Cloning, expression and characterization of biologically active feline tumour necrosis factor-alpha

Development and analytical validation of an enzyme-linked immunosorbent assay for the measurement of feline tumor necrosis factor α in serum

BACKGROUND

The role of tumor necrosis factor alpha (TNF-α), a cytokine shown to play a crucial role in human Crohn's disease patients, has not been documented in cats with chronic enteropathies. Also, currently, no validated assay for measurement of TNF-α in cats is available.

OBJECTIVES

The objective of this study was to develop and analytically validate an enzyme-linked immunosorbent assay (ELISA) for the quantification of TNF-α in serum from cats.

METHODS

A sandwich ELISA was developed and analytically validated by assessment of detection limit, linearity, accuracy, precision, and reproducibility. A control range for serum fTNF-α concentration in healthy cats was established. In addition, serum concentrations of fTNF-α in 39 cats with chronic enteropathies were compared with those in 20 healthy cats.

RESULTS

The detection limit of the assay was 38.4 ng/L. Observed-to-expected ratios for serial dilutions of 4 serum samples ranged from 75.1% to 111.9%. Observed-to-expected ratios for spiking recovery for 4 serum samples ranged from 91.3% to 129.7%. Coefficients of variation for intra- and inter-assay variability ranged from 3.9% to 7.6% and from 7.8% to 12.5%, respectively. The control range of the assay was < 38.4-223.5 ng/L. Serum concentrations of feline TNF-α were significantly higher in cats with chronic enteropathies and diarrhea than in cats with chronic enteropathies without diarrhea, or in healthy control cats.

CONCLUSIONS

The ELISA described here was suitable for the quantification of fTNF-α in feline serum and should facilitate research into the importance of TNF-α in cats with chronic enteropathies.

Expression of synthetic human tumor necrosis factor is toxic to Escherichia coli

The overlap forward-primer-walk polymerase chain reaction method was used to synthesize the human tumor necrosis factor α (hTNF) gene in Escherichia coli cells. Growth curves for hTNF and pET23d vector cultures exhibited slower doubling rates than cultures containing the pET23d vector alone. Cell cultures transformed with hTNF reached peak densities (0.4-0.6 OD(600)) 3 to 4 h post-induction, then decreased prior to growth recovery. This inhibition occurred in the BL21DE3 strain of E. coli, whereas no inhibition of growth and no expression of hTNF were observed in the JM109 strain of E. coli containing hTNF. Induced hTNF cultures hyperexpressed the hTNF-histidine fusion protein for the first 3 to 4h of induction; subsequently, growth retardation was observed. Hyperexpression and continuous growth were observed in the extracellular expression system. Electron microscopy revealed that accumulation of hTNF inclusion bodies was apparent only in the intracellular expression system - no accumulation was observed with regard to the secretory system. The hTNF-pET23d vector was purified from cells expressing the fusion protein and from cells with recovered growth curves. Sequencing of the vector demonstrated the complete hTNF gene and T7 promoter in cells expressing the fusion protein and mutations of the T7 promoter site from recovered cells.

Vaccination with vif-deleted feline immunodeficiency virus provirus, GM-CSF, and TNF-alpha plasmids preserves global CD4 T lymphocyte function after challenge with FIV

Feline immunodeficiency virus (FIV) DNA vaccine approaches that included a vif-deleted FIV provirus (FIV-pPPRDeltavif) and feline cytokine expression plasmids were tested for immunogenicity and efficacy by immunization of specific pathogen free cats. Vaccine protocols included FIV-pPPRDeltavif plasmid alone; a combination of FIV-pPPRDeltavif DNA and feline granulocyte macrophage-colony stimulating factor (GM-CSF) and tumor necrosis factor (TNF)-alpha expression plasmids; or a combination of FIV-pPPRDeltavif and feline interleukin (IL)-15 plasmids. Cats immunized with FIV-pPPRDeltavif, GM-CSF and TNF-alpha plasmids demonstrated an increased frequency of FIV-specific T cell proliferation responses compared to other vaccine groups. Immunization with FIV-pPPRDeltavif and IL-15 plasmids was distinguished from other vaccine protocols by the induction of antiviral antibodies. Suppression of virus loads was not observed for any of the FIV-pPPRDeltavif DNA vaccine protocols after challenge with the FIV-PPR isolate. However, prior immunization with FIV-pPPRDeltavif, GM-CSF, and TNF-alpha plasmids resulted in preservation of CD4 T cell functions, including mitogen-induced cytokine expression and antigen-specific proliferation upon infection with FIV. These findings justify further examination of cytokine combinations as adjuvants for lentiviral DNA vaccines.

