Creating effective biocontainment facilities and maintenance protocols for raising specific pathogen-free, severe combined immunodeficient (SCID) pigs

Severe combined immunodeficiency (SCID) is defined by the lack of an adaptive immune system. Mutations causing SCID are found naturally in humans, mice, horses, dogs, and recently in pigs, with the serendipitous discovery of the Iowa State University SCID pigs. As research models, SCID animals are naturally tolerant of xenotransplantation and offer valuable insight into research areas such as regenerative medicine, cancer therapy, as well as immune cell signaling mechanisms. Large-animal biomedical models, particularly pigs, are increasingly essential to advance the efficacy and safety of novel regenerative therapies on human disease. Thus, there is a need to create practical approaches to maintain hygienic severe immunocompromised porcine models for exploratory medical research. Such research often requires stable genetic lines for replication and survival of healthy SCID animals for months post-treatment. A further hurdle in the development of the ISU SCID pig as a biomedical model involved the establishment of facilities and protocols necessary to obtain clean SPF piglets from the conventional pig farm on which they were discovered. A colony of homozygous SCID boars and SPF carrier sows has been created and maintained through selective breeding, bone marrow transplants, innovative husbandry techniques, and the development of biocontainment facilities.

Expression of H3N2 nucleoprotein in maize seeds and immunogenicity in mice

Oral administration of maize-expressed H3N2 nucleoprotein induced antibody responses in mice showing the immunogenicity of plant-derived antigen and its potential to be utilized as a universal flu vaccine. Influenza A viruses cause influenza epidemics that are devastating to humans and livestock. The vaccine for influenza needs to be reformulated every year to match the circulating strains due to virus mutation. Influenza virus nucleoprotein (NP) is a multifunctional RNA-binding protein that is highly conserved among strains, making it a potential candidate for a universal vaccine. In this study, the NP gene of H3N2 swine origin influenza virus was expressed in maize endosperm. Twelve transgenic maize lines were generated and analyzed for recombinant NP (rNP) expression. Transcript analysis showed the main accumulation of rNP in seed. Protein level of rNP in T1 transgenic maize seeds ranged from 8.0 to 35 µg of NP/g of corn seed. The level increased up to 70 µg of NP/g in T3 seeds. A mouse study was performed to test the immunogenicity of one line of maize-derived rNP (MNP). Mice were immunized with MNP in a prime-boost design. Oral gavage administration showed that a humoral immune response was elicited in the mice treated with MNP indicating the immunogenicity of MNP. NP-specific antibody responses in the MNP group showed comparable antibody titer with the groups receiving positive controls such as Vero cell-derived NP (VNP) or alphavirus replicon particle-derived NP (ANP). Cytokine analysis showed antigen-specific stimulation of IL-4 cytokine elicited in splenocytes from mice treated with MNP further confirming a TH2 humoral immune response induced by MNP administration.

Expression of the cholera toxin B subunit (CT-B) in maize seeds and a combined mucosal treatment against cholera and traveler's diarrhea

The non-toxic B subunit (CT-B) of cholera toxin from Vibrio cholerae is a strong immunogen and amplifies the immune reaction to conjugated antigens. In this work, a synthetic gene encoding for CT-B was expressed under control of a γ-zein promoter in maize seeds. Levels of CT-B in maize plants were determined via ganglioside dependent ELISA. The highest expression level recorded in T(1) generation seeds was 0.0014% of total aqueous soluble protein (TASP). Expression level of the same event in the T(2) generation was significantly increased to 0.0197% of TASP. Immunogenicity of maize derived CT-B was evaluated in mice with an oral immunization trial. Anti-CTB IgG and anti-CTB IgA were detected in the sera and fecal samples of the orally immunized mice, respectively. The mice were protected against holotoxin challenge with CT. An additional group of mice was administrated with an equal amount (5 μg per dose each) of mixed maize-derived CT-B and LT-B (B subunit of E. coli heat labile toxin). In the sera and fecal samples obtained from this group, the specific antibody levels were enhanced compared to either the same or a higher amount of CT-B alone. These results suggest that a synergistic action may be achieved using a CT-B and LT-B mixture that can lead to a more efficacious combined vaccine to target diarrhea induced by both cholera and enterotoxigenic strains of Escherichia coli.

