FeLV-infected Cats Research Articles

Feline leukemia virus detection in corneal tissues of cats by polymerase chain reaction and immunohistochemistry.

To determine the presence of feline leukemia virus (FeLV) in the corneas of FeLV-infected cats. Thirty-four random source cats. Seventeen cats were found positive for FeLV serum p27 antigen by enzyme-linked immunosorbent assay (ELISA). Twelve ELISA positive cats were also positive on peripheral blood samples by immunofluorescent antibody (IFA) testing. Seventeen ELISA negative cats served as negative controls. Full thickness corneal specimens were collected from the left cornea of all cats and analyzed for FeLV proviral DNA and gp70 antigen by polymerase chain reaction (PCR) and immunohistochemical (IHC) testing, respectively. Eleven (64.7%) positive corneal PCR results were obtained from 17 ELISA positive cats. Of 12 cats that were both ELISA and IFA positive on peripheral blood, 10 (83.3%) had positive corneal PCR results. All corneal tissues from ELISA negative cats were PCR negative. IHC staining of corneal sections revealed the presence of FeLV gp70 in corneal tissues of nine (52.9%) ELISA positive cats. Of the 12 cats that were both ELISA and IFA positive on peripheral blood, eight (66.7%) had positive corneal IHC results. Positive IHC staining was localized to the corneal epithelium. Corneal tissues of all ELISA negative cats and all IFA negative cats were negative on IHC testing. FeLV antigens and proviral DNA are present in corneal tissues of some FeLV-infected cats. Screening corneal donors for FeLV infection is warranted.

Treatment of feline leukemia virus (FeLV) infection

FeLV infection is still considered to account for most disease-related deaths in pet cats. Different treatment attempts with various drugs were performed in the past but none resulted in healing or complete virus elimination. Therefore, it caused a sensation when Hörber and Mayr [Hörber, D., Mayr, B., 1991. Prax. 19, 311–314; Hörber, D., Schnabl, W., Mayr, B., 1992. Tierärztl. Umschau 47, 556–560; Mayr, B., Hörber, D., 1992. Kleintierprax. 37, 515–518] published that they were able to cure 80 to 100% FeLV-infected cats from viremia by using an immunomodulating compound. Articles in cat breeder and cat owner journals appeared assuming that obviously there is a rescue for FeLV-infected cats suffering from this deadly infection. The immunomodulator [ Büttner, M., 1993. Comp. Immun. Microbiol. Infect. Dis. 18, 1–10] used in those studies was the so-called ‘paramunity inducer’ PIND-ORF (Baypamun ®, Bayer, Leverkusen, Germany) consisting of inactivated parapox ovis virus. Since that time, Baypamun ® is the most commonly used drug for treatment of FeLV infection in Germany and other European countries. Four placebo-controlled double-blind trials were performed to determine the therapeutic efficacy of Baypamun ® and other compounds in naturally FeLV-infected cats under controlled conditions.

Evaluation of in vivo and in vitro interactions of feline immunodeficiency virus and feline leukemia virus.

To determine the potential mechanisms for disease potentiation where feline immunodeficiency virus (FIV) infection of persistently feline leukemia virus (FeLV)-infected cats results in more severe FIV disease and increased mortality than FIV infection of specific pathogen-free cats. To determine whether pseudotype formation resulting in expanded cell tropism may be an important mechanism, cellular targets and tissue distribution of FIV and FeLV were determined by in situ hybridization and/or immunohistochemistry. To determine whether FeLV can transactivate the FIV long terminal repeat (LTR) resulting in increased FIV expression, in vitro transient expression assays were performed. To examine whether persistent FeLV infection can cause the deletion of a suppressive T-lymphocyte population, peripheral blood mononuclear cell (PBMC) cultures from persistently FeLV-infected cats were infected with FIV and monitored for FIV antigen levels. Macrophages were the predominant target of FIV infection and were disseminated in a similar pattern in lymphoid and nonlymphoid tissues of both FIV-infected and FeLV/FIV-coinfected cats. FeLV-infected cells expressing FIV RNA were not present. Significant transactivation of the FIV LTR in FeLV-infected cells was not demonstrated. FIV antigen production was similar upon in vitro infection of PBMC from FeLV-infected and uninfected cats. Neither direct virus/virus interactions, such as FeLV/FIV pseudotype formation or transactivation of the FIV LTR in FeLV-infected cells, nor deletion of a regulatory cell subset from the blood of FeLV-infected cats, was found to be the mechanism of disease potentiation.

