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

Single cell RNA-sequencing of feline peripheral immune cells with V(D)J repertoire and cross species analysis of T lymphocytes

Introduction

The domestic cat (Felis catus) is a valued companion animal and a model for virally induced cancers and immunodeficiencies. However, species-specific limitations such as a scarcity of immune cell markers constrain our ability to resolve immune cell subsets at sufficient detail. The goal of this study was to characterize circulating feline T cells and other leukocytes based on their transcriptomic landscape and T-cell receptor repertoire using single cell RNA-sequencing.

Methods

Peripheral blood from 4 healthy cats was enriched for T cells by flow cytometry cell sorting using a mouse anti-feline CD5 monoclonal antibody. Libraries for whole transcriptome, alpha/beta T cell receptor transcripts and gamma/delta T cell receptor transcripts were constructed using the 10x Genomics Chromium Next GEM Single Cell 5' reagent kit and the Chromium Single Cell V(D)J Enrichment Kit with custom reverse primers for the feline orthologs.

Results

Unsupervised clustering of whole transcriptome data revealed 7 major cell populations - T cells, neutrophils, monocytic cells, B cells, plasmacytoid dendritic cells, mast cells and platelets. Sub cluster analysis of T cells resolved naive (CD4+ and CD8+), CD4+ effector T cells, CD8+ cytotoxic T cells and gamma/delta T cells. Cross species analysis revealed a high conservation of T cell subsets along an effector gradient with equitable representation of veterinary species (horse, dog, pig) and humans with the cat. Our V(D)J repertoire analysis demonstrated a skewed T-cell receptor alpha gene usage and a restricted T-cell receptor gamma junctional length in CD8+ cytotoxic T cells compared to other alpha/beta T cell subsets. Among myeloid cells, we resolved three clusters of classical monocytes with polarization into pro- and anti-inflammatory phenotypes in addition to a cluster of conventional dendritic cells. Lastly, our neutrophil sub clustering revealed a larger mature neutrophil cluster and a smaller exhausted/activated cluster.

Discussion

Our study is the first to characterize subsets of circulating T cells utilizing an integrative approach of single cell RNA-sequencing, V(D)J repertoire analysis and cross species analysis. In addition, we characterize the transcriptome of several myeloid cell subsets and demonstrate immune cell relatedness across different species.

Combination Antiretroviral Therapy and Immunophenotype of Feline Immunodeficiency Virus

Feline Immunodeficiency Virus (FIV) causes progressive immune dysfunction in cats similar to human immunodeficiency virus (HIV) in humans. Although combination antiretroviral therapy (cART) is effective against HIV, there is no definitive therapy to improve clinical outcomes in cats with FIV. This study therefore evaluated pharmacokinetics and clinical outcomes of cART (2.5 mg/kg Dolutegravir; 20 mg/kg Tenofovir; 40 mg/kg Emtricitabine) in FIV-infected domestic cats. Specific pathogen free cats were experimentally infected with FIV and administered either cART or placebo treatments (n = 6 each) for 18 weeks, while n = 6 naïve uninfected cats served as controls. Blood, saliva, and fine needle aspirates from mandibular lymph nodes were collected to quantify viral and proviral loads via digital droplet PCR and to assess lymphocyte immunophenotypes by flow cytometry. cART improved blood dyscrasias in FIV-infected cats, which normalized by week 16, while placebo cats remained neutropenic, although no significant difference in viremia was observed in the blood or saliva. cART-treated cats exhibited a Th2 immunophenotype with increasing proportions of CD4+CCR4+ cells compared to placebo cats, and cART restored Th17 cells compared to placebo-treated cats. Of the cART drugs, dolutegravir was the most stable and long-lasting. These findings provide a critical insight into novel cART formulations in FIV-infected cats and highlight their role as a potential animal model to evaluate the impact of cART on lentiviral infection and immune dysregulation.