Synthesis and characterization of deoxynivalenol glucuronide: its comparative immunotoxicity with deoxynivalenol

Deoxynivalenol (DON) is a mycotoxin commonly contaminating wheat, barley and corn. DON glucuronide (DONGLU) is a major DON metabolite. We synthesized and purified DONGLU and tested its immunotoxicity, hypothesizing that DONGLU would be much less toxic to K562 cells compared with DON. DONGLU was synthesized using rat liver microsomes, uridine-5'-diphosphoglucuronic acid and DON, and purified with a Sephadex LH-20 column and reverse phase HPLC. beta-Glucuronidase hydrolysis formed a product with retention time and UV spectrum identical with DON. Using atmospheric pressure chemical ionization in negative mode, the molecular mass (M-1) of purified DONGLU was 471 g/mol; in agreement with an expected molecular weight of 472 g/mol. MS and NMR indicated that the glucuronide moiety was conjugated with the carbon-3-hydroxyl group of DON. The cytotoxicity of DON and DONGLU were compared in cell culture using human erythroleukemia cell line K562. Fifty percent inhibition of cell number was observed with a DON concentration of 1.31 microM using a methylthaizol tetrazolium (MTS) cell viability assay whereas no significant cytotoxicity was observed for DONGLU at up to 270 microM. DONGLU did not influence DON toxicity at 0.5 microM, 1.3 microM and 8.4 microM concentration combinations of each compound. These data verified that DONGLU is a detoxification product of DON.

Analysis of Immune Response in Young and Aged Mice Vaccinated With Corn-Derived Antigen Against Escherichia coli Heat-Labile Enterotoxin

Enterotoxigenic strains of Escherichia coli produce a heat-labile holotoxin (LT), which causes diarrhea. We engineered corn seeds to produce LT-B, the nontoxic subunit of LT, to serve as a plant-derived vaccine to traveler's diarrhea and as an adjuvant for co-administered proteins. We previously demonstrated that a strong mucosal and systemic antibody response is elicited in young mice with oral administration of corn-derived LT-B. The present study examined systemic and mucosal antibody responses to LT-B in young and aged mice, and recall responses to oral administration and injection of LT-B in aged mice. Specific IgA and IgG antibodies were detectable during an 11-mo period, although the concentration of antigen-specific antibodies declined gradually. Booster by feeding or injection dramatically increased the concentration of specific IgA from that seen in young mice. Specific IgG levels were boosted to concentrations similar to those in young mice. This effect may be age-dependent and related to prior immunization exposure. Analysis of the antibody response of naïve aged mice against corn-derived LT-B demonstrated an age-related suppression in specific IgG production, but not specific IgA. These results may provide important information for edible vaccine strategies for young and aged individuals.

The role of supplementary dietary antioxidants on immune response in puppies

The objective of this study was to evaluate the effect of supplementary antioxidants (AOX) and whey protein on the immune function health of puppies. Four groups of 10 puppies were fed a control and 3 different test foods (control + antioxidants (AOX), control + AOX + 1% whey protein, and a grocery brand (low AOX)) for 6 weeks. A standard vaccination protocol with a combination canine parvovirus (CPV) and distemper (CDV) vaccine was carried out at 2 and 4 weeks. The results showed that animals on high AOX foods had significantly increased titers, memory cells and serum E concentrations compared to the control and groc groups respectively.

A functional antigen in a practical crop: LT-B producing maize protects mice against Escherichia coli heat labile enterotoxin (LT) and cholera toxin (CT)

We have produced a functional heat labile enterotoxin (LT-) B subunit of Escherichia coli in maize. LT-B is a multimeric protein that presents an ideal model for an edible vaccine, displaying stability in the gut and inducing mucosal and systemic immune responses. Transgenic maize was engineered to synthesize the LT-B polypeptides, which assembled into oligomeric structures with affinity for G(M1) gangliosides. We orally immunized BALB/c mice by feeding transgenic maize meal expressing LT-B or non-transgenic maize meal spiked with bacterial LT-B. Both treatments stimulated elevated IgA and IgG antibodies against LT-B and the closely related cholera toxin B subunit (CT-B) in serum, and elevated IgA in fecal pellets. The transgenic maize induced a higher anti-LT-B and anti-CT-B mucosal and serum IgA response compared to the equivalent amount of bacterial LT-B spiked into maize. Following challenge by oral administration of the diarrhea inducing toxins LT and CT, transgenic maize-fed mice displayed reduced fluid accumulation in the gut compared to non-immunized mice. Moreover, the gut to carcass ratio of immunized mice was not significantly different from the PBS (non-toxin) challenged control group. We concluded that maize-synthesized LT-B had features of the native bacterial LT-B such as molecular weight, G(M1) binding ability, and induction of serum and mucosal immunity. We have demonstrated that maize, a major food and feed ingredient, can be efficiently transformed to produce, accumulate, and store a fully assembled and functional candidate vaccine antigen.