Induction of Feline Acquired Immune Deficiency Syndrome by Feline Leukemia Virus: Immuno- and Neuroendocrine Dysfunctions

Young cats, when chronically infected with feline leukemia virus (FeLV), developed feline acquired immune deficiency syndrome (FAIDS). The syndrome was associated with a sequence of dysfunctions in the hypothalamic-pituitary-gonadal (HPG) and the immune system, manifested in the reduction of luteinizing hormone-releasing hormone (LHRH), follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone in blood plasma. The average FSH and LH (in plasma or lymphocyte), testosterone, and LHRH concentrations in the 20 FeLV-infected cats were measured by radioimmunoassay. The results were compared with those of the 12 control cats that were not FeLV-infected. Four weeks after infection, the plasma LHRH concentration in the infected cats showed a 43% reduction. Five to six weeks after infection, the content of FSH and LH in lymphocyte was reduced by 50% and 28%, respectively, whereas, the plasma FSH and LH was reduced by 52% and 42%, respectively. A significant reduction in testosterone content was detected at Week 11 of infection. The onset of the immuno- and neuroendocrine dysfunctions in FAIDs cats followed this sequence: hypothalamus, lymphocyte, pituitary, adrenal gland, and gonads. Indirect immunofluorescence assay showed the presence of FeLV cytoplasmic antigens in the fibers of the hypothalamic preoptic region and the Leydig cells. The possible causal relationship between the dysfunction of the lymphocyte and HPG systems and the presence of FeLV was discussed.

Serum HIV-1 p24 levels and body weight measurements before and after 4 weeks of diethylcarbamazine treatment given to HIV-1 seropositive persons

Previous reports suggest that diethylcarbamazine citrate (DEC) could be useful in the treatment of retroviral, bacterial, and fungal infections [1]. In an additional experiment, DEC (25 mg by mouth twice daily) was administered concurrently with oral Zidovudine (20 mg/kg twice daily, later changed to 10 mg/kg, then 15 mg/kg oral Videx twice daily) to a chronically FeLV-infected 18-month-old female domestic shorthair cat (cat S). FeLV serum p27 levels were lowered (by a factor of 10) with no apparent adverse effects or notable changes in serum alanine aminotransferase and creatinine levels, and a weight gain of 0.5 kg was noted over 4 months. Another study indicated that 1 month of oral DEC (10 mg/kg day -~) given to 12 FeLV-infected cats did not significantly alter serum alanine aminotransferase and

Chronic feline leukemia virus infection alters arachidonic acid proportions in vivo and in vitro.

The polyunsaturated omega-6 fatty acid, arachidonic acid ([AA] 20:4n-6), is both the key of the immunoregulatory substances, prostaglandins, and leukotrienes, and an essential component of immune cell membrane phospholipids, providing stability and flexibility to ensure cellular function. To explore possible effects of the physiological burden of viral replication in chronic viral infections on AA availability, plasma total esterified fatty acid (FA) proportions were measured in the feline leukemia (FeLV) model. Plasma FA profiles of 12 specific-pathogen-free cats with chronic infections with Rickard strain feline leukemia virus (FeLV-R) were compared with 12 age- and sex-matched uninfected specific-pathogen-free cats at 4 months after infection. A significant decrease from normal of average AA proportion was found in FeLV-R-infected cat plasma, while other major FA (palmitic, stearic, and oleic and omega-3 FA normally remained present until near death. Since plasma FA content rapidly affects circulating immune cell membrane composition and since FeLV infection also targets immune cells, we compared FA profiles of feline T4-thymic lymphoma 3201 cell membranes that were infected with virulent FeLV-R or less virulent FeLV-A, at 20 days after viral inoculation with sham-inoculated uninfected 3201 cells. Significantly altered FA proportions and ratios of saturated to unsaturated FA found in infected cell membranes were similar to plasma FA changes and paralleled the virulence of the FeLV inoculum. Altered postinfection FA proportions may impart serious functional defects to the immune cells of chronic FeLV-infected cats, contributing to the inability of their immune systems to eliminate FeLV by depleted plasma AA stores and modified cell membrane composition. Decreased AA availability may be an important factor in the cachexia and fatal outcome of FeLV infection.

