Tumor necrosis factor alpha levels in cats experimentally infected with feline immunodeficiency virus: effects of immunization and feline leukemia virus infection.

Tumor necrosis factor alpha (TNF alpha) levels were determined by enzyme-linked immunosorbent assay (ELISA) and by cell culture bioassay in supernatants of lipopolysaccharide-stimulated feline monocyte cultures and in cat serum samples. There was a good correlation between the results obtained by the two methods. From the fact that TNF alpha was neutralized quantitatively by antibodies to human TNF alpha in feline monocyte supernatants and in feline sera, it was concluded that feline TNF alpha immunologically cross-reacts with human TNF alpha and that the human TNF alpha ELISA can be used to quantitate feline TNF alpha. During the first 6 months after experimental feline immunodeficiency virus (FIV) infection no differences in serum TNF alpha values were observed between infected and non-infected cats. TNF alpha levels increased significantly after primary vaccination with a feline leukemia virus (FeLV) vaccine in FIV infected cats over those in the non-infected controls. During secondary immune response TNF alpha levels rose transiently for a period of a few days in both the FIV positive and the FIV negative cats. After FeLV challenge, TNF alpha levels increased in all animals challenged with virulent FeLV for a period of 3 weeks. This period corresponded to the time necessary to develop persistent FeLV viremia in the control cats. It was concluded from these experiments that in the asymptomatic phase of FIV infection no increased levels of TNF alpha are present, similar to the situation in asymptomatic HIV infected humans. Activation of monocytes/macrophages in FIV infected cats by stimuli such as vaccination or FeLV challenge readily leads to increased levels of TNF alpha.     

Altered surface antigen expression on peripheral blood mononuclear cells in cats infected with feline immunodeficiency virus.

Expression of CD4, CD8, IL-2 receptor alpha chain (IL-2R alpha), and MHC class II (MHC-II) on peripheral blood mononuclear cells were examined in cats infected with feline immunodeficiency virus (FIV). CD4/CD8 T cell ratio in FIV-infected cats was slightly decreased, as compared with that in specific-pathogen-free (SPF) cats. However, there was no statistical differences between them. The number of circulating IL-2R alpha+ cells in FIV-infected cats was higher than that in healthy cats, whereas induction of IL-2R alpha expression by concanavalin A (Con A) stimulation was depressed in FIV-infected cats. By using two-color cytofluorometry, Con A-induced enhancement of IL-2R alpha expression was found to be reduced in both CD4+ and CD8+ populations in PBMC from FIV-infected cats. The circulating MHC-II+ cells were also increased in FIV-infected cats. Furthermore, the induction of IL-2R alpha expression on PBMC after Con A-stimulation significantly depressed by FIV inoculation in vitro. These results suggest that FIV activates PBMC in vivo via direct and/or indirect mechanisms, leading to the unresponsive state of T cells to further stimuli in vitro.     

Effect of bovine lactoferrin on functions of activated feline peripheral blood mononuclear cells during chronic feline immunodeficiency virus infection

Feline immunodeficiency virus (FIV) infection is characterized by chronic overactivation of immune and inflammatory system, resulting in anergic state and dysfunction of immune cells. Lactoferrin (LF), a glycoprotein present in exocrine secretions and neutrophils, plays an important role in host defense system. Our previous study showed that oral administration of bovine LF (bLF) suppressed oral inflammation, improved the clinical symptoms and decreased serum gamma-globulin as a marker of inflammation in FIV-infected cats with intractable stomatitis. The anti-inflammatory effect was partly involved in regulation of neutrophil function by bLF. In this study, to clarify the relationship between anti-inflammatory effects of bLF and peripheral blood mononuclear cells (PBMC), we examined the effect of bLF on proliferation, cell cycle progression and cytokine expression in mitogen-activated PBMC. MTT [3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyl tetrazolium bromide] assay showed that bLF inhibited the concanavalin A (ConA)-induced cell proliferation in FIV-infected cats with the asymptomatic carrier and AIDS-related complex (ARC) phase. Bovine LF restored ConA-induced cell cycle progression and resulted in suppression of the induced apoptosis in feline PBMC. Real-time RT-PCR showed that bLF suppressed ConA-induced expression of interferon-gamma and interleukin-2 in cells of the ARC group regardless of the time of its addition to the medium. These results suggest the hypothesis that therapy with bLF may have the potential to improve and protect functions of overactivated lymphocytes by modulating the cell proliferation, cell cycle and cytokines expression in cats in terminal stage of FIV infection.     

