Systemic immunosuppression depletes peripheral blood regulatory B cells in patients with immune thrombocytopenia.

Regulatory B (Breg) cells are potentially implicated in the pathogenesis of immune thrombocytopenia (ITP). We analysed a prospective cohort of newly diagnosed steroid naïve ITP patients enrolled in the multicentre FLIGHT trial and found that the numbers of Bregs in their peripheral blood were similar to healthy controls. In contrast, Breg numbers were significantly reduced in ITP patients treated with systemic immunosuppression (glucocorticoids or mycophenolate mofetil). We also demonstrate that glucocorticoid treatment impairs Breg interleukin-10 production via an indirect T-cell-mediated mechanism.

Feline precision medicine using whole-exome sequencing identifies a novel frameshift mutation for vitamin D-dependent rickets type 2.

OBJECTIVES: A 14-week-old female domestic longhair kitten presented with shifting lameness and disproportionately smaller size compared with a co-housed littermate. METHODS: Hematology and serum biochemical testing were conducted to investigate causes for delayed growth, and radiographs of the appendicular skeleton were obtained. RESULTS: The afflicted kitten had marked hypocalcemia, mild hypophosphatemia and substantial elevations in alkaline phosphatase activity, as well as pathognomonic radiographic findings consistent with rickets. Skeletal changes and hypocalcemia prompted testing of concentrations of parathyroid hormone (PTH) and vitamin D metabolites. Endocrine testing demonstrated significant increases in serum concentrations of PTH and 1,25-dihydroxycholecalciferol (calcitriol), supporting a diagnosis of vitamin D-dependent rickets type 2. Provision of analgesia, supraphysiologic doses of calcitriol and calcium carbonate supplementation achieved normalization of the serum calcium concentration and restoration of normal growth, although some skeletal abnormalities persisted. Once skeletally mature, ongoing calcitriol supplementation was not required. Whole-exome sequencing (WES) was conducted to identify the underlying DNA variant. A cytosine deletion at cat chromosome position B4:76777621 in VDR (ENSFCAT00000029466:c.106delC) was identified and predicted to cause a stop codon in exon 2 (p.Arg36Glufs*18), disrupting >90% of the receptor. The variant was unique and homozygous in this patient and absent in the sibling and approximately 400 other cats for which whole-genome and whole-exome data were available. CONCLUSIONS AND RELEVANCE: A unique, heritable form of rickets was diagnosed in a domestic longhair cat. WES identified a novel frameshift mutation affecting the gene coding for the vitamin D3 receptor, determining the likely causal genetic variant. Precision medicine techniques, including whole-exome and whole-genome sequencing, can be a standard of care in cats to identify disease etiologies, and to target therapeutics and personalize treatment.

CTSK variant implicated in suspected pyknodysostosis in a domestic cat.

Case summary: A 9-month-old entire male domestic longhair cat presented with a history of pathological fractures, chronic musculoskeletal pain and poor growth. Multiple facial and skeletal abnormalities were identified on physical examination and advanced imaging (CT and radiographs). A variant in CTSK was identified in the affected cat following whole-exome sequencing (WES). The cat was managed symptomatically with diet, environmental modifications and analgesia. Relevance and novel information: This is the first report of a cat with a similar clinical presentation and genetic variant to the hereditary human genetic disorder pyknodysostosis. In this case, WES was performed, which often facilitates the diagnosis of various hereditary disorders (ie, a conceptual framework for practicing feline genomic medicine). Despite the severe skeletal and appendicular abnormalities described, the cat was alive more than 2 years after its initial presentation.

Epigenetic drug screen identified IOX1 as an inhibitor of Th17-mediated inflammation through targeting TET2.