Detection of enhancer repeats in the long terminal repeats of feline leukemia viruses from cats with spontaneous neoplastic and nonneoplastic diseases

Enhancer duplication in the long terminal repeat of feline leukemia virus (FeLV) was examined in primary cells from naturally FeLV-infected cats with various neoplastic and nonneoplastic diseases using the polymerase chain reaction. In all cases, a 170-bp band, corresponding to a standard exogenous FeLV with one copy of enhancer, was detected. Repeated enhancer sequences were found in all 8 cases of thymic-form lymphosarcoma, in some cases of lymphosarcoma of other forms ( 3 8 ) and myeloid tumors ( 2 3 ), and in only 1 of 6 cases with nonneoplastic diseases. The copy number of FeLV proviruses with a repeated enhancer seemed higher than that of those with one copy of enhancer in 3 cases of thymic form lymphosarcoma. In 5 cases of thymic form lymphosarcoma and in 1 case of erythroleukemia, coexistent FeLVs with double and triple enhancers of different sizes were found. Of the enhancer elements, only the SV40 core binding site was found in all the enhancer direct repeats of these FeLVs. All the provirus clones with single and duplicated enhancer sequences from a single tumor showed mutations or deletions characteristic to that tumor, indicating that enhancer repeats may arise in individual animals after infection with a single virus clone. The present findings indicate that FeLV with enhancer repeats generated in the cat is associated with the induction of neoplastic diseases in natural conditions.

Evaluation of feline immunodeficiency virus and feline leukemia virus transmembrane peptides for serological diagnosis.

The general model for retrovirus transmembrane (TM) proteins proposed by Gallaher et al. (W. R. Gallaher, J. M. Ball, R. F. Garry, M. C. Griffin, and R. C. Montelaro, AIDS Res. Hum. Retroviruses 5:431-440, 1989) suggests that all retrovirus TM proteins may contain an immunodominant domain (Imd-TM peptide) located at the apex of the TM polypeptide. Although this Imd-TM peptide has been shown to be immunodominant in a variety of lentivirus infections, there has not been a detailed serological analysis of an oncovirus Imd-TM peptide as a diagnostic agent. We describe here an analysis of the antigenic properties and diagnostic potentials of the predicted Imd-TM peptides of feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) in serological assays of sera from infected cats. The results of these studies demonstrate that antibodies specific to the FIV Imd-TM peptide are detected within 2 weeks postinfection, are maintained at high levels for extended periods, and are not detectable in uninfected or FeLV-infected cats. In marked contrast, the FeLV Imd-TM peptide displayed only negligible levels of serological reactivity in FeLV-infected cats. These studies indicate that the peptide is a useful reagent for the detection of antibodies to FIV.

Tumour necrosis factor-? levels and the effects of pentoxifylline in cats with feline leukaemia virus infection

Tumour necrosis factor-α (TNF-α) levels were measured in supernatants of macrophage cultures infected in vitro with feline leukaemia virus (FeLV) and in serum, bone marrow plasma, and supernatants of bone marrow mononuclear cell (BMMC) cultures from cats infected with an anemogenic strain of FeLV. TNF-α levels significantly increased (p < 0.05) in the supernatants of in vitro FeLV-infected macrophage cultures compared with uninfected cultures. TNF-α levels in serum and culture supernatants of BMMC from FeLV-infected cats were also significantly increased (p < 0.05) compared with baseline values. Pentoxifylline is a dimethylxanthine derivative that inhibits TNF-α production. Pentoxifylline treatment of FeLV-infected macrophage cultures caused a significant decrease in TNF-α levels. Pentoxifylline given orally to FeLV-infected cats from week 0 to week 5 post-inoculation did not cause significant inhibition of TNF-α levels. Although a trend toward higher numbers of erythroid and fibroblast progenitors was observed in pentoxifylline-treated cats, the changes were not significantly different. The persistent increase in TNF-α levels in serum and culture supernatants of BMMC from FeLV-infected cats suggests that TNF-α may be important in the pathogenesis of hematopoietic suppression.

