Metabolic dysfunction-associated steatohepatitis (MASH) is a global health care burden. Appropriate large animal models mimicking the main MASH characteristics of steatosis, inflammation, and hepatocyte damage alongside progression of fibrosis are imperative for robust preclinical studies, especially in the field of hepatobiliary surgery. The present study aimed to characterize a novel model of steatohepatitis in fumarylacetoacetate hydroxylase-deficient (FAH-/-) pigs. FAH-/- pigs were generated using a CRISPR/Cas9 system. The animals received a choline-deficient, L-amino acid-defined high-fat diet and subtherapeutic doses of nitisinone and were followed for 3 months. Liver biopsies were obtained at baseline and every month during treatment. Steatosis, inflammation, and fibrosis were assessed by conventional histological scoring systems and by an artificial intelligence (AI) model. Serum liver parameters were analyzed every 2 weeks. Steatosis increased significantly throughout the study, with severe steatosis observed as early as 2 months into treatment. The inflammation score was increased in all animals after 3 months of treatment, whereas the AI-based CD45+ cell count showed region-specific trends in the portal and lobular areas. Collagen content and the corresponding fibrosis stage showed an increase over the 3-month period; however, the difference was not significant. Serum liver parameters did not show any relevant elevations during the study. In summary, we successfully developed and characterized a novel model of steatohepatitis in the FAH-/- pig within 3 months. Further studies with prolonged observation time and/or cycling of nitisinone administration are needed to evaluate whether progressive fibrosis and cirrhosis could be achieved with this model.

Diagnosis and classification of ovarian epithelial neoplasms in guinea pigs (Cavia porcellus) are challenging due to inconsistent terminology and few available diagnostic criteria. This study evaluated 23 ovarian epithelial neoplasms in 15 guinea pigs with the objectives of (1) differentiating ovarian surface epithelial (OSE) neoplasms from rete ovarii neoplasms using immunohistochemistry, (2) describing salient histologic features, and (3) classifying neoplasms according to canine, human, and rodent classification schemes. PAX-8 immunohistochemistry separated immunoreactive rete neoplasms from nonreactive OSE neoplasms. OSE neoplasms (n = 12) were well-differentiated and arose directly from the ovarian surface, rather than the primarily cortical location of OSE neoplasms in other species. Focal OSE neoplasms with papillary projections on a fibrous core or tubules within a fibrous stroma were classified as surface papilloma and surface adenoma, respectively. Generalized OSE neoplasms with tubules, papillae, and fibrous stroma were classified as surface borderline tumors. Neoplasms with invasion, 2-4 mitotic figures per 2.37 mm2, and/or peritoneal implantation were classified as surface carcinoma. The only carcinoma with follow-up had resolution of clinical signs and no radiologic evidence of recurrence 6 months after ovariohysterectomy. Rete neoplasms (n = 11) included rete cystadenomas and rete adenomas, and consisted of epithelial cells arranged in papillae and tubules within a rete tubule, with or without cysts, respectively. Further investigation is needed to correlate diagnoses with neoplasms' biologic behavior. We propose using "surface" and "rete" in the diagnosis to denote location, rather than "papillary," "cystic," or "serous," which are variably used in other ovarian neoplasia classification schemes, to standardize terminology.

The histologic diagnosis of some cases of bovine dermatitis can be challenging. We investigated the predominant histologic patterns of dermatitis in cattle, to propose histologic pattern analysis as a diagnostic approach. Sixty-two cases of bovine dermatitis with confirmed etiologic diagnoses were selected in a 20-year retrospective study. The cases included 13 different primary and secondary diseases, ranging from infectious (48/62, 77%) to toxic/irritant-associated diseases (14/62, 23%). The cutaneous lesions were histologically classified into 11 dermatitis patterns, adapted from those described for small animals. Nodular to diffuse dermatitis (22/62, 34%), perivascular dermatitis (14/62, 23%), necrotizing dermatitis (11/62, 18%), and intraepidermal pustular dermatitis (10/62, 16%) were the most common patterns, followed by panniculitis (3/62, 5%); vasculitis (1/62, 2%); and perifolliculitis, folliculitis, or furunculosis (1/62, 2%). The nodular to diffuse, perivascular, necrotizing, and intraepidermal pustular dermatitis patterns included diseases with different etiologies, while the remaining patterns covered a smaller number of distinct cutaneous diseases in each classification. Our results highlighted the histologic analysis as an efficient tool for directing diagnoses, representing a starting point for the application of this technique in large animal dermatology.