Protein kinase C in rod outer segments: effects of phosphorylation of the phosphodiesterase inhibitory subunit

The inhibitory subunit (PDE gamma) of the cGMP phosphodiesterase (PDE alpha beta gamma 2) in rod outer segments (ROS) realizes its regulatory role in phototransduction by inhibition of PDE alpha beta catalytic activity. The photoreceptor G-protein, transducin, serves as a transducer from the receptor (rhodopsin) to the effector (PDE) and eliminates the inhibitory effect of PDE gamma by direct interaction with PDE gamma. Our previous study [Udovichenko, Cunnick, Gonzalez and Takemoto (1994) J: Biol. Chem. 269, 9850-9856] has shown that PDE gamma is a substrate for protein kinase C (PKC) from ROS and that phosphorylation by PKC increases the ability of PDE gamma to inhibit PDE alpha beta catalytic activity. Here we report that transducin is less effective in activation of PDE alpha beta (gamma p)2 (a complex of PDE alpha beta with phosphorylated PDE gamma, PDE gamma p) than PDE alpha beta gamma 2. PDE gamma p also increases the rate constant of GTP hydrolysis of transducin (from 0.16 S-1 for non-phosphorylated PDE gamma to 0.21 s-1 for PDE gamma p). These data suggest that phosphorylation of the inhibitory subunit of PDE by PKC may regulate the visual transduction cascade by decreasing the photoresponse.

Acridine orange differential staining of total DNA and RNA in normal and galactosemic lens epithelial cells in culture using flow cytometry

The lens epithelial cells are a primary site of involvement in galactosemia. Changes in their size, shape and proliferative capacity have been observed upon exposure to high galactose. In this report, changes in the cell cycle pattern of normal and galactosemic lens epithelial cells were examined by use of flow cytometry. Both changes in DNA and RNA were observed using the fluorochrome, acridine orange. Under the appropriate conditions acridine orange can be used to differentiate double-stranded DNA from single-stranded RNA. Using this approach, the DNA and RNA of normal and galactosemic (1, 4, or 7 days) lens epithelial cells can be compared. The results indicate that lens epithelial cells, when exposed to 40 mM galactose media or 30 mM glucose for 7 days, are induced to enter mitosis. Mannitol did not mimic these results. Changes in the cell cycle pattern were not observed when the cells were treated for 1 or 4 days. Although higher numbers of cells in mitosis were observed after 7 days exposure to 40 mM galactose, a correlation between proliferation, as measured by 3H-thymidine uptake, and mitosis was not possible. Apoptosis was evaluated as a possible explanation for these results. The changes in the DNA staining pattern could be use to monitor lens epithelial cells during galactosemia.

Functional effect of phosphorylation of the photoreceptor phosphodiesterase inhibitory subunit by protein kinase C