Early events in the immunopathogenesis of feline retrovirus infections

Summary Feline leukemia virus and feline immunodeficiency virus (fiv) are lymphotropic retroviruses that cause a wide range of diseases in domestic cats. Although it is known that both viruses are capable of infecting T lymphocytes and that infected cats are lymphopenic, it was not known how infection with either virus might alter specific lymphocyte subpopulations. Using a panel of monoclonal antibodies to feline lymphocyte subpopulations, we examined, by use of flow cytometric analysis, lymphocyte changes in cats naturally infected with FeLV or fiv and explored the early stages in the immunopathogenesis of experimentally induced infection with these viruses. Both groups of naturally infected cats had T-cell lymphopenia. In the fiv-infected cats, the T-cell decrease was principally attributable to loss of CD4+ cells, whereas CD8+ and B-cell numbers remained normal. This led to inversion of the CD4+ to CD8+ ratio in these cats. In contrast, the T-cell lymphopenia in FeLV-infected cats resulted from decrease in CD4+ and CD8+ cells, which led to a CD4+ to CD8+ ratio within normal limits. Experimentally induced infection with these 2 viruses supported these findings. Infection with FIV induced early (10 weeks after infection), chronic inversion of the CD4+ to CD8+ ratio. In contrast, infection with FeLV did not alter CD4+ to CD8+ ratio in the first 20 weeks after infection.

Year two of follow-up evaluation of a randomized, blind field trial of a commercial feline leukemia virus vaccine

Summary A blind randomized field trial of a commercial FeLV vaccine was conducted. Cats on study were vaccinated with either a commercial FeLV vaccine or a placebo, then housed with FeLV-positive cats in a ratio of approximately 2 study cats to 1 infected cat (results of the first 12 months of the study have been reported). All surviving placebo-treated and FeLV-vaccinated cats were re-vaccinated 1 year after initial exposure to FeLV-infected cats. Exposure continued for an additional 12 months, and the viremia status of the cats was monitored by immunofluorescent antibody (ifa) and elisa testing at 4-month intervals. During the second year of observation, 1 additional FeLV-vaccinated cat had positive results of 2 consecutive elisa tests, but remained ifa negative. Classifying this cat as persistently viremic reduced the estimate of the preventable fraction, but did not alter the conclusions drawn earlier, viz, that vaccination appreciably reduces the number of cats that become persistently viremic after long-term natural exposure.

Inhibition of phorbol ester-induced neutrophil chemiluminescence by FeLV

Receptor-mediated activation is accompanied by phospholipid metabolism and by calcium fluctuation resulting in a chemiluminescence (CL) response in the neutrophil. This pathway involves activation of protein kinase C (PKC) and the NADPH oxidase. Artificial stimulants such as phorbol esters, specifically 12-O-tetradecanylphorbol-13-acetate (TPA), circumvent the receptor-mediated pathway and activate PKC resulting in a measurable CL response. Neutrophils from feline leukemia virus (FeLV) exposed cats were tested for their ability to generate a TPA-induced CL response. As compared to the non-FeLV-exposed specific-pathogen-free (SPF) control cat neutrophil CL responses, both viremic and nonviremic FeLV-exposed cats showed significant decreases in their CL responsiveness. Neither ultraviolet light-inactivated FeLV (UV-FeLV) nor protein components (FeLV-p15E and FeLV-p27) caused a significant decrease in the CL responses of the SPF cat neutrophils. The suppressed TPA-induced CL response from FeLV-infected cats may involve an intracellular mechanism not affected in vitro by exposure of the neutrophil to the virus or viral components.