Prevalence of feline leukemia virus infection and serum antibodies against feline immunodeficiency virus in unowned free-roaming cats

OBJECTIVE: To determine prevalence of FeLV infection and serum antibodies against feline immunodeficiency virus (FIV) in unowned free-roaming cats. DESIGN: Cross-sectional serologic survey. ANIMALS: 733 unowned free-roaming cats in Raleigh, NC, and 1,143 unowned free-roaming cats in Gainesville, Fla. RESULTS: In Raleigh, overall prevalence of FeLV infection was 5.3%, and overall seroprevalence for FIV was 2.3%. In Gainesville, overall prevalence of FeLV infection was 3.7%, and overall seroprevalence for FIV was 4.3%. Overall, FeLV prevalence was 4.3%, and seroprevalence for FIV was 3.5%. Prevalence of FeLV infection was not significantly different between males (4.9%) and females (3.8%), although seroprevalence for FIV was significantly higher in male cats (6.3%) than in female cats (1.5%). CONCLUSIONS AND CLINICAL RELEVANCE: Prevalence of FeLV infection and seroprevalence for FIV in unowned free-roaming cats in Raleigh and Gainesville are similar to prevalence rates reported for owned cats in the United States. Male cats are at increased risk for exposure to FIV, compared with female cats.     

Long-term impact on a closed household of pet cats of natural infection with feline coronavirus, feline leukaemia virus and feline immunodeficiency virus

A closed household of 26 cats in which feline coronavirus (FCoV), feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) were endemic was observed for 10 years. Each cat was seropositive for FCoV on at least one occasion and the infection was maintained by reinfection. After 10 years, three of six surviving cats were still seropositive. Only one cat, which was also infected with FIV, developed feline infectious peritonitis (FIP). Rising anti-FCoV antibody titres did not indicate that the cat would develop FIP. The FeLV infection was self-limiting because all seven of the initially viraemic cats died within five years and the remainder were immune. However, FeLV had the greatest impact on mortality. Nine cats were initially FIV-positive and six more cats became infected during the course of the study, without evidence of having been bitten. The FIV infection did not adversely affect the cats' life expectancy.     

Macrophage functions in cats experimentally infected with feline immunodeficiency virus and Toxoplasma gondii.

It was suspected that feline immunodeficiency virus (FIV) infection would affect the function of feline macrophages, and that the concomitant infection of cats with FIV and Toxoplasma gondii would cause even greater changes in macrophage function. Sixteen specific-pathogen-free kittens, four per group, were infected either with FIV, T. gondii, both pathogens, or neither pathogen. After the cats had been infected with FIV for 14 weeks (8 weeks after T. gondii infection), peritoneal macrophages were collected. Some macrophages were stimulated with lipopolysaccharide and supernatants were collected for the measurement of interleukin-1 production. Other macrophages were infected with T. gondii in a microbiocidal assay. Peritoneal macrophages from cats infected with FIV had decreased interleukin-1 secretion and increased antimicrobial activity. Co-infection with T. gondii apparently had no effect on these modifications of macrophage activity. Thus, acute FIV infection alone caused significant changes in macrophage functions that were not affected by concomitant T. gondii infection.     

Epizootiologic association between feline immunodeficiency virus infection and feline leukemia virus seropositivity

Five hundred twenty-one feline serum samples submitted to the Texas Veterinary Medical Diagnostic Laboratory between Nov 1, 1988, and Jan 31, 1989 were tested for antibody to feline immunodeficiency virus (FIV) by use of an ELISA. The prevalence of FIV infection in this population was 11.3% (95% confidence interval: 8.6 to 14.0%). Serologic test results for FeLV were available for 156 of the 521 cats. A significant (P = 0.008) association between FIV infection and FeLV seropositivity was observed; FeLV-positive cats were nearly 4 times more likely to be seropositive for FIV than were FeLV-negative cats. The association remained statistically significant (P = 0.021) after adjusting for age and gender, using multiple-logistic regression analysis.     