Gene-expression changes induced by Feline immunodeficiency virus infection differ in epithelial cells and lymphocytes

Infection of cats with Feline immunodeficiency virus (FIV) is an important model for understanding comparative lentivirus biology. In vivo, FIV infects lymphocytes and monocyte/macrophages, but in vitro infection is commonly investigated in epithelial Crandell-Reese Feline Kidney (CRFK) cells. In this study, the transcriptional responses of CRFK cells and primary lymphocytes to infection with FIV 34TF, a cloned subtype A virus, and FIV USgaB01, a biological subtype B isolate, were determined. Reverse-transcribed mRNA from both cell types was hybridized to microarrays containing 1700 human expressed sequence tags in duplicate and data were analysed with Significance Analysis of Microarrays (sam) software. Results from six experiments assessing homeostatic cross-species hybridization excluded 3.48 % inconsistently detected transcripts. Analysis of data from five time points over 48 h after infection identified 132 and 24 differentially expressed genes in epithelial cells and lymphocytes, respectively. Genes involved in protein synthesis, the cell cycle, structure and metabolism were affected. The magnitude of gene-expression changes ranged from 0.62 to 1.62 and early gene induction was followed by downregulation after 4 h. Transcriptional changes in CRFK cells were distinct from those in lymphocytes, except for heat-shock cognate protein 71, which was induced at multiple time points in both cell types. These findings indicate that FIV infection induces transcriptional changes of a modest magnitude in a wide range of genes, which is probably reflective of the relatively non-cytopathic nature of virus infection.

Molecular cloning of feline tumour necrosis factor receptor type I (TNFR I) and expression of TNFR I and TNFR II in lymphoid cells in cats

Tumour necrosis factor (TNF)-alpha is a pro-inflammatory cytokine produced by many types of cells. It has been shown that two distinct TNF receptors (TNFRs), TNFR type I (TNFR I) and TNFR type II (TNFR II), have different functions in signal transduction, which is possibly associated with the development of a variety of diseases. In this study, we isolated a feline TNFR I cDNA clone and analysed the expression of TNFR I and TNFR II mRNA in feline lymphoid cells. The deduced amino acid sequence of feline TNFRI cDNA showed 75.8, 62.5 60.9 and 72.1% similarity with those of its human, mouse, rat, and pig counterparts, respectively. The feline TNFR I cDNA was shown to encode extracellular, transmembrane and intracellular domains fundamentally conserved in the homologues of other species. Expression of TNFR I and TNFR II mRNAs was shown to be up-regulated in feline peripheral blood mononuclear cells (PBMC) by stimulation with concanavalin A. Five of six feline lymphoma cell lines were shown to express both TNFR I and TNFR II mRNAs. The expression of TNFR I in PBMC was up-regulated in cats infected with feline immunodeficiency virus (FIV), whereas the expression of TNFR II in PBMC was not different between FIV-infected cats and uninfected cats. The present study indicate that expression of TNFR I and TNFR II may be associated with disease progression, especially in retrovirus infections in cats.

Effects of mastectomy on composition of peripheral blood mononuclear cell populations in periparturient dairy cows

There is an increased incidence of infectious disease in periparturient dairy cows. During the periparturient period there is a decline in T-lymphocyte cell subsets, which parallels a reduction in functional capacities of blood lymphocytes and neutrophils. Mechanisms responsible for these changes in immune function during the periparturient period are poorly characterized. Ten mastectomized and eight intact multiparous Jersey cows were used to determine whether the periparturient changes in peripheral blood mononuclear cell populations are the result of the physiological demands associated with the onset of lactation or whether they are a result of the act of parturition. Blood mononuclear cells were phenotyped with monoclonal antibodies against T-cell subsets, B-cells, and monocytes. Blood samples were taken frequently from before 4 to 4 wk after parturition. In intact cows, all T-cell subset populations (i.e., CD3-, CD4-, CD8-, and gamma-delta positive cells) decreased at the time of parturition, while the percentage of monocytes increased. Mastectomy eliminated the changes in leukocyte subset populations (CD3-, CD4-, and gamma-delta positive cells, and monocytes) observed in intact cows around parturition. These results indicate that the mammary gland and metabolic stresses associated with lactation influence the composition of peripheral blood mononuclear cell populations in dairy cows during the periparturient period.

