a-pre-clinical-model-synovitis-using-ex-vivo-human-synovial-tissue

A Pre-Clinical Model of Synovitis Using <em>Ex vivo</em> Human Synovial Tissue with Preserved Function and Architecture

Arthritis is an inflammatory state within joints resulting in cartilage damage, pain, and loss of mobility. Recent advances in arthritis research ...

Ohio State University

Two sibling foxhounds born to a Leishmania seropositive bitch were presented after testing seropositive for Leishmania. Leishmania infantum infection was detected via histopathology, culture, and quantitative polymerase chain reaction (q-PCR). This is the first report of natural infection with Leishmania infantum with the possibility for vertical transmission in North America.

Disseminated Leishmania infantum infection in two sibling foxhounds due to possible vertical transmission.

Dogs are the predominant domestic reservoir for human L. infantum infection. Zoonotic visceral leishmaniasis (ZVL) is an emerging problem in some U.S. dog breeds, with an annual quantitative PCR prevalence of greater than 20% within an at-risk Foxhound population. Although classically Leishmania is transmitted by infected sand flies and phlebotomine sand flies exist in the United States, means of ongoing L. infantum transmission in U.S. dogs is currently unknown. Possibilities include vertical (transplacental/transmammary) and horizontal/venereal transmission. Several reports have indicated that endemic ZVL may be transmitted vertically.

Transplacental transmission of Leishmania infantum as a means for continued disease incidence in North America.

Dogs are the primary reservoir for human visceral leishmaniasis due to Leishmania infantum. Phlebotomine sand flies maintain zoonotic transmission of parasites between dogs and humans. A subset of dogs is infected transplacentally during gestation, but at what stage of the clinical spectrum vertically infected dogs contribute to the infected sand fly pool is unknown.

Leishmania infantum xenodiagnosis from vertically infected dogs reveals significant skin tropism.

Lyme disease is the most widely reported vector-borne disease in the United States. 95% of confirmed human cases are reported in the Northeast and upper Midwest (25,778 total confirmed cases from Northeast and upper Midwest / 27,203 total US confirmed cases). Human cases typically occur in the spring and summer months when an infected nymph Ixodid tick takes a blood meal. Current federal surveillance strategies report data on an annual basis, leading to nearly a year lag in national data reporting. These lags in reporting make it difficult for public health agencies to assess and plan for the current burden of Lyme disease. Implementation of a nowcasting model, using historical data to predict current trends, provides a means for public health agencies to evaluate current Lyme disease burden and make timely priority-based budgeting decisions. The objective of the study was to develop and compare the performance of nowcasting models using free data from Google Trends and Centers of Disease Control and Prevention surveillance reports. We developed two sets of elastic net models for five regions of the United States: 1. Using only monthly proportional hit data from the 21 disease symptoms and tick related terms, and 2. Using monthly proportional hit data from terms identified via Google correlate and the disease symptom and vector terms. Elastic net models using the full-term list were highly accurate (Root Mean Square Error: 0.74, Mean Absolute Error: 0.52, R2: 0.97) for four of the five regions of the United States and improved accuracy 1.33-fold while reducing error 0.5-fold compared to predictions from models using disease symptom and vector terms alone. Many of the terms included and found to be important for model performance were environmentally related. These models can be implemented to help local and state public health agencies accurately monitor Lyme disease burden during times of reporting lag from federal public health reporting agencies.

Inclusion of environmentally themed search terms improves Elastic net regression nowcasts of regional Lyme disease rates.

Lyme disease (LD) due to Borrelia burgdorferi is the most prevalent vector-borne disease in the United States. There is a poor understanding of how immunity contributes to bacterial control, pathology, or both during LD. Dogs in an area of endemicity were screened for B. burgdorferi and  exposure and stratified according to seropositivity, presence of LD symptoms, and doxycycline treatment. Significantly elevated serum interleukin-21 (IL-21) and increased circulating CD3 CD94 lymphocytes with an NK-like CD8 T cell phenotype were predominant in asymptomatic dogs exposed to B. burgdorferi. Both CD94 T cells and CD3 CD94 lymphocytes, corresponding to NK cells, from symptomatic dogs expressed gamma interferon (IFN-γ) at a 3-fold-higher frequency upon stimulation with B. burgdorferi than the same subset among endemic controls. Surface expression of activating receptor NKp46 was reduced on CD94 T cells from LD, compared to cells after doxycycline treatment. A higher frequency of NKp46-expressing CD94 T cells correlated with significantly increased peripheral blood mononuclear cell (PBMC) cytotoxic activity via calcein release assay. PBMCs from dogs with symptomatic LD showed significantly reduced killing ability compared with endemic control PBMCs. An elevated NK-like CD8 T cell response was associated with protection against development of clinical LD, while excess IFN-γ was associated with clinical disease.