Interaction of acute feline herpesvirus-1 and chronic feline immunodeficiency virus infections in experimentally infected specific pathogen free cats.

Cats with or without chronic feline immunodeficiency virus (FIV) infection were exposed to feline herpesvirus, type 1 (FHV-1). FIV infected cats became sicker than non-FIV infected cats and required more supportive treatment. However, there were no differences in the length of their illness or in the levels and duration of FHV-1 shedding. FHV-1 infection caused a transient neutrophilia at Day 7 with a rapid return to preinfection levels. The neutrophilia coincided with a transient lymphopenia that was accompanied by a decline in both CD4+ and CD8+ T-lymphocytes. A brief decrease in the CD4+/CD8+ T-lymphocyte ratio occurred at Day 14 in both FIV infected and non-infected cats. This decrease was mainly the result of an absolute and transient increase in CD8+ T-lymphocytes. CD4+ and CD8+ T-lymphocyte numbers and CD4+/CD8+ T-lymphocyte ratios returned to baseline within 4-8 weeks in both FIV infected and non-infected cats. FIV infected cats produced less FHV-1 neutralizing antibodies during the first 3 weeks of infection than non-FIV infected animals. The IgM FHV-1 antibody response was depressed in FIV infected cats whereas the IgG antibody response was unaffected. FHV-1 infection evoked a comparable transient loss of lymphocyte blastogenic responses to concanavalin A and pokeweed mitogen in both FIV infected and non-infected cats. However, response to pokeweed mitogen took longer to return to normal in FIV infected animals. Lymphocytes from FIV infected cats had a greater and more sustained proliferative response to FHV-1 antigen than non-FIV infected cats. The ongoing IgG antibody response to FIV was not affected by FHV-1 infection.     

IgG from acutely infected cats blocks mucosal feline immunodeficiency virus infection

We have previously shown an absence of detectable systemic or local infection in cats exposed to an infectious (100 TCID(50)) feline immunodeficiency virus (FIV) plasma inoculum via either the rectal or vaginal mucosa. In contrast, this same plasma inoculum was infectious via parenteral inoculation. Moreover an equivalent dose of cell-free tissue culture-origin virus inoculum infected 100% of cats by either the rectal or vaginal exposure route. To evaluate this phenomena, we used a tissue culture system to identify a heat-stable factor in the plasma of cats acutely (3 weeks) infected with FIV that blocked infection of naive peripheral blood mononuclear cells (PBMC) by either cell-free or cell-associated FIV in vitro. A single application of as little as a 1:200 dilution of either heparinized or Alsevier's anticoagulated plasma effectively inhibited production of FIV p26 in culture over a 21-day co-culture period. Depletion of antibody using a protein A column abrogated the inhibitory effect of FIV plasma against in vitro FIV infection. Co-inoculation of heat-inactivated plasma with 400 TCID(50) FIV-B-2542 cell-free supernatant virus onto the vaginal mucosa of two cats resulted in complete inhibition of infection in one cat and increased time to infection in the second. Thus, antibody found in the plasma of cats acutely infected with FIV blocks cell-associated and cell-free infection, inhibits virus production in previously infected cells, and reduces mucosal transmission efficiency in vivo. Extrapolation may help explain the relatively inefficient mucosal transmission of human immunodeficiency virus-1 (HIV) and other lentiviruses.     