In rod outer segments the light activation of cGMP phosphodiesterase (PDE alpha beta gamma 2) is accomplished by removal of the gamma inhibitory subunit (PDE gamma) from the PDE alpha beta catalytic subunits. A light activation of the inositol signaling pathway also occurs, but there is little information linking these two signal transduction pathways. Here we report that protein kinase C (PKC) purified from bovine rod outer segment phosphorylates the bovine PDE gamma with incorporation of 0.9 +/- 0.1 mol of phosphate/mol of PDE gamma. Phosphorylation of PDE gamma increases its ability to inhibit PDE alpha beta catalytic activity (trypsin-activated PDE, tPDE) with an IC50 for phosphorylated PDE gamma of 26 +/- 4 pM and an IC50 of 60 +/- 5 pM for unphosphorylated PDE gamma. Inhibition of tPDE by PDE gamma is characterized by two values of Kd, Kd1 = 34 pM and Kd2 = 760 pM. Phosphorylation of PDE gamma by PKC eliminates the functional heterogeneity of the PDE gamma population resulting in a single value of Kd = 23 pM. Free PDE gamma (without PDE alpha beta catalytic subunits) is a better substrate for PKC than PDE gamma in a complex with PDE alpha beta. Phosphorylation of free PDE gamma by PKC is characterized by a value of Vmax = 1,550 +/- 148 units/mg (Km = 21.0 +/- 1.9 microM). In contrast, phosphorylation of PDE gamma in PDE alpha beta gamma 2 complex has two values of Vmax, Vmax1 = 0.3 +/- 0.1 units/mg of PDE gamma (Km1 = 0.4 +/- 0.2 microM) and Vmax2 = 0.7 +/- 0.2 units/mg of PDE gamma (Km2 = 4.6 +/- 0.9 microM). ROS PKC phosphorylates Thr35 in PDE gamma. We have previously reported (Morrison, D. F., Rider, M. A., and Takemoto, D. J. (1987) FEBS Lett. 222, 266-270; Lipkin, V. M., Udovichenko, I. P., Bodarenko, V. A., Yurovskaya, A. A., Telnykh, E. V., and Skiba, N. P. (1990) Biomed. Sci. (Lond.) 1, 305-308) that the central fragment of PDE gamma (24-45) is responsible for binding to PDE catalytic subunits. The new data suggests that this region of PDE gamma also includes the site for phosphorylation by PKC and that phosphorylation increases the ability of PDE gamma to inhibit PDE catalytic activity. This altered regulation of visual transduction may play a role in desensitization or light adaptation.

Identification of a binding site on retinal transducin alpha for the phosphodiesterase inhibitory gamma subunit

Transducin alpha (T alpha) activates retinal rod cyclic GMP phosphodiesterase (PDE) by interacting with and removing the inhibitory PDE gamma subunit. A T alpha-PDE gamma complex can be isolated in vitro, and our previous work [Morrison, Rider and Takemoto (1987) FEBS Lett. 222, 266-270; Morrison, Cunnick, Oppert and Takemoto (1989) J. Biol. Chem. 264, 11671-11681] has identified a region of PDE gamma, residues 24-45, that binds to T alpha. The C-terminal region of PDE gamma is the site that interacts with PDE alpha/beta and inhibits catalytic function. The site on T alpha that binds to the PDE gamma 24-45 region has not been identified. Synthetic peptides (15-mers) which span the bovine T alpha sequence were tested for binding to purified recombinant PDE gamma using a solid-phase assay. The peptides were also tested for ability to activate a PDE complex. We have identified a region, residues 250-275 of T alpha, which shows a high affinity of PDE gamma and for the PDE gamma (24-45) binding peptide. The peptide did not bind to the C-terminal residues 50-87 of PDE gamma. Likewise, a region of T alpha, 1-25 did not exhibit high-affinity binding to PDE gamma or to the 24-45 PDE gamma peptide. Specific binding of the 250-275 peptide to PDE gamma was confirmed by its ability to compete with T alpha binding to PDE gamma, although a higher concentration was required (10x). The T alpha-(250-275) peptide activated a fully inhibited PDE alpha beta gamma 2 complex in a dose-dependent manner. These results suggest that a region on T alpha that recognizes the PDE gamma-binding site is found within residues 250-275 of T alpha.

Phosphorylation of bovine rod photoreceptor cyclic GMP phosphodiesterase

The cyclic GMP phosphodiesterase (PDE) of retinal rods plays a key role in phototransduction and consists of two catalytic subunits (PDE alpha and PDE beta) and two identical inhibitory subunits (PDE gamma). Here we report that PDE alpha and PDE gamma are phosphorylated by protein kinase(s) C (PKC) from brain and rod outer segments (ROS). These same two types of PKC also phosphorylate PDE alpha in trypsin-activated PDE (without PDE gamma). In contrast, cyclic-AMP-dependent protein kinase catalytic subunit phosphorylates both PDE alpha and PDE beta, but not PDE gamma. This kinase does not phosphorylate trypsin-activated PDE. The synthetic peptides AKVISNLLGPREAAV (PDE alpha 30-44) and KQRQTRQFKSKPPKK (PDE gamma 31-45) inhibited phosphorylation of PDE by PKC from ROS. These data suggest that sites (at least one for each subunit) for phosphorylation of PDE by PKC are localized in these corresponding regions of PDE alpha and PDE gamma. Isoenzyme-specific PKC antibodies against peptides unique to the alpha, beta, gamma, delta, epsilon and zeta isoforms of protein kinase C were used to show that a major form of PKC in ROS is PKC alpha. However, other minor forms were also present.