Bioactivities of a tumour necrosis-like factor released by chicken macrophages

To test for tumour necrosis-like factor (TNF) of chickens, supernatants of a lipopolysaccharide (LPS)-stimulated chicken macrophage cell line MQ-NCSU were analysed. A sequence of ion-exchange and gel-permeation chromatography was utilised to isolate TNF-like activity from the culture supernatant. The peak of TNF-like cytotoxic activity corresponded to the fractions with a molecular weight of 81 kDa or higher. Polyclonal anti-human TNF-alpha antiserum cross-reacted by Western blotting with a 17 kDa protein in the TNF-containing fraction under denaturing conditions. This result indicated that chicken TNF-like factor in the biologically active form may be a protein multimer of monomers of about 17 kDa. The molecular weight of these monomers is similar to the molecular weight of mammalian TNF-alpha. Chicken TNF-like factor stimulated macrophages by inducing morphological changes, enhancing Ia-expression, nitric oxide (NO) production and by synergising with interferon (IFN)-gamma in the induction of NO release from macrophages. The biological activities were not neutralised by anti-human TNF antiserum. These data suggest that LPS-stimulated chicken macrophages produced a functional homologue to mammalian TNF-alpha. This may be structurally quite different from the mammalian TNF molecule. Other factors may have been co-purified with the chicken TNF-like factor having overlapping functions and molecular weight. However, co-purification of chemokines and interleukin-1, major macrophage derived factors, with the chicken TNF-like factor can be excluded based on the purification strategies.

The role of polymerase chain reaction and its newer developments in feline medicine

We give a brief overview on the principles of the polymerase chain reaction (PCR), reverse transcriptase PCR (RT-PCR), quantitative competitive PCR and real-time PCR (TaqMan technology). The literature dealing with PCR and its role in the diagnosis, pathogenesis and research of infectious diseases of the domestic cat is reviewed. Cross-contaminations which occasionally occur during handling of amplified DNA may be an important problem in the PCR laboratory. In many infectious diseases, PCR results are difficult to interpret as their predictive positive and negative values are not always known. Newer assays, such as TaqMan procedures, are becoming increasingly reliable and cost-effective. It can be expected that additional knowledge on how to interpret PCR results will soon be available.

Compartmentalization of Th1/Th2 cytokine responses to experimental Yersinia pseudotuberculosis infection in cats

Specific pathogen-free cats were inoculated subcutaneously into the drainage areas of the left auricular and popliteal lymph nodes with living Yersinia pseudotuberculosis. Inflammation was evident at the inoculation sites and the regional lymph nodes were palpably enlarged at 48 h post-infection. Lymph node enlargement was due to marked paracortical lymphoid hyperplasia and variable neutrophil infiltrates. Yersinia was cultured from the regional lymph nodes and/or spleens of three of the six cats, indicating systemic spread of bacteria. Specific T-helper 1 and 2 (Th1, Th2) cell-associated cytokine mRNA levels were compared in regional lymph nodes, peripheral blood mononuclear cells (PBMC) and spleen at 48 h post-inoculation. Relative to unstimulated control tissues, there was a significant increase in TNF-alpha, IFN-gamma, IL-12, and IL-10 mRNAs in spleen with down-regulation of IL-4. Significant up-regulation of TNF-alpha and down-regulation of IL-4 were also observed in PBMC. Paradoxically, 48 h stimulated lymph nodes showed only minimal differences in cytokine mRNA expression when compared to lymph nodes from mock-inoculated control animals or unchallenged contralateral lymph nodes from the same animal. This study demonstrated that cats, like mice, respond to an intracellular pathogen such as Y pseudotuberculosis with a predominantly Th1-type immune response. The cytokine responses in regional lymph nodes and spleen were asynchronous, while cytokine stimulation in cells of the spleen was mirrored by PBMC.