Risk factors of Bartonella spp. infection and the association between Bartonella spp. and T-lymphocyte subset alteration in asymptomatic retrovirus-infected cats in Bangkok Metropolitan, Thailand

Background and Aim: Cats are a reservoir for Bartonella spp. infection in humans. Human bartonellosis causes disseminated inflammation to develop in immunocompromised patients, such as those infected with human immunodeficiency virus. However, the associated risks of Bartonella spp. infection in immunocompromised retroviral-infected cats have been inconclusive. This study aimed to evaluate the associated risks of Bartonella spp. infection with the alteration of T-lymphocyte subsets of retroviral-infected cats. Materials and Methods: We collected blood samples from 161 client-owned cats at veterinary clinics and hospitals throughout the Bangkok Metropolitan area from 2017 to 2020. The samples underwent hematological biochemical tests, feline retroviral status evaluation, Bartonella spp. polymerase chain reaction assay, immunofluorescence assay, and CD4+ and CD8+ lymphocyte counts. Risk factors associated with Bartonella spp. infection were determined by odds ratio (OR). Hematological and biochemical parameters were compared using independent t-tests. CD4+ and CD8+ lymphocyte counts and the CD4+/CD8+ ratio were compared among groups classified according to their retroviral and Bartonella spp. infection status. Results: The prevalence of Bartonella spp. in our study cohort was 16.1%, and the seroprevalence was 94.9%. Cats aged >1 year were at a higher risk of seropositivity than cats aged <1 year (OR: 4.296, 95% confidence interval: 1.010–18.275). The CD8+ percentage was significantly higher in seropositive cats (p = 0.026). There was a significant reduction in the CD4+/CD8+ ratio between cats negative for both retrovirus and Bartonella spp. infection and cats with concurrent retrovirus and Bartonella spp. infection (p = 0.041). Conclusion: In endemic countries or areas, cat owners must be made aware of the risk of exposure to Bartonella spp. due to the high rate of bacteremia and seroprevalence. Retrovirus-infected cats with concurrent Bartonella spp. infection also showed a significant, inverted CD4+/CD8+ ratio, which may be used as a novel marker in bartonellosis. Similar studies focusing on the different stages of retrovirus infection should be undertaken further to elucidate the effect of retrovirus infection on Bartonella spp. infection.

Clinicopathological and Epidemiological Findings in Pet Cats Naturally Infected with Feline Immunodeficiency Virus (FIV) in Australia

Feline immunodeficiency virus (FIV) infection in experimentally infected domestic cats produces characteristic clinical manifestations including hematological changes, neurological disease, neoplasia (most notably lymphoma) and lymphopenia-mediated immunodeficiency predisposing cats to a range of secondary infections. Conflicting reports exist, however, with regard to disease associations and survival time in naturally FIV-infected cats. The purpose of this retrospective case−control study was to investigate the effect of natural FIV infection on hematological, blood biochemical and urinalysis parameters and survival time in three cohorts of pet cats in Australia. Cohorts 1 and 2 were recruited from a large veterinary hospital in Melbourne, Victoria (n = 525 and 282), while a third cohort consisted of cats recruited from around Australia as part of a FIV field vaccine efficacy trial (n = 425). FIV-infected cats in cohorts 1, 2 and 3 were found to have 15/37 (41%), 13/39 (33%) and 2/13 (15%) clinicopathological parameters significantly different to FIV-uninfected cats, respectively. Two changes in FIV-infected cats in cohort 1, hypochromia (low hemoglobin) and hyperglobulinemia, were outside the supplied reference intervals and should serve as diagnostic triggers for FIV testing. Kaplan−Meier survival analysis of cats in cohorts 1 and 2 combined did not find any difference between FIV-infected and FIV-uninfected cats, however a confounding factor was a large euthanasia rate within the first 12 months in both groups. Three significant (p < 0.05) spatial clusters of FIV infection were identified in Melbourne. A possible relationship between FIV infection status and socioeconomic disadvantage was discovered, based on three government indices of socioeconomic status (p < 0.001). Until longitudinal field studies are performed in Australia to further investigate the long-term effects of natural FIV infection, Australian veterinarians should consider FIV to be an important infection of pet cats, and recommend measures to prevent FIV infection.

Vaccination of Immunocompromised Cats

Immunocompromise is a common condition in cats, especially due to widespread infections with immunosuppressive viruses, such as feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV), but also due to chronic non-infectious diseases, such as tumours, diabetes mellitus, and chronic kidney disease, as well as treatment with immunosuppressive drugs, such as glucocorticoids, cyclosporins, or tumour chemotherapy. In this review, the European Advisory Board on Cat Diseases (ABCD), a scientifically independent board of experts in feline medicine from eleven European countries, discusses the current knowledge and rationale for vaccination of immunocompromised cats. So far, there are few data available on vaccination of immunocompromised cats, and sometimes studies produce controversial results. Thus, this guideline summarizes the available scientific studies and fills in the gaps with expert opinion, where scientific studies are missing. Ultimately, this review aims to help veterinarians with their decision-making in how best to vaccinate immunocompromised cats.

