TNF α. Figure 9: Post 5 week infection of IFNγ in inflamed skeletal muscle of trunk (left photo) and IFNγ in skeletal muscle near optic nerve (right photo). According to our initial hypothesis, the uninfected group should have shown lower concentrations of TNF α and IFN γ due to less gut inflammation; however the visual intensity of inflammatory mediators as indicated by immunohistochemistry was the same for all the treatment groups at the 12 week post infection sample point (Table 3,4,5). We were unable to establish a link between the intensity levels of TNF α and IFN γ in parasite infection at this with the later sampling point. We expected that TNF α and IFN γ production would increase in parasite infected fish as previous studies showed them to be immune response signaling proteins. However, even uninfected zebrafish expressed relatively high levels of these cytokines in certain tissues. (Figure 5) 15 Finally, an earlier experiment treated zebrafish with carcinogen (Table 1), then infected two of the four groups with Pseudocapillaria tomentosa. These slides included earlier sample points (Figure 7) and the results were as expected. The 5 week post-infection TNF α stains indicated that the infected zebrafish inflamed intestine showed elevated levels of TNF α, while the uninfected showed very low levels of TNF α; this also supports the hypothesis. IFN γ at the 5 week postinfection sample point also displayed an increase in the inflamed skeletal muscle on the trunk and near the optic nerve (Figure 9) when compared to the uninfected zebrafish. This also supports the hypothesis that parasite infection does increase the production of IFN γ. Table 3: Summary of Tissues Expressing Protein for Inflammatory Mediators Intensity of Staining: 1+=low; 2+=medium; 3+=high Proteins Expressed Tissue Category Body Region Organ System Organ Tissue Ectoderm Head Skin Sensory organ Eye CNS Ear Nose Taste bud Brain Neuroepithelium Lens Cornea Vestibular neuroepithelium Sensory neuroepithelium Neurons in midbrain and cerebellum Neurons in diencephalon, midbrain, hindbrain Pituitary Optic nerve Trunk Mesoderm Tail Head Gill Pseudobranch Skin Fin Skin Vascular Lymphohemopoietic Surface epithelium Epithelium Skin epithelium Blood vessel Thymus Anterior kidney Abcam TNF α 0 2+ 0 0 Abcam IFN γ 0 2+ 1+ 0 0 0 0 0 2+ 2+ 2+ 1+ 2+ 1+ 0 2+ 1+ 0 0 0 NA NA 2+ 0 0 1+ 0 0 0 NA NA NA NA 0 16 Muscular Skeletal Trunk Gill Cardiovascular Heart Urinary Trunk Kidney Lymphohemopoietic Muscular Trunk Kidney Skeletal Fin Tail Endoderm Head Gastrointestinal Trunk Gastrointestinal Oropharynx Pharyngeal mill Esophagus Pneumatic duct Intestine Gas Bladder Liver Neural Crest Head Skeletal muscle Cartilage Bone Cartilage Bulbus Atrium Ventricle Renal tubules 3+ 3+ 1+ 1+ 1+ 1+ 2+ 2+ 1+ 0 0 0 3+ 3+ 3+ 0 Mesonephric duct Hemopoietic tissue 1+ 1+ 0 2+ Red skeletal muscle White skeletal muscle Cartilage Bone Skeletal muscle Cartilage Skeletal muscle Cartilage Mucosal epithelium 3+ 3+ 1+ 1+ 3+ 1+ 3+ 1+ 1+ 1+ 0 Mucosal epithelium 1+ 1+ 0 0 Anterior intestine near esophagus, mucosal epithelium 1+ 0 Middle mucosal epithelium Posterior mucosal epithelium 1+ 1+ 1+ 2+ 2+ NA 0 0 0 0 0 2+ Hepatocyte Bile duct 8th cranial nerve Cranial nerves 0 0 0 0 0 0 0 0 0 Table 4: Tumor Necrosis Factor Alpha Histochemical Staining Summary. Tissues Staining Strongly Skeletal muscle of head and at bases of fins (derived from neural crest) Intestine mucosal surface (entire intestine) Tissues Staining Moderately Tissues Staining Lightly Neurosensory epithelium of nose Bile duct mucosal surface Taste Buds Exocrine pancreas acinar cell Ultimobranchial gland Chloride cell of gill filament and lamellae Outer plexiform layer of retina of eye 17 Heart ventricular myocardium Heart atrial myocardium Table 5: Interferon Gamma Histochemical Staining Summary. Tissues Staining Strongly Tissues Staining Moderately Endocardium of heart Neurosensory epithelium of nose Taste Buds Macrophages in inflammation in skeletal muscle Inflammatory cells in connective tissue Tissues Staining Lightly Pseudobranch epithelium Ameloblastic epithelium of tooth Hemopoietic tissue in kidney (multifocal) Meninges and ventricles of brain Chloride cells of gill filament Ganglia of cranial nerves Developing oocytes (perinucleolar and vitellogenic) Tooth pulp Our hypothesis, that Pseudocapillaria tomentosa infected zebrafish would have stronger staining of tissues with chromogen in immunohischemistry studies, indicating elevated tissue levels of TNF α and IFN γ, is supported with this research project. However, this was only observed at the 5 weeks post infection sample time. At the later sample time points, uninfected and infected zebrafish showed similar levels of TNF α and IFN γ. This suggests that they may play other roles besides immune cell signaling such as homeostasis. Mammalian data also indicate that these mediators do play essential roles in development and homeostasis of many tissues (12, 13, 17). Improvements to the experiment 18 In the future, the experiment could be improved upon by incorporating a Western blot to clarify the specificity of both of the antibodies. Because TNF α and IFN γ are part of large super-families of related proteins in both mammals and fish, (21) we need to show that the ABCam antibodies bind specifically to the TNF α and IFN γ antigens of zebrafish. In zebrafish there are duplicate IFN γ genes and proteins, (11) so it is important to clarify if the antibody to IFN γ binds to both IFN γ1 and IFN γ2 of zebrafish. The antibodies purchased from ABCam were shown to bind to mouse, guinea pig, human, cynomolgus monkey, and rhesus monkey TNF α and human and rhesus monkey IFN γ, but it is not yet known whether it binds specifically to zebrafish TNF α and IFN γ. Another way to validate the immunohistochemsitry studies would be to look at expression of TNF α and IFN γ in zebrafish tissues using situ hybridization to evaluate RNA expression in the tissues. ACKNOWLEDGEMENTS This work was supported by a National Institutes of Health (NIH) grant from Dr. Jan Marie Spitsbergen, the facilities at the John Fryer Salmon Disease Lab, the Marine and Freshwater Biomedical Science Center, and the Environmental Health Science Center at Oregon State University. 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