BACKGROUND: Targeting helper T cells, especially Th17 cells, has become a plausible therapy for many autoimmune diseases. METHODS: Using an in vitro culture system, we screened an epigenetics compound library for inhibitors of IFN-γ and IL-17 expression in murine Th1 and Th17 cultures. FINDINGS: This identified IOX1 as an effective suppressor of IL-17 expression in both murine and human CD4+ T cells. Furthermore, we found that IOX1 suppresses Il17a expression directly by targeting TET2 activity on its promoter in Th17 cells. Using established pre-clinical models of intraocular inflammation, treatment with IOX1 in vivo reduced the migration/infiltration of Th17 cells into the site of inflammation and tissue damage. INTERPRETATION: These results provide evidence of the strong potential for IOX1 as a viable therapy for inflammatory diseases, in particular of the eye. FUNDING: This study was supported by the National Key Research and Development Program of China 2021YFA1101200 (2021YFA1101204) to LW and XW; the National Natural Science Foundation of China 81900844 to XH and 82171041 to LW; the China Postdoctoral Science Foundation 2021M700776 and the Scientific Research Project of Guangdong Provincial Bureau of Traditional Chinese Medicine 20221373 to YZ; and the National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS (National Health Service) Foundation Trust and University College London Institute of Ophthalmology, UK (DAC, LPS, PJPL, MS, ADD and RWJL). The views expressed are those of the authors and not necessarily those of the NIHR or the UK's Department of Health and Social Care.

Prevalence of Babesia spp. pathogens in the ticks Dermacentor reticulatus and Ixodes ricinus in the UK.

The emergence of Babesia pathogens novel to the UK is of growing concern; these include Babesia canis and Babesia caballi. However, a better understanding of changes in the prevalence of endemic Babesia species such as Babesia venatorum and Babesia divergens is also of importance. Here, the prevalence of Babesia pathogens in both Dermacentor reticulatus and Ixodes ricinus ticks was assessed. Dermacentor reticulatus were collected from six sites known to harbour populations of this species in west Wales and southern England. DNA was extracted from 879 individual ticks and subjected to PCR and sequence analysis. Seven Babesia species were detected in 7.5% of the ticks, including B. caballi (0.68%), B. bovis (1.7%), B. microti (1.02%), B. bigemina (0.34%), B. capreoli (0.34%), and one isolate of B. canis (0.34%). Two of the field sites with grazing equines present had ticks that were positive for B. caballi. For I. ricinus, up to 200 nymphs were collected from each of 24 cattle farms in south-west England. Nymphs were divided into 6 pools of 30 from each farm for DNA extraction, PCR, and sequencing. Samples from seven out of the 24 farms tested positive for Babesia, and most were positive for more than one species. Babesia divergens was identified from five farms, and three of these farms had two pooled samples positive for B. divergens, which given the low overall prevalence rate suggests that B. divergens may be highly clustered within the tick population. Most of the remaining positive samples were Babesia venatorum, demonstrating that this zoonotic pathogen is widespread in livestock habitats. The data suggest that B. canis is not yet widely prevalent in established D. reticulatus populations in the UK, but that there is a need to raise awareness of the risk of equine piroplasmosis in areas with endemic D. reticulatus foci, since B. caballi appears more widely established.

Lack of association between feline AB blood groups and retroviral status: a multicenter, multicountry study.

OBJECTIVES: The relationship between blood group antigens and disease has been studied in humans. Blood types have been associated with both decreased and increased rates of various infections. In addition, blood group expression has been shown to vary with some cancers and gastrointestinal diseases. The objective of this study was to explore whether there is a relationship between blood type and retroviral infections in cats. METHODS: Case records from a veterinary research laboratory, veterinary teaching hospitals and veterinary blood banks were retrospectively searched for cats where both blood type and retroviral status (feline leukemia [FeLV], feline immunodeficiency virus [FIV] or both) were listed (part 1). In addition, a sample of 33 cats with confirmed FIV infection was genotyped to determine blood groups (part 2). RESULTS: In part 1, 709 cats were identified, 119 of which were positive for retroviral infection. Among all cases, 621 were type A (87.6%), 68 were type B (9.6%) and 20 were type AB (2.8%). There was no relationship between overall retroviral status (positive/negative) and blood type (P = 0.43), between FeLV status and blood type (P = 0.86) or between FIV status and blood type (P = 0.94). There was no difference in the distribution of blood types between cats that were healthy and typed as possible blood donors vs sick cats that were typed prior to a possible transfusion (P = 0.13). In part 2, of the 33 FIV-infected cats, all blood group genotypes were identified, although this test did not discriminate type A from type AB. CONCLUSIONS AND RELEVANCE: No relationship was identified between feline retroviral status and blood type in this study. The relationship between blood type and other disease states requires further study in veterinary patients.