2020 AAFP Feline Retrovirus Testing and Management Guidelines

CLINICAL IMPORTANCE

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) infections are found in cats worldwide. Both infections are associated with a variety of clinical signs and can impact quality of life and longevity.

SCOPE

This document is an update of the 2008 American Association of Feline Practitioners' feline retrovirus management guidelines and represents current knowledge on pathogenesis, diagnosis, prevention and treatment of retrovirus infections in cats.

TESTING AND INTERPRETATION

Although vaccines are available for FeLV in many countries and for FIV in some countries, identification of infected cats remains an important factor for preventing new infections. The retrovirus status of every cat at risk of infection should be known. Cats should be tested as soon as possible after they are acquired, following exposure to an infected cat or a cat of unknown infection status, prior to vaccination against FeLV or FIV, and whenever clinical illness occurs. It might not be possible to determine a cat's infection status based on testing at a single point in time; repeat testing using different methods could be required. Although FeLV and FIV infections can be associated with clinical disease, some infected cats, especially those infected with FIV, can live for many years with good quality of life.

MANAGEMENT OF INFECTED CATS

There is a paucity of data evaluating treatments for infected cats, especially antiretroviral and immunomodulatory drugs. Management of infected cats is focused on effective preventive healthcare strategies, and prompt identification and treatment of illness, as well as limiting the spread of infection.

Hematological findings and factors associated with feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) positivity in cats from southern Brazil

ABSTRACT: Using a retrospective study, 493 cats tested for FeLV and FIV were selected for analysis of the association between hematologic findings and positivity at immunoassay test. Individual and hematologic variables were assessed considering the influence of results using univariate and multivariate logistic regression analysis. Out 153 of the 493 cats were positive for FeLV (31%), 50 were positive for FIV (10.1%) and 22 were positive for both FIV and FeLV (4.4%). Multivariate analysis detected significant associations between FeLV infection and age below 1 year (p=0.01), age from 1 to 10 years (p=0.03), and crossbreed (p=0.04). Male cats were more likely to be FIV-positive (p=0.002). Regarding hematological changes, FeLV-positive cats have higher odds to anemia, leukopenia and lymphopenia than FeLV-negative cats. FIV-positive cats are more likely to have anemia than negative. Identification of associated factors related to animal status and correlation of hematological disorders with infection by retroviruses in cats could be useful for detecting these retroviral diseases in cats.

Prevalence of selected rickettsial infections in cats in Southern Germany

Prevalence of Anaplasma, Ehrlichia, Neorickettsia, and Wolbachia DNA in blood of 479 cats collected in different veterinary clinics in Southern Germany was determined using a previously published conventional PCR using 16S-23S intergenic spacer primers (5' CTG GGG ACT ACG GTC GCA AGA C 3' - forward; 5' CTC CAG TTT ATC ACT GGA AGT T 3' - reverse). Purified amplicons were sequenced to confirm genus and species. Associations between rickettsial infections, and feline immunodeficiency virus (FIV), as well as feline leukemia virus (FeLV) status were evaluated. Rickettsial prevalence was 0.4% (2/479; CI: 0.01-1.62%). In the two infected cats, Anaplasma phagocytophilum DNA was amplified. These cats came from different environment and had outdoor access. Both were ill with many of their problems likely related to other diseases. However, one cat had neutrophilia with left shift and the other thrombocytopenia potentially caused by their A. phagocytophilum infection. There was no significant difference in the FIV and FeLV status between A. phagocytophilum-negative and -positive cats. A. phagocytophilum can cause infection in cats in Southern Germany, and appropriate tick control is recommended.