The tumor-immune microenvironment (TIME) plays a pivotal role in cancer progression, yet its characterization in veterinary oncology remains limited. Eighty-five soft tissue sarcomas (STSs), comprising fibrosarcomas, leiomyosarcomas, liposarcomas, myxosarcomas, and perivascular wall tumors (PWTs), were immunohistochemically assessed for IBA-1 (total tumor-associated macrophages) and CD204 (M2-like macrophages) expression, scored by image analysis, and correlated with histological parameters. IBA-1 was higher in grade 3 STSs compared with grade 1 (W = 3.40, P = .043) and in PWTs compared with myxosarcomas (W = 6.037, P < .001). CD204 was lower in PWTs compared with fibrosarcomas (W = 5.152, P = .003), leiomyosarcomas (W = 4.394, P = .016), and myxosarcomas (W = 4.812, P = .006). Stratifying by STS type, IBA-1 was higher in grade 2 myxosarcomas compared with grade 1 (Mann U = 4, P = .018). IBA-1 and CD204 were higher in myxosarcomas with necrosis compared with those without (Mann U = 5, P = .026, and Mann U = 0, P = .001, respectively). In PWTs, the mitotic count was higher in cases with higher IBA-1 (Spearman's rho = 0.438, P = .041) and cases with lower CD204 (Spearman's rho = -0.459, P = .035). Considering all STSs, IBA-1 correlated with total tumor-infiltrating lymphocytes (TILs), T-cells, and regulatory T-cells (Tregs). In fibrosarcomas, IBA-1 and CD204 directly correlated with total TILs, T-cells, and Tregs. In myxosarcomas, CD204 correlated with Tregs. In leiomyosarcomas, IBA-1 scores correlated with Tregs and CD204 with T-cells and Tregs. In PWTs, B-cells correlated with IBA-1 and inversely correlated with CD204. These findings suggest the presence of a TIME favoring anti-tumor immunity in PWTs and a pro-tumoral TIME in myxosarcomas, reinforcing the concept that canine STS histotypes elicit distinct immune responses.

ΔNp63 is an isoform of p63 that plays an essential role in the development and growth of some epithelial tissues. In this study, we investigated the expression of ΔNp63 in normal and neoplastic tissues of cats and compared the results with the expression of pan-p63. Immunohistochemistry for ΔNp63 and pan-p63 was performed in normal tissues from 2 adult cats and in 10 cases each of 22 different types of feline neoplasms. In normal tissues, there was nuclear ΔNp63 immunolabeling in basal cells of stratified squamous, transitional, and pseudostratified columnar epithelia; basal cells of sebaceous glands; trophoblasts; and myoepithelial cells. Of the neoplasms, 10/10 apocrine ductal adenomas, 10/10 mammary ductal carcinomas, 10/10 pulmonary adenosquamous carcinomas, 10/10 squamous cell carcinomas, 10/10 trichoblastomas, and 10/10 urothelial carcinomas immunolabeled for ΔNp63. The ΔNp63 immunolabeling was diffuse in almost all neoplastic cells with squamous, basal, and urothelial origins. In the neoplasms with ductal differentiation, only the neoplastic suprabasal myoepithelial cells immunolabeled. Application of pan-p63 to the same set of neoplasms revealed positivity not only in the same neoplasms, but also in several unexpected tumor types (3/10 exocrine pancreatic carcinomas, 3/10 fibrosarcomas, 3/10 pulmonary adenocarcinomas, 2/10 lymphomas, 1/10 cholangiocarcinomas, 1/10 hemangiosarcomas, 1/10 mast cell tumors, and 1/10 meningiomas). Both ΔNp63 and pan-p63 antibodies demonstrated 100% diagnostic sensitivity and negative predictive value for diagnosing feline neoplasms with squamous, basal, and urothelial epithelia or myoepithelial cells. However, ΔNp63 showed higher diagnostic specificity (100% vs. 90.6%), positive predictive value (100% vs. 80%), and overall accuracy (100% vs. 93.1%) compared with pan-p63.