Cytotoxicity induced by recombinant human tumor necrosis factor-alpha dependent on the types of its receptors on canine cells

Based on the recent findings that show how recombinant human tumor necrosis factor (rh-TNF)-alpha has potent antitumor activity on human cancer patients when it locally administrated, we have tested the cytotoxicity of rh-TNF-alpha on 3 canine cultured cells: (1) canine kidney carcinoma (CKCa-1), (2) mastocytoma and (3) Mardin Darby canine kidney cells (MDCK). The cell surface expression of TNF-alpha receptors on these canine cells was also determined with anti-human TNF RI and RII polyclonal antibodies. Our data shows that on CKCa-1 which has TNF RI receptors rh-TNF-alpha induced cytotoxicity. By contrast, it exhibited no toxicity on canine mastocytoma which has mainly RII receptors. The data also suggest actinomycin D (ACT-D), an anticancer antibiotic, enhanced the cytotoxicity of rh-TNF-alpha. Combined with ACT-D, rh-TNF-alpha showed the cytotoxicity on MDCK which possessed both TNF RI and RII receptors. The results indicate that the cytotoxicity of rh-TNF-alpha depends on the presence of TNF RI receptors on canine tumor cells.

Listeria monocytogenes and Serratia marcescens infections as models for Th1/Th2 immunity in laboratory cats

Five species of bacteria known to be naturally-occurring pathogens of cats were screened for their ability to grow in feline macrophages in vitro, and to induce antibodies and delayed type hypersensitivity (DTH) responses in vivo. Two of these organisms, L. monocytogenes and S. marcescens, were selected for further study based on clear-cut differences in their in vitro and in vivo behavior. Listeria was macrophage tropic, induced DTH, and evoked poor antibody responses post-recovery, whereas Serratia remained extracellular, did not induce a DTH reaction, and produced high titer of antibodies. Young specific pathogen free cats were then inoculated subcutaneously into the drainage areas of the right and left popliteal and auricular lymph nodes with either L. monocytogenes or S. marcescens. Each of the four lymph nodes were then removed in sequence over a two week period, weighed, cultured for viable bacteria, and RNA extracted for Th1/Th2 cytokine mRNA quantitation. Antibody responses and delayed type hypersensitivity responses were also measured. Identical to pilot studies, cats infected with Serratia developed very high levels of antibody compared to Listeria infected cats but no DTH, while Listeria infected cats produced negligible or low titers of antibodies and strong DTH. Immunity to Listeria occurred around 168 h post infection as evidenced by the disappearance of living bacteria from the nodes, while immunity to Serratia took over 264 h. Pronounced lymph node hyperplasia occurred in both infections, but persisted longer for Serratia. Enlargement of Serratia infected nodes was associated with marked follicular, primary and secondary germinal center and medullary hyperplasia. Germinal center formation in Listeria stimulated nodes was much less intense and dense accumulations of macrophages dissected between follicles downward from the subcapsular sinuses. Although functional and histologic studies showed a clear-cut cell-mediated vs. humoral response in the respective Listeria and Serratia infections, preferential cytokine mRNA upregulation was observed for only two of the five major Th1/Th2 cytokines measured. Interferon-gamma, a Th1 cytokine, was much more elevated in the Listeria stimulated nodes, but TNF-alpha (also a Th1 cytokine) was more elevated in Serratia infected nodes. Interleukin-12, an important Th1 cytokine, was elevated to equal levels in both infections as were the Th2 cytokines IL-4 and IL-10.

Measurement of feline cytokine gene expression by quantitative-competitive RT-PCR

We have developed a method to quantitate feline cytokine gene expression using competitive RT-PCR. Feline cytokine specific primers were developed that encompass an intron, thus allowing differentiation of cDNA vs. genomic DNA amplification products. The PCR products of the primers were verified by sequencing and Southern blot analysis. For quantitation, a non-homologous RNA competitor was created for each cytokine of interest. The competitor was designed to yield an RT-PCR product 10-20% larger than the native sequence, thereby allowing differentiation of the two products by electrophoresis on an agarose gel. Both competitor and native sequences used the same primer sequences for RT (oligo dT) and PCR (cytokine specific). The amplification efficiency of the competitor and native sequence was shown to be identical which allowed comparison at any point during the amplification, including the plateau phase. The quantity of starting cytokine mRNA was determined by interpolation from a standard curve. As little as 1 microgram of total cellular RNA was required per cytokine determination. The assay can routinely quantify as few as 1000 copies of template and spans a range of up to 4 log.