Protein kinase C in galactosemic and tolrestat-treated lens epithelial cells

Using isozyme-specific anti-peptide antisera against peptides from the alpha-, beta-, gamma-, delta-, epsilon-, and zeta-isoforms of brain protein kinase C (PKC), we have identified proteins in bovine lens epithelial cells, in culture, that were reactive with these antisera. Western blots of lens epithelial cell homogenates showed that PKC-alpha antisera reacted with a major protein, and PKC-gamma antisera reacted with a minor protein. When the lens epithelial cells were cultured in media supplemented with 40 mM galactose, to model the conditions of sugar cataracts, a decrease in PKC-gamma, but not in PKC-alpha was observed. These were normalized if the cells were cultured in 40 mM galactose media supplemented with an inhibitor of aldose reductase, Tolrestat (10 microM). These results suggest that changes in PKC isoforms occur in the galactosemic diabetic state.

Carriers of the mouse rd gene have reduced levels of the beta subunit of the retinal cyclic GMP phosphodiesterase

Polyclonal antipeptide antisera have been utilized to quantitate the amount of retinal rod outer segment cGMP phosphodiesterase alpha and beta catalytic subunits present in retinas from C57BL/6J mice which are normal or carriers for the rd gene defect. Results suggest that the quantity of PDE-beta subunit is reduced in carrier mice while PDE-alpha and PDE-gamma are not affected. In 21-day-old mice, the PDE-beta was reduced by about one-half while adult carrier mice had even more reduced levels of PDE-beta. Since PDE alpha was not reduced, this suggests that synthesis of PDE alpha and PDE beta may not be coordinately controlled.

Domain mapping of the retinal cyclic GMP phosphodiesterase gamma-subunit. Function of the domains encoded by the three exons of the gamma-subunit gene

Retinal rod-outer-segment phosphodiesterase (PDE) is a heterotetramer consisting of two similar, but not identical, catalytic subunits (alpha and beta) and two identical inhibitory subunits (gamma 2). Previously, we have reported that the site of PDE alpha/beta interaction with PDE gamma is located within residues 54-87 [Cunnick, Hurt, Oppert, Sakamoto & Takemoto (1990) Biochem. J. 271, 721-727]. The site for PDE gamma interaction with transducin alpha (T alpha) was found to encompass residues 24-45 of PDE gamma [Morrison, Cunnick, Oppert & Takemoto (1989) J. Biol. Chem. 264, 11671-11681]. In order to identify binding sites and other functional domains of PDE gamma, the three peptides which are encoded by the three exons of the PDE gamma gene were synthesized chemically. These exons encode for residues 1-49, 50-62 and 63-87 of bovine PDE gamma [Piriev, Purishko, Khramtsov & Lipkin (1990) Dokl. Akad. Nauk. SSSR 315, 229-230]. The peptide encompassing residues 63-87 was inhibitory in a PDE assay, whereas peptides 1-49 and 50-62 had no effect. However, both peptides 1-49 and 63-87 bound to PDE alpha/beta in a solid-phase binding assay. Only peptide 1-49 bound to T alpha.GTP[S] (GTP[S] is guanosine 5'-[gamma-thio]triphosphate). These data confirm that the inhibitory region of PDE gamma is encoded by exon 3 (residues 63-87), whereas a separate binding site for PDE alpha/beta and for T alpha.GTP[S] is encoded by exon 1 (residues 1-49). To study further the structure-function relationship of PDE gamma, this entire protein and two mutants were chemically synthesized. One mutant (-CT) lacked residues 78-87, whereas another replaced tyrosine-84 with glycine (TYR-84). Whereas the synthetic PDE gamma inhibited PDE alpha/beta catalytic activity, the -CT and TVR-84 mutants did not. All three synthetic proteins bound to both PDE alpha/beta and and T alpha.GTP[S]. These data confirm the presence of an alternative binding site on PDE gamma and demonstrate the importance of tyrosine-84 in PDE gamma inhibitory activity.