Glucocorticoid treatment in patients with newly diagnosed immune thrombocytopenia switches CD14++ CD16+ intermediate monocytes from a pro-inflammatory to an anti-inflammatory phenotype.

Immune thrombocytopenia (ITP) is thought to result from an aberrant adaptive autoimmune response, involving autoantibodies, B and T lymphocytes, directed at platelets and megakaryocytes. Previous reports have demonstrated skewed CD4+ T-helper subset distribution and enhanced production of pro-inflammatory cytokines such as interleukin 17A and interferon gamma. The role of monocytes (MCs) in ITP is less widely described, but innate immune cells have a role in shaping CD4+ T-cell phenotypes. Glucocorticoids (GCs) are commonly used for first-line ITP treatment and modulate a broad range of immune cells including T cells and MCs. Using multiparameter flow cytometry analysis, we demonstrate the expansion of intermediate MCs (CD14++ CD16+ ) in untreated patients with newly diagnosed ITP, with these cells displaying a pro-inflammatory phenotype, characterised by enhanced expression of CD64 and CD80. After 2 weeks of prednisolone treatment (1 mg/kg daily), the proportion of intermediate MCs reduced, with enhanced expression of the anti-inflammatory markers CD206 and CD163. Healthy control MCs were distinctly different than MCs from patients with ITP before and after GC treatment. Furthermore, the GC-induced phenotype was not observed in patients with chronic ITP receiving thrombopoietin receptor agonists. These data suggest a role of MCs in ITP pathogenesis and clinical response to GC therapy.

Molecular detection of hemotropic mycoplasmas (hemoplasmas) in domestic cats (Felis catus) in Romania.

BACKGROUND: The hemotropic mycoplasmas (hemoplasmas) of the genus Mycoplasma are recognized as important bacteria that parasitize red blood cells, causing hemolytic anemia in many mammalian species, including cats. No information is available concerning the presence of feline hemoplasma infections in cats in Romania. Thus, the objective of the present study was to provide data on the occurrence and molecular characterization of hemotropic mycoplasmas in client-owned cats in Romania. METHODS: Blood samples from 51 unhealthy cats, originating from Timisoara Municipality, Romania, were screened for the presence of hemoplasmas using conventional polymerase chain reaction (PCR) targeting the 16S rRNA gene and sequencing assays. PCR-positive samples were subsequently analyzed by phylogenetic and population genetic analysis. RESULTS: Molecular analysis revealed 11 (21.6%) positive samples, consisting of 8 (72.7%) Candidatus Mycoplasma haemominutum and 3 (27.3%) Mycoplasma haemofelis confirmed positives. Candidatus Mycoplasma turicensis was not detected, and no co-infections were registered. No significant associations (p > 0.05) were found between the hemoplasma infection status and age, gender, breed, presence of ectoparasites, feline leukemia virus/feline immunodeficiency virus positivity of cats, or the sampling season. However, outdoor access was positively associated (p = 0.049) with infection and could be considered a risk factor (OR = 4.1) in acquiring feline hemotropic mycoplasmas. Phylogenetic analysis revealed that our sequences clustered with those selected from the GenBank database in two distinct clades. The registered population genetic indices were strongly supportive of the great variance in sequences between the recorded Mycoplasma species. CONCLUSIONS: The findings support the occurrence of feline hemoplasma infections in previously uninvestigated territories of Europe, providing useful information for small animal practitioners. To our knowledge, the present survey is the first reported molecular evidence of feline hemoplasma infections in Romania.

Evaluation of Interferon-Gamma Polymorphisms as a Risk Factor in Feline Infectious Peritonitis Development in Non-Pedigree Cats-A Large Cohort Study.