Prevalences of feline leukaemia virus and feline immunodeficiency virus infections in cats in Sydney

Objective To determine prevalences of feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) infections in ‘healthy’ cats that, through acute misadventure or other circumstance, were presented to veterinary practitioners. Prevalences of FeLV and FIV in this population were compared to those in a population of predominantly sick cats. Design and procedures Serum specimens were obtained over a 2-year period from 200 cats oldeer than 1 year of age presented to veterinary clinics for routine procedures, including cat fight injuries or abscesses, vehicular trauma, neutering, dental scaling, vaccination, grooming or boarding. An additional 894 sera were obtained over approximately the same period from specimens submitted by veterinarians to a private clinical pathology laboratory, mainly from sick cats suspected of having immune dysfunction, but including some sera from healthy cats being screened prior to FeLV vaccination. FIV antibody and FeLV antigen were detected in samples using commercial enzyme immunoassays. Results Amongst 200 ‘healthy’ cats, the prevalence of FeLV infection was 0 to 2%, and the prevalence of FIV was 6.5 to 7.5%, depending on the stringency of the criteria used to define positivity. FIV infection was significantly more prevalent in cats which resided in an inner city environment (P = 0.013). Of the 894 serum specimens submitted to the laboratory by practitioners, 11/761 (1.4%) were FeLV positive, while 148/711 (20.8%) were FIV positive. The prevalence of FIV was significantly higher in these predominantly ‘sick’ cats than in cats seen for routine veterinary procedures (P < 0.00001), while there was no difference in the prevalence of FeLV (P = 0.75) Conclusions The prevalence of FeLV and FIV in healthy cats may have been substantially overestimated in some previous Australian surveys. FeLV infection would appear to be a rare cause of disease in Australian cats. The higher prevalence of FIV positivity in sick as opposed to healthy cats infers that FIV infection contributes to the development of disease.     

Immunization-induced decrease of the CD4+:CD8+ ratio in cats experimentally infected with feline immunodeficiency virus.

In a previous experiment a group of 15 specified pathogen free (SPF) cats were experimentally infected with a Swiss isolate of feline immunodeficiency virus (FIV). A group of 15 SPF cats served as FIV negative controls. Nine cats of each group were vaccinated with a recombinant feline leukemia virus (FeLV) vaccine, six cats in each group with a placebo vaccine. All vaccinated cats developed high antibody titers to FeLV and were protected against subsequent FeLV challenge infection. In both control groups five of six cats became persistently infected with FeLV. Unexpectedly, the primary immune response to the vaccine antigen was significantly higher in the FIV positive group than in the FIV negative. The secondary response was stronger in the FIV negative cats. The goal of the present investigation was to further study the immune response in these 30 cats. They were immunized twice with the synthetic peptide L-tyrosine-L-glutamic acid-poly(DL-alanine)-poly(L-lysine) (TGAL) 21 days apart. Blood samples were collected on four occasions during the immunization process. They were tested for antibodies to TGAL, complete blood cell counts and CD4+, CD8+ and pan-T-lymphocyte counts. The following observations were made: (1) in contrast to the FeLV vaccine experiment, the primary immune response to TGAL was not significantly stronger in the FIV positive cats when tested by enzyme-linked immunosorbent assay (2). The absolute size of the CD4+ lymphocyte population was distinctly smaller in the FIV positive than in the FIV negative cats. The lowest CD4+ values were found in the dually FIV/FeLV infected cats. (3) A population of CD8+ lymphocytes was identified that was characterized by a distinctly weaker fluorescence. The size of this population increased in FIV positive and decreased in FIV negative cats during the TGAL immunization experiment. (4) The CD4+:CD8+ ratio increased in FIV negative cats during TGAL immunization from 1.9 to 2.3. In contrast, in FIV positive animals the CD4+:CD8+ ratio decreased significantly from 1.9 to 1.3 during the same period. From these and earlier data it was concluded that in short-term FIV infection the immune response to T-cell dependent antigens may be increased over that of the controls. Immune suppression develops gradually with duration of the infection. The significant drop of the CD4+:CD8+ ratio over a 5 week immunization period suggests that antigenic stimulation may accelerate the development of immune suppression in FIV positive cats. If this is a general feature, FIV infection may provide a particularly interesting model for studying the pathogenesis of AIDS.     

Enhancement after feline immunodeficiency virus vaccination.