Sequence variation of the feline immunodeficiency virus genome and its clinical relevance

The ongoing evolution of feline immunodeficiency virus (FIV) has resulted in the existence of a diverse continuum of viruses. FIV isolates differ with regards to their mutation and replication rates, plasma viral loads, cell tropism and the ability to induce apoptosis. Clinical disease in FIV-infected cats is also inconsistent. Genomic sequence variation of FIV is likely to be responsible for some of the variation in viral behaviour. The specific genetic sequences that influence these key viral properties remain to be determined. With knowledge of the specific key determinants of pathogenicity, there is the potential for veterinarians in the future to apply this information for prognostic purposes. Genomic sequence variation of FIV also presents an obstacle to effective vaccine development. Most challenge studies demonstrate acceptable efficacy of a dual-subtype FIV vaccine (Fel-O-Vax FIV) against FIV infection under experimental settings; however, vaccine efficacy in the field still remains to be proven. It is important that we discover the key determinants of immunity induced by this vaccine; such data would compliment vaccine field efficacy studies and provide the basis to make informed recommendations on its use.

Clinical aspects of feline retroviruses: a review

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses with global impact on the health of domestic cats. The two viruses differ in their potential to cause disease. FeLV is more pathogenic, and was long considered to be responsible for more clinical syndromes than any other agent in cats. FeLV can cause tumors (mainly lymphoma), bone marrow suppression syndromes (mainly anemia), and lead to secondary infectious diseases caused by suppressive effects of the virus on bone marrow and the immune system. Today, FeLV is less commonly diagnosed than in the previous 20 years; prevalence has been decreasing in most countries. However, FeLV importance may be underestimated as it has been shown that regressively infected cats (that are negative in routinely used FeLV tests) also can develop clinical signs. FIV can cause an acquired immunodeficiency syndrome that increases the risk of opportunistic infections, neurological diseases, and tumors. In most naturally infected cats, however, FIV itself does not cause severe clinical signs, and FIV-infected cats may live many years without any health problems. This article provides a review of clinical syndromes in progressively and regressively FeLV-infected cats as well as in FIV-infected cats.

Clinical aspects of feline immunodeficiency and feline leukemia virus infection

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses with a global impact on the health of domestic cats. The two viruses differ in their potential to cause disease. FIV can cause an acquired immunodeficiency syndrome that increases the risk of developing opportunistic infections, neurological diseases, and tumors. In most naturally infected cats, however, FIV itself does not cause severe clinical signs, and FIV-infected cats may live many years without any health problems. FeLV is more pathogenic, and was long considered to be responsible for more clinical syndromes than any other agent in cats. FeLV can cause tumors (mainly lymphoma), bone marrow suppression syndromes (mainly anemia) and lead to secondary infectious diseases caused by suppressive effects of the virus on bone marrow and the immune system. Today, FeLV is less important as a deadly infectious agent as in the last 20 years prevalence has been decreasing in most countries.

The role of flow cytometry in companion animal diagnostic medicine

Flow cytometry is a powerful tool for characterising the composition of complex cell populations. The accuracy and precision of this technology for describing and enumerating cells exceeds traditional methods. The number of diagnostic veterinary laboratories with access to a dedicated machine is increasing, and there is the potential to offer a clinical flow cytometry service. The improved availability of monoclonal antibodies (mAb) to cell markers expressed by the leukocytes of companion animals, permits the implementation of comprehensive mAb panels suitable for diagnosis of lympho- and myeloproliferative disease. Reticulated erythrocyte and platelet quantification, antiglobulin assays for immune-mediated cytopenias, lymphocyte subset analysis, and immunophenotyping of lymphoma and leukemia, have been validated for companion animal samples on the flow cytometer. It is now timely to consider the role of flow cytometry in diagnostic practice, and the requirement for quality assurance and standardization of testing procedures.

IMMUNODEFICIENCY ASSOCIATED WITH MULTIPLE CONCURRENT INFECTIONS IN CAPTIVE PALLAS' CATS (OTOCOLOBUS MANUL)

Five neonatal Pallas' cats (Otocolobus manul) at the Oklahoma City Zoo died from toxoplasmosis with concurrent herpesvirus infection. These multiple infections suggested underlying immunodeficiency, perhaps caused by concurrent infection with feline immunodeficiency virus (FIV); so blood samples were collected for serology, serum protein electrophoresis, lymphocyte proliferation assays, and cytokine analysis by reverse transcriptase-quantitative competitive polymerase chain reaction (RT-qcPCR). Resulting data were compared with data from FIV-infected and control domestic short-haired cats. In addition, peripheral blood mononuclear cell cultures were propagated to detect FIV virus by both RT-qcPCR and detection of reverse transcriptase activity. Serum protein electrophoresis showed that four of six Pallas' cats had increased alpha, globulins. At least two Pallas' cats had decreased lymphoproliferation responses to mitogen. and all three tested animals exhibited defective interleukin-12 gene expression. Although these clinical and laboratory findings suggested an immunodeficiency syndrome, FIV infection could not be confirmed. On the basis of repeated blood test results, it can be concluded that nutritional, metabolic, or other systemic problems probably did not contribute to the disease syndrome. Further investigation of other possible causes of immunodeficiency, including a possible genetic component, in this population is needed.