Feline infectious peritonitis (FIP) is a common infectious cause of death in cats, with heritable host factors associated with altered risk of disease. To assess the role of feline interferon-gamma gene (fIFNG) variants in this risk, the allele frequencies of two single nucleotide polymorphisms (SNPs) (g.401 and g.408) were determined for non-pedigree cats either with confirmed FIP (n = 59) or from the general population (cats enrolled in a large lifetime longitudinal study; n = 264). DNA was extracted from buccal swabs or tissue samples. A pyrosequencing assay to characterize the fIFNG SNPs was designed, optimized and subsequently performed on all samples. Genotype and allele frequency were calculated for each population. Characterization of the target SNPs was possible for 56 of the cats with FIP and 263 of the cats from the general population. The SNPs were in complete linkage disequilibrium with each other. There was an association between FIP status and genotype (χ2; p = 0.028), with a reduced risk of developing FIP (χ2; p = 0.0077) associated with the genotype TT at both positions. These results indicate that, although fIFNG variants may be associated with altered risk of disease, the prevalence of individual variants within both populations limits application of their characterization to breeding purposes.

IL-10 and IL-17 expression by CD4+ T cells is altered in corticosteroid refractory immune thrombocytopenia (ITP).

BACKGROUND: Corticosteroids remain the first-line treatment for patients with immune thrombocytopenia (ITP). However, 20% to 30% of patients do not respond to treatment at tolerable doses. This variation in corticosteroid efficacy is replicated in other autoimmune diseases and may have an adaptive immune basis. OBJECTIVE: To test the hypothesis that CD4+ T-cell responses to corticosteroids are different in patients with clinically defined corticosteroid refractory ITP. METHODS: In this prospective cohort study, CD4+ T cells from patients with ITP were cultured in the presence or absence of dexamethasone (Dex). Intracellular cytokine expression was then quantified by flow cytometry and compared with patients' clinical response to corticosteroid treatment. A control cohort of patients with autoimmune uveitis was also studied to evaluate whether our findings were limited to ITP or are potentially generalizable across autoimmune diseases. RESULTS: The ratio of interleukin (IL)-10 to IL-17 expression following CD4+ T cell culture with Dex was able to discriminate between ITP patients with a clinically defined complete (n = 33), partial (n = 12) or nonresponse (n = 11) to corticosteroid treatment (P = .002). These findings were replicated in patients with autoimmune uveitis (complete response n = 14, nonresponse n = 22; P = .01). CONCLUSIONS: There is a relative abrogation of IL-10 and persistence of IL-17 expression in the CD4+ T cells of patients who clinically fail corticosteroid therapy. This observation has potential to inform both our mechanistic understanding of the action of corticosteroids in the treatment of ITP, and as a biomarker for steroid refractory disease, with potential application across a range of hematological and nonhematological conditions.

Ex Vivo T Cell Cytokine Expression Predicts Survival in Patients with Severe Alcoholic Hepatitis.

Alcoholic hepatitis (AH) is an acute inflammatory liver condition with high early mortality rate. Steroids improve short-term survival but nonresponders have the worst outcomes. There is a clinical need to identify these high-risk individuals at the time of presentation. T cells are implicated in AH and steroid responsiveness. We measured ;ex vivo T cell cytokine expression as a candidate biomarker of outcomes in patients with AH. Consecutive patients (bilirubin >80 µmol/L and ratio of aspartate aminotransferase to alanine aminotransferase >1.5 who were heavy alcohol consumers with discriminant function [DF] ≥32), were recruited from University Hospitals Plymouth NHS Trust. T cells were obtained and stimulated ;ex vivo. Cytokine expression levels were determined by flow cytometry and protein multiplex analysis. Twenty-three patients were recruited (10 male; median age 51 years; baseline DF 67; 30% 90-day mortality). Compared to T cells from nonsurvivors at day 90, T cells from survivors had higher baseline baseline intracellular interleukin (IL)-10:IL-17A ratio (0.43 vs 1.20, p=0.02). Multiplex protein analysis identified interferon γ (IFNγ) and tumor necrosis factor-α (TNF-α) as independent predictors of 90-day mortality (p=0.04, p=0.01, respectively). The ratio of IFNγ to TNF-α was predictive of 90-day mortality (1.4 vs 0.2, p=0.03). These data demonstrate the potential utility of T cell cytokine release assays performed on pretreatment blood samples as biomarkers of survival in patients with severe AH. Our key findings were that intracellular IL-10:IL-17A and IFNγ:TNF-α in culture supernatants were predictors of 90-day mortality. This offers the promise of developing T cell-based diagnostic tools for risk stratification.