Cats were vaccinated with one of the three preparations: purified feline immunodeficiency virus (FIV) incorporated into immune stimulating complexes (ISCOMs), recombinant FIV p24 ISCOMs, or a fixed, inactivated cell vaccine in quil A. Cats inoculated with the FIV ISCOMs or the recombinant p24 ISCOMs developed high titres of antibodies against the core protein p24 but had no detectable antibodies against the env protein gp120 or virus neutralising antibodies. In contrast, all of the cats inoculated with the fixed, inactivated cell vaccine developed anti-env antibodies and four of five had detectable levels of neutralising antibody. However, none of the vaccinated cats were protected from infection after intraperitoneal challenge with 20 infectious units of FIV. Indeed there appeared to be enhancement of infection after vaccination as the vaccinated cats become viraemic sooner than the unvaccinated controls, and 100% of the vaccinated cats became viraemic compared with 78% of the controls. The mechanism responsible for this enhancement remains unknown.     

Constitutive expression of types 1 and 2 cytokines by alveolar macrophages from feline immunodeficiency virus-infected cats

Evidence suggests that feline immunodeficiency virus (FIV), causes pulmonary immunodeficiency. The overall objective of this study was to explore FIV-induced alterations in cell counts and cytokine gene expression in the pulmonary compartment during the acute stage infection. Bronchoalveolar lavage (BAL) cells were collected from FIV-infected and control cats at 0, 4, 10, and 16 weeks post-FIV infection for phenotype and cytokine analysis. The major change in BAL cellular populations following FIV-infection was the development of a neutrophilia. Total BAL cell counts and relative numbers of alveolar macrophages (AM), eosinophils, and lymphocytes remained similar in both groups. The RT-qcPCR analyses of AM purified from BAL showed constitutive expression of TNFalpha, IL6 and IL10 mRNAs that peaked during the acute stage of infection then declined. The TNFalpha and IL6 bioactive protein secretion showed a similar response. In contrast, IFNgamma expression increased progressively with time after infection and paralleled a progressive increase in FIV-gag mRNA in AM. The IL12 p40 expression also differed from the other cytokines in that there was a progressive decrease in the number of cats with AM IL12 expression following FIV infection. Infection of AM in vitro with FIV also caused an increase in TNFalpha and IL6 mRNA and bioactive protein suggesting that the increased cytokine response by AM following infection of cats with FIV is an intrinsic characteristic of FIV-infected AM. In summary, pulmonary immune changes seen in FIV-infected cats are similar to those seen in HIV-infected human patients.     

Seroprevalence of feline immunodeficiency virus, feline leukaemia virus and Toxoplasma gondii in stray cat colonies in northern Italy and correlation with clinical and laboratory data

Stray cat colonies in urban and rural areas of Lombardy, northern Italy, were surveyed for seroprevalence of feline immunodeficiency virus (FIV) antibodies, feline leukaemia virus (FeLV) antigen and Toxoplasma gondii IgG. Of 316 cats tested, 6.6% were positive for FIV and 3.8% were positive for FeLV infection; 203 cats were tested for T gondii IgG antibodies and a prevalence of 30.5% was detected. Statistical analysis tested the influence of provenience, age, gender, health status and laboratory results on seroprevalence and found male gender and adult age were risk factors for FIV infection. FIV-infected cats were more likely to have a decreased red blood cell count than FIV seronegative cats. No predictors were significantly associated with FeLV and T gondii seropositivity. Colony cats in this study posed a limited risk for retrovirus infection to pet cats allowed outdoors, whereas toxoplasmosis exposure was comparable with the worldwide data.     

Frequent detection of papillomavirus DNA in clinically normal skin of cats infected and noninfected with feline immunodeficiency virus

Feline cutaneous squamous cell carcinomas (SCCs) often contain felis domesticus papillomavirus type 2 (FdPV‐2) DNA. While this may suggest FdPV‐2 causes feline SCC development, the proportion of cats that are asymptomatically infected by this PV is unknown. Infection by feline immunodeficiency virus (FIV) is associated with high rates of cutaneous SCC development, possibly due to increased PV infection. This study examines the frequency of cutaneous asymptomatic FdPV‐2 infections in cats and compares the rate of FdPV‐2 infection in 22 FIV‐positive cats with that in 22 FIV‐negative cats. FdPV‐2 sequences were detected in 39% of skin swabs. One or both swabs contained FdPV‐2 DNA from 52% of the cats. FIV status, age or sex of the cat did not significantly influence FdPV‐2 infection. Cats that shared a household with a PV‐infected cat could remain uninfected suggesting infection depends more on host factors than exposure to the PV. These results indicate that asymptomatic FdPV‐2 infections are common in cats, but do not provide evidence that FdPV‐2 causes feline SCC development.     