Biological response modifiers: interferons, interleukins, recombinant products, liposomal products

The concept of enhancing the normal immune response against infections and neoplasms has been considered for decades. The administration of various natural and synthetic products to simulate systemic infections has largely given over to the idea that specific cytokines can be used effectively when administered systemically. Interferons, interleukins, and hematopoietic growth factors may offer substantial clinical benefit in chronic viral infections, and cancers such as osteosarcoma, melanoma, and lymphosarcoma. Erythropoietin has been shown to have great utility in the management of chronic renal failure. At this point in time, only recombinant products derived from humans are commercially available, and they are expensive and not licensed for use in companion animals. Nevertheless, these products may have significant clinical impact on several highly fatal disorders of dogs and cats. When administered systemically, cytokines perturb complex regulatory pathways, and serious side effects may occur. Innovative delivery methods, such as liposomes, gene therapy, and even oral administration may increase the therapeutic index of these molecules. Biological response modification, cytokine biology, and associated delivery systems are rapidly changing fields, and the small animal veterinarian will need to watch for significant advances in these areas over the next several years.

Production of polyclonal antibodies to feline tumor necrosis factor

Two 13-amino-acid peptides were synthesized based on the putative feline tumor necrosis factor (FeTNF) sequence. The synthesized peptides were conjugated to keyhole limpet hemocyanin, emulsified in complete Freund's adjuvant, and injected into rabbits. The gene for FeTNF was cloned into the FLAG (International Biotechnologies Inc. [IBI], Kodak, New Haven, Conn.) fusion protein expression vector. The expressed fusion protein was purified by using the M-1 anti-FLAG octapeptide monoclonal antibody (IBI, Kodak). The fusion protein was emulsified in complete Freund's adjuvant and injected into chickens. The immune sera generated to the synthetic peptides and the fusion protein recognized the recombinant FeTNF fusion protein on Western or dot blot assay. The preimmune and immune sera were incubated with naturally occurring FeTNF (supernatants from lipopolysaccharide-stimulated cultured feline peritoneal exudate or peripheral mononuclear cells). The antibody raised to the recombinant FeTNF fusion protein and N-terminal synthetic peptide neutralized bioactivity of native FeTNF and recombinant human TNF. Preimmune sera did not have any neutralizing activity. The polyclonal antibodies were not specific for FeTNF, since both porcine and human recombinant TNF were neutralized by the fusion protein antibodies. The synthetic peptide antibodies recognized recombinant feline and equine TNF on a Western blot.

Apoptosis and T-cell depletion during feline infectious peritonitis

Cats that have succumbed to feline infectious peritonitis, an immune-mediated disease caused by variants of feline coronaviruses, show apoptosis and T-cell depletion in their lymphoid organs. The ascitic fluid that develops in the course of the condition causes apoptosis in vitro but only in activated T cells. Since feline infectious peritonitis virus does not infect T cells, and viral proteins did not inhibit T-cell proliferation, we postulate that soluble mediators released during the infection cause apoptosis and T-cell depletion.

Expression of recombinant feline tumor necrosis factor is toxic to Escherichia coli

The tumor necrosis factor (TNF) genes from cats, horses, and pigs have all been cloned into the pFLAG-1 fusion protein expression vector (International Biotechnologies, Inc., Kodak, New Haven, Conn.). Growth curves for Escherichia coli containing the pFLAG-1 vector alone and the pFLAG-1 vector containing the TNF gene from each species were determined by visible light spectrophotometry (at 600 nm). Porcine TNF, equine TNF, and feline TNF cultures had slower doubling rates than cultures containing the pFLAG-1 vector alone. Cultures of cells transformed with feline TNF reached peak densities at 3 to 4 h and then decreased to near initial densities prior to the recovery of growth. The induction of expression with isopropyl-beta-D-thiogalactopyranoside (IPTG) arrested the growth of fresh feline TNF cultures for 6 h, which was followed by complete recovery. This inhibition occurred in two strains of E. coli (LL308 and JM101). Induced feline TNF cultures expressed the TNF-FLAG fusion protein for the first 6.5 h. Uninduced cultures expressed low levels of fusion protein. The feline TNF-pFLAG-1 vector was purified from cells expressing fusion protein and from cells with recovered growth curves. Sequencing the vector demonstrated the complete feline TNF gene and tac promoter in cells expressing the fusion protein and a deletional mutation of the tac promoter site in recovered cells. In contrast to equine and porcine TNF, the expression of recombinant feline TNF is toxic to E. coli. Alterations in protein folding and the prevention of secretion of the feline protein may explain the toxic effect.