Intermediate Monocytes in Acute Alcoholic Hepatitis Are Functionally Activated and Induce IL-17 Expression in CD4+ T Cells.

In humans, the three main circulating monocyte subsets are defined by their relative cell surface expression of CD14 and CD16. They are all challenging to study because their characteristics are strongly context specific, and this has led to a range of conflicting reports about their function, which is especially so for CD14++CD16+ (intermediate) monocytes. Ex vivo cultures are also often confounded by the concomitant use of immunosuppressive drugs. We therefore sought to characterize the phenotype and function of intermediate monocytes in the setting of acute inflammation prior to treatment in a cohort of 41 patients with acute alcoholic hepatitis (AH). Circulating intermediate monocytes were enriched in patients with AH and had an activated phenotype with enhanced expression of CCR2 and CD206 compared with healthy controls. Proinflammatory cytokine expression, including IL-1ß and IL-23, was also higher than in healthy controls, but both classical (CD14++CD16-) and intermediate monocytes in AH were refractory to TLR stimulation. Compared with healthy controls, both AH monocyte subsets had greater phagocytic capacity, enhanced ability to drive memory T cell proliferation in coculture, and skewed CD4+ T cells to express an increased ratio of IL-17/IFN-γ. Furthermore, liver tissue from AH patients demonstrated an enrichment of monocytes including the intermediate subset compared with controls. These data demonstrate that intermediate monocytes are expanded, functionally activated, induce CD4+ T cell IL-17 expression, and are enriched in the liver of patients with AH.

Modelling Macular Edema: The Effect of IL-6 and IL-6R Blockade on Human Blood-Retinal Barrier Integrity In Vitro.

PURPOSE: Macular edema (ME) is a leading cause of visual loss in a range of retinal diseases and despite the use of antivascular endothelial growth factor (anti-VEGF) agents, its successful treatment remains a major clinical challenge. Based on the indirect clinical evidence that interleukin-6 (IL-6) is a key additional candidate mediator of ME, we interrogated the effect of IL-6 on blood-retinal barrier (BRB) integrity in vitro. METHODS: Human retinal pigment epithelial cell (ARPE-19) and human retinal microvascular endothelial cell (HRMEC) monolayers were used to mimic the outer and inner BRB, respectively. Their paracellular permeability was assessed by measuring the passive permeation of 40 kDa fluorescein isothiocyanate (FITC)-dextran across confluent cells in the presence of IL-6. Transendothelial/epithelial electrical resistance (TEER) then was measured and the distribution of the tight junction protein ZO-1 was assessed by immunofluorescence using confocal microscopy. RESULTS: Treatment with IL-6 for 48 hours significantly increased the diffusion rate of FITC-dextran, decreased TEER, and disrupted the distribution of ZO-1 in ARPE-19 cells, which constitutively express the IL-6 transmembrane receptor, and this was reversed with IL-6R blockade. In contrast, IL-6 did not affect the paracellular permeability, TEER, or ZO-1 distribution in HRMECs. CONCLUSIONS: These in vitro data support the hypothesis that IL-6 reversibly disrupts the integrity of ARPE-19 cells, but it does not affect HRMECs. TRANSLATIONAL RELEVANCE: IL-6 is a candidate therapeutic target in the treatment of outer BRB driven ME.

Re-programming immunosurveillance in persistent non-infectious ocular inflammation.

Ocular function depends on a high level of anatomical integrity. This is threatened by inflammation, which alters the local tissue over short and long time-scales. Uveitis due to autoimmune disease, especially when it involves the retina, leads to persistent changes in how the eye interacts with the immune system. The normal pattern of immune surveillance, which for immune privileged tissues is limited, is re-programmed. Many cell types, that are not usually present in the eye, become detectable. There are changes in the tissue homeostasis and integrity. In both human disease and mouse models, in the most extreme cases, immunopathological findings consistent with development of ectopic lymphoid-like structures and disrupted angiogenesis accompany severely impaired eye function. Understanding how the ocular environment is shaped by persistent inflammation is crucial to developing novel approaches to treatment.