Hematologic effects of short-term oral diethylcarbamazine treatment given to chronically feline leukemia virus-infected cats

Diethylcarbamazine (N,N-diethyl-4-methyl-1-piperazine carboxamide [DEC]) is widely used, especially in tropical regions, to prevent and treat filariasis. The antifilarial effect of this drug has been attributed to immunomodulation. Evidence is accumulating to indicate that DEC may mitigate the course of feline leukemia virus infection (FeLV) in cats. Previous studies have suggested that continuous oral DEC treatment given shortly after evidence of FeLV infection prevents or delays lymphopenia and prolongs survival. The present study focuses on the hematologic effects of one month oral DEC treatment given to adult chronically FeLV-infected cats and uninfected cats as compared to untreated FeLV-infected cats. Such treatment frequently resulted in abruptly lowered peripheral lymphocyte counts in chronically FeLV-infected cats. Further studies are warranted to evaluate whether administration of DEC could eliminate circulating retroviral-infected cells.

Testing of Nucleoside Analogues in Cats Infected with Feline Leukemia Virus: A Model

In the present communication we evaluate the feline leukemia virus (FeLV) infection of cats as a model for antiretroviral chemotherapy studies. Additionally, we report the results of testing the antiviral effect of the compounds, 3'-azido-3'-deoxythymidine (AZT), 2',3'-dideoxycytidine, 2',3'-dideoxyinosine and 2',3'-dideoxyadenosine against FeLV replication in vitro. Cumulative data from experiments in which FeLV-infected cats were treated with AZT at different stages of experimental infection are also evaluated.

Effect of diethylcarbamazine on testing serum samples for retroviral antibodies

Previous investigations have revealed that in vivo use of diethylcarbamazine ( N,N-diethyl-4-methyl-1-piperazine carboxamide; DEC), the mainstay of prevention and therapy for filariases, results in increased titers of antibody to feline oncornavirus-associated cell membrane antigen (FOCMA) in feline leukemia virus (FeLV)-infected cats.In the present study, the effect of in vitro DEC on detection of serum antibodies to retroviruses was investigated. The addition of DEC (5 mg ml −1, pH 7·3–7·4) to the serum diluent resulted in detection of antibody to FOCMA by indirect membrane immunofluorescence in five of five FeLV-infected cats, whereas samples from all five cats tested negative without the addition of DEC. In vitro DEC also increased the absorbance values generated by enzyme immunoassay human immunodeficiency virus type 1 (HIV-1) antibody testing of samples from (a) persons with AIDS-related disease; (b) persons with helper T-lymphocytes < 500 mm −3 blood; and (c) persons testing positive for antibody to HIV-1 env- but not gag-related antigens as determined by radioimmunoprecipitation and sodium dodecyl sulfate polyacrylamide gel electrophoresis ( RIP-SDS PAGE ). We conclude that in vitro as well as in vivo use of DEC may alter results of antibody testing for retroviruses.

Feline Leukemia/Sarcoma Viruses and Immunodeficiency

Publisher SummaryThis chapter discusses the structure feline leukemia virus (FeLV) and pathogenesis of lymphomas and leukemias BY FeLV. FeLV is quite similar to the better-studied murine leukemia viruses in structure and genetic map. The virus particles bud from cytoplasmic membranes into either extracellular spaces or into vacuoles. FeLV has long been considered a typical noncytopathogenic, longlatency leukemia virus based on its behavior in fibroblasts in vitro. Recent evidence suggests that its in vivo behavior in critical target hemolymphatic tissues is as likely to be cytopathic as transforming. The type of FeLV-related disease that occurs and the disease-free interval probably are influenced by viral envelope proteins and glycoproteins and the consequences of proviral integration. FeLV subgroup specificity apparently determines when and what type of disease will occur. The ecotropic FeLV-A is the most frequent subgroup found in pet cats and is transmitted contagiously. Immunosuppression is the most frequent and the most devastating manifestation of FeLV viremia in clinical and experimental studies. It seems that multiple cell types and multiple processes are involved in the development of feline retrovirus-induced immunosuppression. Although no solid evidence is available for the malfunctioning of cat T helper cells because of the paucity of T-cell specific markers, the circumstantial evidence provided thus far indicates an impaired T helper function in FeLV-infected cats similar to that observed in humans infected with HIV. Studies on the pathogenesis of FeLV-induced immunosuppression might provide a valuable mode for a better understanding and means of control of human AIDS.