Role of NK-Like CD8 T Cells during Asymptomatic Borrelia burgdorferi Infection.

A model of vector-targeted interventions for visceral leishmaniasis.

Resident synovial macrophages (RSMs) are anti-inflammatory, self-renewing macrophages that provide physical immune sequestration of the joint space from the peripheral immune system. Increased permeability of this structure is associated with peripheral immune cells in the synovial fluid (SF). Direct measures of synovial barrier integrity are possible with tissue histology, but after barrier breakdown, if these cells perpetuate or initiate chronic inflammation in SF remains unknown. We sought to identify RSM in human SF as an indirect measure of synovial barrier integrity. To validate findings, we created a novel ex vivo explant model using human synovium. scRNA-seq revealed these SF RSMs upregulated pro-fibrotic and pro-osteoclastic pathways in inflammatory arthritis, but not septic arthritis. Increased frequencies of RSMs in SF was associated with increased sRANKL regardless of underlying pathology. These findings suggest the frequency of RSMs in SF may correlate with synovial barrier damage and in turn, potential damage to joint structures.

Resident synovial macrophages in synovial fluid: Implications for immunoregulation.

Canine leishmaniasis (CanL) and canine monocytic ehrlichiosis (CME) are enzootic in Brazil. Although studies have identified risk factors associated with  seropositivity, very few have combined environmental, social, and dog characteristics, including exposure to other vector-borne pathogens such as , the primary agent of CME in Brazil. In this cross-sectional study, we assessed risk factors associated with  seropositivity in Fortaleza, Brazil, including dog characteristics, exposure to , family socioeconomic status, and environmental factors, using univariate chi-squared tests for independence and multivariable random forest models. Antibodies to  and  were assessed using a chromatographic immunoassay and a rapid ELISA, respectively. In total, 656 dogs were included, with 21.6 % of them being positive for . Large dogs and dogs from families in social stratum 7 were more likely to be exposed to . Random forest classification models with acceptable discrimination (∼0.65) consistently showed that sleeping outside and household social class had the highest variable importance, regardless of the methods used to impute missing explanatory data.  exposure status, along with environmental (backyard type and presence of cats) and dog variables (fur length, deworming frequency, and tick infestation), ranked among the top ten variables in all models. In conclusion, sleeping outdoors and lower social strata were the most relevant risk factors for  seropositivity in dogs from Fortaleza. Large-scale studies are needed to evaluate whether these variables are risk factors for L.  exposure in other areas where CanL is endemic, possibly also incorporating more human and vector data.

Household risk factors associated with canine leishmaniasis in Fortaleza, northeastern Brazil: Environmental, social, dog characteristics, and exposure to canine  spp.

 causes human visceral leishmaniasis and leishmaniosis (CanL) in reservoir host, dogs. As infection progresses to disease in both humans and dogs, there is a shift from controlling type 1 immunity to a regulatory, exhausted T cell phenotype. In endemic areas, the association between tick-borne coinfections (TBCs) and  diagnosis and/or clinical severity has been demonstrated. To identify immune factors correlating with disease progression, we prospectively evaluated a cohort of -infected dogs from 2019 to 2022. The cohort was TBC-negative with asymptomatic leishmaniosis at the time of enrollment. We measured TBC serology, anti- antigen T cell immunity, CanL serological response, parasitemia, and disease severity to probe how nascent TBC perturbs the immune state. At the conclusion, TBC+ dogs with CanL experienced greater increases in anti- antibody reactivity and parasite burden compared to dogs that did not have incident TBC during the study. TBC+ dogs were twice as likely to experience moderate (LeishVet stage 2) or severe/terminal disease (LeishVet stage 3/4). Prolonged exposure to TBC was associated with a shift in  antigen-induced interferon gamma (IFN-γ)/interleukin-10 (IL-10) and enhanced CD8 T cell proliferation. Frequency of proliferating CD8 T cells significantly correlated with parasitemia and antibody reactivity. TBC exacerbated parasite burden and immune exhaustion. These findings highlight the need for combined vector control efforts as prevention programs for dogs in  endemic areas to reduce transmission to humans. Public health education efforts should aim to increase awareness of the connection between TBC and leishmaniosis.