Decrease in mitogen-induced lymphocyte proliferative responses in cats infected with feline immunodeficiency virus

The blastformation tests using concanavalin A and pokeweed mitogen were carried out on peripheral blood lymphocytes obtained from cats infected with feline immunodeficiency virus (FIV). The infected cats included those showing multiple chronic disease, those with a single mild sign, and one with no clinical sign. The infected cats showed significantly lower mitogenic responses of peripheral lymphocytes to both mitogens and lower lymphocyte counts as compared to uninfected healthy cats. These immunologic alterations in the infected cats may be closely related to the development of immunodeficiency-like disorders associated with FIV.     

Comparison of T-cell subpopulations in cats naturally infected with feline leukaemia virus or feline immunodeficiency virus

T-cell subsets were studied by flow cytometry in 58 feline leukaemia virus (FeLV)-positive cats with naturally acquired FeLV infection to determine whether the changes in CD4⁺ or CD8⁺ T cell populations differed from those observed in 55 feline immunodeficiency virus (FIV)-positive cats with naturally acquired FIV infection. The sole criterion for inclusion into the study was seropositivity. Mean (SD) CD4⁺ T cell values of FeLV positive cats were decreased to 31·1 (8·0) per cent and their CD8⁺ T cell values were increased to 22·8 (6·3) per cent in comparison with uninfected control cats (37·9 [9·5] per cent CD4⁺; 15·2 [6·3] per cent CD8⁺). The CD4⁺/CD8⁺ ratio was reduced to 1·5 (0·7), compared with 3·0 (1·5) in 39 FeLv- and FIV-negative control cats. Differences from control values were significant, but there was no significant difference between CD4⁺ and CD8⁺ lymphocytes of FeLV- versus FIV-infected cats. These findings indicate that FeLv and FIV have similar effects on T lymphocyte subsets. Both retrovirus infections can induce immunodeficiency, both viruses infect a broad range of lymphohaemopoietic cells, despite having different primary target cells, and can induce the killing of lymphocytic cells in vitro. It is concluded that a decreased CD4⁺/CD8⁺ ratio is not restricted to FIV infections but may also occur in FeLv infection.     

Detection of feline immunodeficiency virus infection in bone marrow of cats.

Natural or experimental feline immunodeficiency virus (FIV) infection in cats is often associated with hematologic abnormalities which are similar to those observed in human immunodeficiency virus (HIV) infected patients. To determine if cells in bone marrow are infected with FIV and whether severity of hematopoietic disorder is correlated with the level of viral infection, bone marrow tissues from ten experimentally and two naturally FIV infected cats were examined by in situ hybridization for presence of FIV RNA. Seven of the 12 FIV infected cats were also naturally or experimentally coinfected with feline leukemia virus (FeLV). FIV RNA was detected mainly in megakaryocytes and unidentified mononuclear cells in the bone marrow of cats that were sick and had marrow hypercellularity and immaturity. These included all cats in the acute phase of FIV infection and two of seven long term FIV infected cats. One long term FIV infected cat with lymphosarcoma was also positive for FIV RNA in bone marrow cells. The other four long term FIV infected cats were relatively healthy, with normal bone marrow morphology, and were negative for FIV infected cells. Bone marrow from three non-infected and two cats infected with FeLV alone were also negative for FIV RNA by in situ hybridization. We concluded that megakaryocytes and mononuclear cells were targets of the viral infection and that the presence of FIV RNA in cells of the bone marrow correlated with marrow hypercellularity and immaturity, and severity of illness.