The decline in the production of interleukin 2 in cats spontaneously infected with feline leukemia virus.

Twelve cats, confirmed to be positive for group specific antigens of feline leukemia virus (FeLV) in peripheral blood lymphocytes (PBL) by an indirect immunofluorescent antibody test, were studied for interleukin 2 (IL-2) production. The production of IL-2, determined by the cell proliferation of an IL-2 dependent murine T cell line (CTLL-2), was remarkably lower in PBL from FeLV-infected cats, as compared to those from healthy controls. In particular, FeLV-infected cats with leukemia or with the thymic type of lymphosarcoma had substantially poor IL-2 production. These results suggest that the proliferative response of PBL from persistently FeLV-infected cats to Con A is reduced, associating with the lowered ability of IL-2 production at least in part.

Viral transduction of host genes in naturally occurring feline T-cell leukaemias: transduction of myc and a T-cell antigen receptor beta-chain gene.

Feline leukaemia virus has been a particularly useful tool in cancer research since many of the naturally occurring tumours associated with this virus group have yielded recombinant retroviruses containing hostderived oncogenic information. The prevalence of transduction as an oncogenic mechanism was seen first in multicentric fibrosarcoma, a relatively rare tumour in FeLV-infected cats (Hardy et al. 1982; Besmer 1984). In a significant percentage of cases of this disease, oncogene-containing feline sarcoma viruses have been identified. More recently, we and others have found that in the more common FeLV-associated neoplasm, thymic lymphosarcoma, viral capture of the c-myc gene can occur (Neil et al. 1984; Levy et al. 1984; Mullins et al. 1984). Since the oncogenes carried by feline sarcoma viruses do not include myc, these reports provided the first evidence that myc may be a target for oncogenic activation by FeLV.KeywordsViral TransductionFeline Leukaemia VirusAntigen Receptor GeneProviral InsertionAntigen Receptor Gene RearrangementThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Humoral immune response of asymptomatic cats naturally infected with feline leukemia virus

The humoral immune response of cats that were naturally infected with the feline leukemia virus (FeLV) was examined after antigenic stimulation with the synthetic antigen poly(L-Tyr, L-Glu)-poly(DL-Ala)-poly(L-Lys). The primary humoral antibody response in FeLV-infected cats was both delayed and greatly reduced, compared with that seen in uninfected control cats. A similar discordance was observed after secondary stimulation with the antigen, in the FeLV-infected cats had both a delayed response and a reduced response, compared with uninfected cats. The levels of total immunoglobulins of the immunoglobulin G and immunoglobulin M classes in the sera of FeLV-infected cats were significantly higher (two- and threefold, respectively) than were those of the uninfected control animals. The presence of an impaired humoral immune response to newly presented antigens in the presence of elevated immunoglobulin levels has been thoroughly documented in the case of people with the acquired immunodeficiency syndrome. This further emphasizes the potential value of FeLV-infected cats as a model for human acquired immunodeficiency syndrome.

Polymorphonuclear leukocyte dysfunction associated with feline leukaemia virus infection.

The chemiluminescent characteristics of enriched (greater than 95%) peripheral blood polymorphonuclear leukocyte populations (PMN) from normal and feline leukaemia virus (FeLV)-infected cats were investigated. FeLV-infected cats demonstrated a significantly lower (P less than 0.001) PMN chemiluminescent response when compared to the response of normal age-matched controls. Normal PMN treated with FeLV-infected cat serum exhibited a depressed response in comparison to control cells. A titration of serum from infected cats supplemented with normal serum revealed a titratable suppression of chemiluminescence with increasing concentration of serum from the infected cats. However, PMN from FeLV-infected cats treated with normal serum displayed a slight increase in chemiluminescence over the same cells in autologous serum. The addition of inactivated FeLV to normal PMN caused a titratable decrease in chemiluminescence.