Tick-borne coinfections modulate CD8 T cell response and progressive leishmaniosis.

Dogs play a major role in sustaining transmission of  to people, thus prevention and treatment of canine leishmaniosis (CanL) to reduce transmission represents an unmet public health need. Although advances have been made in understanding how immunopathology correlates to infectiousness as CanL progresses, the immune mechanisms underlying transition between disease stages and terminal decline remain ill-defined. To address this knowledge gap, we generated a comprehensive atlas of peripheral immune cells from control dogs and naturally-infected dogs using single-cell RNA sequencing. The LeishDog Atlas captures the cellular and transcriptional complexity underlying CanL, tracing shifts in immune composition and gene expression across progressive, well-defined disease stages. Notably, we identified distinct myeloid, CD4 and CD8 T cell phenotypes and transcriptional states associated with disease progression. This resource provides a valuable framework for understanding systemic immune dysregulation in CanL, including determinants of T cell exhaustion and myeloid cell activation, and establishes a foundation for comparative, translational, and mechanistic studies of CanL immunopathology and transmissibility.

A single-cell transcriptomic atlas of peripheral blood immune cells spanning progressive canine leishmaniosis.

Visceral leishmaniasis (VL) is a vector-borne disease caused by Leishmania infantum infections in Brazil, and Lutzomyia longipalpis is its main vector. It is not well understood how L. infantum circulates between three hosts of public health importance: dogs, humans, and sand flies. The focus of this study was to determine the detection rate of L. infantum DNA in sand flies and evaluate the relative contribution of the three hosts as sand fly blood sources. Insects were collected using light traps in households with recent history of human VL, close neighbors of VL cases, and households with no recent history of human VL. DNA was extracted from single sand fly guts and L. infantum DNA, and sources of blood were identified by quantitative polymerase chain reaction (qPCR) using specific cytochrome B. Among 248 female sand flies captured, qPCR detected L. infantum DNA in 56% of them. Sand flies captured in households with recent history of human VL or VL endemic neighbors were, respectively, 3.73 (95% CI: 1.64-8.48; P = 4.92e-04) or 6.38 (95% CI: 3.37-12.09; P = 4.62e-10) times more likely to carry L. infantum DNA compared with sand flies captured in houses with no history of VL. Dog blood was most common, but multiple blood sources were detected in individual flies. Our findings reaffirm the role of dogs as L. infantum reservoirs in northeast Brazil. These findings highlight the importance of topical insecticides as measures to prevent canine L. infantum infection and limit the risk of human infection.

Article	Year
Disseminated Leishmania infantum infection in two sibling foxhounds due to possible vertical transmission. The Canadian veterinary journal. La revue vÃ©tÃ©rinaire canadienne\| PubMed ID: 19119370	2008
Transplacental transmission of Leishmania infantum as a means for continued disease incidence in North America. PLoS neglected tropical diseases\| PubMed ID: 21532741	2011
Leishmania infantum xenodiagnosis from vertically infected dogs reveals significant skin tropism. PLoS neglected tropical diseases\| PubMed ID: 34613967	2021
Inclusion of environmentally themed search terms improves Elastic net regression nowcasts of regional Lyme disease rates. PloS one\| PubMed ID: 35271589	2022
Role of NK-Like CD8 T Cells during Asymptomatic Borrelia burgdorferi Infection. Infection and immunity\| PubMed ID: 35416707	2022
A model of vector-targeted interventions for visceral leishmaniasis. The Lancet. Infectious diseases\| PubMed ID: 39134083	2024
Resident synovial macrophages in synovial fluid: Implications for immunoregulation. Clinical immunology (Orlando, Fla.)\| PubMed ID: 39701169	2025
Household risk factors associated with canine leishmaniasis in Fortaleza, northeastern Brazil: Environmental, social, dog characteristics, and exposure to canine spp. One health (Amsterdam, Netherlands)\| PubMed ID: 40687598	2025
Tick-borne coinfections modulate CD8 T cell response and progressive leishmaniosis. Infection and immunity\| PubMed ID: 40741972	2025
A single-cell transcriptomic atlas of peripheral blood immune cells spanning progressive canine leishmaniosis. bioRxiv : the preprint server for biology\| PubMed ID: 41446132	2025
The Presence of Leishmania infantum DNA in Sand Flies Reflects Their Proximity to Human and Canine Visceral Leishmaniasis. The American journal of tropical medicine and hygiene\| PubMed ID: 41662730	2026

Christine A. Petersen

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