The Bromodomain and Extra-Terminal Protein Inhibitor OTX015 Suppresses T Helper Cell Proliferation and Differentiation.

BACKGROUND: Dynamic epigenetic alterations accompanying CD4+ T helper cell differentiation have been implicated in multiple autoimmune diseases. The bromodomain and extra-terminal (BET) proteins are epigenetic regulators that recognize and bind to acetylated histones in chromatin and are targets for pharmacological inhibition. In this study we tested a new BET inhibitor under clinical development, OTX015, to interrogate its effects on key CD4+ T cell subsets associated with autoimmunity. METHODS: Naïve and memory murine and human CD4+ T cells were isolated and differentiated into populations characterized by the expression of interferon (IFN)-γ and interleukin (IL)-17. Cultured cells were then exposed to varying concentrations of OTX015 in vitro, and its impact on cytokine expression was quantified by flow cytometry. In parallel, the expression of the transcription factors TBX21 and RORC was quantified by PCR. A previously studied BET inhibitor JQ1 was used as a pharmacological control. RESULTS: OTX015 suppressed both murine and human CD4+ T cell proliferation. Its impact on cytokine expression varied in murine and human naïve and memory subsets. OTX015 was similarly effective as JQ1 in the suppression of cytokines and T helper cell proliferation. Higher concentrations of OTX015 also had a greater impact on the viability of murine versus human cells. IL-17 and IFN-γ expression was not altered in murine memory CD4+ T cells, whereas in human memory CD4+ T cells, OTX015 inhibited IL-17, but not IFN-γ. Across all human T cell subsets OTX015 suppressed IL-17 more effectively than IFN-γ. CONCLUSION: Our studies demonstrate that OTX015 has anti-inflammatory effects by suppressing murine and human CD4+ T cell proliferation and subset-dependent proinflammatory cytokine expression, including the selective suppression of IL-17 in human memory CD4+ T cells.

Glucocorticoid-resistant Th17 cells are selectively attenuated by cyclosporine A.

Glucocorticoids remain the cornerstone of treatment for inflammatory conditions, but their utility is limited by a plethora of side effects. One of the key goals of immunotherapy across medical disciplines is to minimize patients' glucocorticoid use. Increasing evidence suggests that variations in the adaptive immune response play a critical role in defining the dose of glucocorticoids required to control an individual's disease, and Th17 cells are strong candidate drivers for nonresponsiveness [also called steroid resistance (SR)]. Here we use gene-expression profiling to further characterize the SR phenotype in T cells and show that Th17 cells generated from both SR and steroid-sensitive individuals exhibit restricted genome-wide responses to glucocorticoids in vitro, and that this is independent of glucocorticoid receptor translocation or isoform expression. In addition, we demonstrate, both in transgenic murine T cells in vitro and in an in vivo murine model of autoimmunity, that Th17 cells are reciprocally sensitive to suppression with the calcineurin inhibitor, cyclosporine A. This result was replicated in human Th17 cells in vitro, which were found to have a conversely large genome-wide shift in response to cyclosporine A. These observations suggest that the clinical efficacy of cyclosporine A in the treatment of SR diseases may be because of its selective attenuation of Th17 cells, and also that novel therapeutics, which target either Th17 cells themselves or the effector memory T-helper cell population from which they are derived, would be strong candidates for drug development in the context of SR inflammation.

Tissue-resident exhausted effector memory CD8+ T cells accumulate in the retina during chronic experimental autoimmune uveoretinitis.