Immunodeficient mice, particularly the NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) strain and other non-obese diabetic (NOD)-derived lines are widely used in biomedical research due to their profound immunosuppression, which enables stable engraftment of human cells and tissues with minimal rejection. Despite their broad utility, these models exhibit unique immunologic and anatomic features and are predisposed to infectious and noninfectious diseases that may confound experimental outcomes and limit translational relevance. This review summarizes current knowledge on spontaneous, infectious, and experimentally induced lesions in NSG and related strains. These mice characteristically display hypoplastic lymphoid organs, including the spleen, thymus, and lymph nodes, due to a near-complete absence of lymphocytes. Spontaneous background lesions include splenic osseous metaplasia, neurodegeneration, pancreatic mastocytosis, cochlear degeneration, intervertebral disk disease, skull hyperostosis, and pancreatic duct cysts, among others. Common spontaneous neoplasms include lymphomas, osteosarcomas, and mammary gland tumors. Due to their immunodeficient status, NSG and NOD-derived mice are also highly susceptible to opportunistic infections, such as Corynebacterium bovis, Chlamydia muridarum, Clostridioides difficile, and mouse kidney parvovirus. In humanized models, engraftment of human immune cells can result in distinctive syndromes, including xenogeneic graft-versus-host disease, post-transplant lymphoproliferative disorders, and chimeric myeloid cell hyperactivation syndrome, which can impact study outcomes and lead to mortality and morbidity. This review is intended as a resource for comparative pathologists to become familiar with these widely used immunodeficient mice, so they can interpret strain-specific lesions and recognize experimental confounders in these mouse models.

Immunodeficient mouse strains are widely used in several fields of biomedical research. Despite that, no standardized system for evaluating immunodeficiency in mice currently exists, and an unbiased comparison of various immunodeficient mouse strains is difficult. The aim of our study was to develop a standardized multi-disciplinary protocol for the morpho-phenotypical assessment of immunodeficient mouse models. We selected 4 immunodeficient strains of mice (Cd40l-/-, Was-/-, Rag1R972Q/R972Q, and Rag1-/-) on a C57BL/6J genetic background and a group of control C57BL/6J wild-type mice. The lymphoid organs were harvested, weighed, and analyzed by histology, immunohistochemistry, and flow cytometry. Hematology and bone marrow cytology were also performed. The main immune cell populations were investigated, including lymphocytes, monocytes/macrophages, neutrophils, and natural killer cells. Relative organ weights were lower in the strains with the highest level of immunodeficiency (Rag1R972Q/R972Q and Rag1-/-). Histology revealed overall lower cellularity in the same strains, particularly in Rag1-/- mice. Tissue spatial distributions of the immune cell populations were confirmed by immunohistochemistry, while flow cytometry allowed for their relative quantification. Likewise, hematology detected moderate lymphopenia in the Rag1R972Q/R972Q mice and more severe lymphopenia in Rag1-/- mice. Our protocol has proven itself effective for the morpho-phenotypical assessment of the immunodeficient mouse models under investigation and was useful in characterizing the type and severity of the defects. The different laboratory techniques were consistent in the characterization and confirmation of immunodeficiency in the different strains, providing different complementary insights.

Injections have been linked to feline sarcomas (feline injection-site sarcoma; FISS) and cutaneous lymphomas (cutaneous lymphoma at injection site; CLIS). Both tumors often exhibit lymphoplasmacytic inflammation ascribed to injected immunogenic material. CLIS is hypothesized to emerge from transformation and clonal expansion of lymphoid cells following persistent immune stimulation with feline leukemia virus (FeLV) reactivation and transformation. To further study whether the lymphocytic infiltrates associated with FISS can represent a suitable niche for the development of CLIS, 34 cases of FISS were examined. Lymphoid cell phenotypes were assessed using CD3 and CD79 immunohistochemistry. For cases with prominent inflammation, FeLV p27 and gp70 immunohistochemistry and PCR for antigen receptor rearrangements were performed. Male domestic shorthair cats predominated. The mean age was 12.2 years (range: 5-17 years). FISS developed in thoracic (8/34, 24%), flank (7/34, 21%), and interscapular (5/34, 15%) regions. Similar proportions of B and T lymphocytes were found in 11/34 (32%) cases; T-cells predominated in 12/34 (35%) cases, and B-cells predominated in 11/34 (32%). At least one FeLV antigen was expressed in lymphoid infiltrates in 10/18 cases (55%), and in neoplastic fibroblasts in 8/18 cases (44%), while both FeLV proteins were expressed in neoplastic cells in 3/18 cases (17%). One cat had clonal T-cell receptor-gamma and was diagnosed with concurrent FISS and CLIS. This case lacked FeLV expression. FeLV amplification from formalin-fixed paraffin-embedded material was unsuccessful. The expression of FeLV p27 and/or gp70 in neoplastic spindle cells and lymphoid infiltrates raises the possibility of FeLV involvement in the tumorigenesis of FISS and CLISs.