Retinal cyclic-GMP phosphodiesterase gamma-subunit: identification of functional residues in the inhibitory region

Previously, we have domain-mapped the 87 amino acid PDE gamma inhibitory subunit of the retinal phosphodiesterase (PDE) alpha beta gamma 2 complex using synthetic peptides. The PDE gamma subunit has a binding domain for transducin-alpha (T alpha) and for PDE alpha/beta within residues # 24-45 and an inhibitory region for PDE alpha/beta within residues # 80-87. In order to establish the role of individual amino acids in the function of the PDE gamma inhibitory subunit, peptides of PDE gamma # 63-87 and mutant peptides were synthesized and utilized in PDE inhibition assays. The following peptides exhibited a decreased ability to inhibit PDE alpha/beta: All were from PDE gamma # 63-87; PDE gamma Tyr 84----Gly, PDE gamma Phe 73----Gly and PDE gamma Gln 83----Gly.

Retinal cyclic-GMP phosphodiesterase gamma-subunit: use of mutant synthetic peptides to define function

Previously, we have domain-mapped the 87 amino acid PDE gamma inhibitory subunit of the retinal phosphodiesterase (PDE) alpha beta gamma 2 complex using synthetic peptides (1). The PDE gamma subunit has a binding domain for transducin-alpha (T alpha) and for PDE alpha/beta within residues #24-45. An inhibitory region for PDE alpha/beta is within residues #80-87. In order to establish the role of individual amino acids in the function of the PDE gamma inhibitory subunit, mutants were synthesized and utilized in PDE inhibition assays. The following mutants exhibited a decreased ability to inhibit PDE alpha/beta: Tyr84----Gly; Arg24----Gly; and Arg33----Pro. Sequence comparisons with cone PDE gamma indicate that there is identity within these functional regions.

Rod/cone dysplasia in Irish setters. Presence of an altered rhodopsin

On the basis of the amino acid sequence of bovine rhodopsin, a series of peptides from the C-terminus (Rhod-4 and Rhod-1) and external loops (Rhod-10) were synthesized. Rabbit antisera to these peptides recognize the rhodopsin molecule in whole retina from 8-week-old normal and affected rcdl (rod/cone-dysplasic) Irish setters (8- and 4-weeks-old). When the rhodopsin content was equalized by using a solid-phase radioimmunoassay, the reaction with anti-peptide antisera to the C-terminal octapeptide (residues 341-348) is severely decreased in the rcdl-dog retinas. The results of mixing experiments suggest that this is not due to proteolytic clipping of the rhodopsin C-terminus from the affected dogs. Treatment of retinas with 1.0 mM-NaF, a phosphatase inhibitor, or pretreatment with alkaline and acid phosphatases does alter the reaction of the rhodopsin with anti-rhodopsin antisera. This suggests that the decreased reaction of the affected rhodopsin with the anti-peptide antisera may partially result from differences in intrinsic rhodopsin phosphorylation. However, since the reaction of rcdl retinas cannot be restored to that of the normals, these results suggest that the rhodopsin molecule from the rcdl dogs may be structurally altered in other ways.

Reduced rhodopsin phosphorylation during retinal dystrophy

During inherited retinal dystrophy in Irish Setter dogs, decreased activity of cGMP phosphodiesterase (PDE) results in high cGMP levels and retinal degeneration (1-3). This defect could be in PDE itself, or in its interactions with other proteins of the rod outer segment. We report herein that when retinas from 8-week-old dogs were phosphorylated with gamma-32P-ATP, and separated on SDS-PAGE, phosphorylation of rd dog rhodopsin was reduced. When rd retinas were mixed with normal dog retinas, phosphorylation of the latter was inhibited. Since rd-mediated inhibition was prevented by 1 mM NaF, the results suggest that the cause of reduced rd phosphorylation is increased phosphatase activity. Together, these results demonstrate that decreased phosphorylation of rhodopsin due to increased phosphatase activity is a fundamental biochemical change which may partially account for the degenerative process and loss of visual acuity during inherited retinal dystrophy.