Experimental autoimmune uveoretinitis is a model for noninfectious posterior segment intraocular inflammation in humans. Although this disease is CD4(+) T cell dependent, in the persistent phase of disease CD8(+) T cells accumulate. We show that these are effector memory CD8(+) T cells that differ from their splenic counterparts with respect to surface expression of CD69, CD103, and Ly6C. These retinal effector memory CD8(+) T cells have limited cytotoxic effector function, are impaired in their ability to proliferate in response to Ag-specific stimulation, and upregulate programmed death 1 receptor. Treatment with fingolimod (FTY720) during the late phase of disease revealed that retinal CD8(+) T cells were tissue resident. Despite signs of exhaustion, these cells were functional, as their depletion resulted in an expansion of retinal CD4(+) T cells and CD11b(+) macrophages. These results demonstrate that, during chronic autoimmune inflammation, exhausted CD8(+) T cells become established in the local tissue. They are phenotypically distinct from peripheral CD8(+) T cells and provide local signals within the tissue by expression of inhibitory receptors such as programmed death 1 that limit persistent inflammation.

Effect of chronic FIV infection, and efficacy of marbofloxacin treatment, on Mycoplasma haemofelis infection.

The purpose of this study was to investigate the effect of chronic feline immunodeficiency virus (FIV) infection, and efficacy of marbofloxacin treatment, on Mycoplasma haemofelis infection. Six cats chronically infected with FIV-Glasgow8 (Group X) and six FIV-free cats (Group Y) were infected with M. haemofelis on Day 0 by intravenous blood inoculation. From Day 0 until Day 86 post-infection (pi), blood samples were collected for M. haemofelis and FIV provirus quantitative real-time PCR and haematology. Three of the six cats in each of Groups X and Y were randomly selected to receive marbofloxacin treatment (2 mg/kg PO q24 h) from Day 16 to 43 pi, with the remaining cats being untreated controls with no antibiotic treatment. The M. haemofelis copy numbers and haematological data were compared between Groups X and Y, and between marbofloxacin-treated and control cats using a Mann-Whitney U-test. M. haemofelis infection was associated with development of macrocytic hypochromic anaemia. In some cats, marked variation in M. haemofelis copy number over time (>100,000-fold difference within 48 h in some cats) and/or cycling of copy number was seen. No correlation was found between FIV provirus copy number and M. haemofelis copy number or haematological variables. No significant effect of chronic FIV infection on M. haemofelis copy number kinetics or haematological changes due to M. haemofelis infection was found, other than MCHC (P=0.03). Marbofloxacin treatment was associated with a significant decrease in M. haemofelis copy number (P=0.002), although consistent clearance of infection was not demonstrated. This study reveals the presence of marked fluctuations in M. haemofelis copy number kinetics in vivo and a significant response to marbofloxacin antibiotic treatment.

Effect of chronic feline immunodeficiency infection, and efficacy of marbofloxacin treatment, on 'Candidatus Mycoplasma haemominutum' infection.

The purpose of this study was to investigate the effect of chronic feline immunodeficiency virus (FIV) infection, and efficacy of marbofloxacin treatment, on 'Candidatus Mycoplasma haemominutum' infection. Six cats chronically infected with FIV-Glasgow8 (group A) and six FIV-free cats (group B) were infected with 'Candidatus M. haemominutum' on day 0 by intravenous inoculation of blood. From day 0 to 105 post-infection (pi), blood samples were collected for 'Candidatus M. haemominutum' and FIV provirus quantitative real-time polymerase chain reaction (PCR) and haematological examination. Three of the six cats in each of the groups were randomly selected to receive marbofloxacin treatment (2mg/kg PO SID) from day 49 to day 76 pi, with the remaining cats being untreated controls. Maximum 'Candidatus M. haemominutum' copy number was reached around day 30 pi. No overt cycling or marked variation in copy number was observed. No significant effect of FIV infection on 'Candidatus M. haemominutum' copy number kinetics or anaemia indices was found. No correlation was found between FIV provirus copy number and 'Candidatus M. haemominutum' copy number or haematological variables. Although marbofloxacin treatment was associated with a significant decrease in 'Candidatus M. haemominutum' copy number, the copy number plateaued during treatment, with no negative PCR results. Additionally, after termination of marbofloxacin treatment the copy numbers of the treated cats increased to reach levels similar to those of the untreated cats within 7-10 days. This study documents, for the first time, the infection kinetics and antibiotic responsiveness of 'Candidatus M. haemominutum' infection.