A standardized gating technique for the generation of flow cytometry data for normal canine and normal feline blood lymphocytes

Flow cytometry is becoming a commonly used technique to characterize a variety of cells. It provides a powerful application to rapidly determine the relative percentages of T-lymphocyte subsets and B-lymphocytes. The effectiveness of its application, however, is dependent on standardization, especially in a clinical setting. Application of flow cytometry to veterinary diagnostics has been limited by the unavailability of reagents and by the unstandardized characterization of normal values using antibodies not commercially available, but typically provided through the generosity of other researchers. This paper presents a standardized gating protocol, and average values and ranges observed for normal canine and feline blood lymphocytes using commercially available antibodies to cell surface markers for CD5, CD3, CD4, CD8, MHC II, and B lymphocytes. The averages for these markers on gated lymphocytes were as follows: Canine CD5 83.3%, Canine CD4 45.0%, Canine CD8 28.8%, Canine MHC II 98.0%, Canine B Cell 12.9%, Canine CD4/CD8 ratio 1.87, Feline T lymphocytes 77.3%, Feline CD4 44.5%, Feline CD8 25.7%, Feline B Cell 24.1%, Feline CD4/CD8 Ratio 1.75. Normal values were also established for a mixed breed group of dogs, and old versus young dogs. This information will provide researchers and clinicians with a standardized protocol for gating, which establishes a basis for comparison between techniques, and a measure of phenotypic percentages for flow cytometry in normal dogs and cats based on this standardization and commercially available antibodies.

Some aspects of humoral and cellular immunity in naturally occuring feline infectious peritonitis

Haematology, antibody titers and serum protein electrophoresis from 48 cats (34 effusive and 14 noneffusive forms) affected with feline infectious peritonitis (FIP) were studied and compared with those of 20 healthy cats. In the effusive form, antibody titers and protein electrophoresis in the effusions were analyzed. The distribution of the immune cells and of the virus in FIP lesions were also investigated immunohistochemically with the avidin-biotin complex (ABC) method, using antibodies against the FIP virus (FIPV), myelomonocytic (MAC387) and lymphoid (CD3, CD4 and CD8 for T-cells and IgM and IgG for B-cells) antigens. Seropositive animals (antibody titer>1:100) were present among both the FIP infected cats (73%) and the healthy cats (70%). Cats with effusive FIP had neutrophilic leukocytosis (P>0.05), lymphopenia (P<0.01) and eosinopenia (P<0.001). In both effusive and noneffusive forms decreased albumin/globulin ratio (P<0.001) with hypoalbuminemia (P<0.001), hyperglobulinemia (P<0.001) and increased alpha2- (P<0.05), beta- (P<0.05) and gamma-globulins (P<0.001) were found. Hypergammaglobulinemia was not related to the antibody titers, suggesting the presence of other proteins with gamma-motility (e.g. complement fractions). The electrophoretic pattern of the effusions was always similar to that of the corresponding serum. Antibody titers higher than those of the corresponding serum were often detected in the effusions. Immunohistochemical findings were not related to the antibody titers, but they were related to the histological aspect of the lesions. In cellular foci of FIP lesions many virus-infected macrophages and few lymphocytes, mainly CD4+, were found. Extracellular viral and myelomonocytic antigens were also detectable in the foci with intercellular necrosis. Only few FIPV-infected cells were present at the periphery of the larger necrotic foci: in these lesions MAC387+ cells were mainly neutrophils, with many MAC387 macrophages, probably due to their activated state; a small number of lymphocytes, with an increasing percentage of CD8+ cells was present. Lymphocytes were more abundant when cellular foci and FIP-infected macrophages were centered around neoformed vessels. IgM and IgG exposing B-cells were always few and scattered. In conclusion the simultaneous analysis of body fluids and of the cellular composition of the lesions showed a complex immune status, on which type III and type IV hypersensitivity could coexist.