Characterization of the diffuse mucosal associated lymphoid tissue of feline small intestine

The diagnostic relevance of mesenteric lymph node biopsy in small intestinal lymphoma in cats

BACKGROUND

Regional lymph nodes are frequently sampled in cats with suspected intestinal lymphoma; however, their diagnostic value has not been explored.

OBJECTIVES

To investigate whether histologic and immunohistochemical analysis of mesenteric lymph nodes correlates with the diagnosis of intestinal lymphoma in cats.

ANIMALS

One hundred 2 client-owned cats diagnosed with intestinal lymphoma.

METHODS

Retrospective study. The inclusion criteria required a full-thickness biopsy of the small intestine and concurrent excision of mesenteric lymph nodes. Histologic and immunophenotypic analyses were performed on intestinal biopsies and corresponding lymph nodes. Selected nodal samples diagnosed with reactive lymph nodes underwent clonality testing.

RESULTS

Transmural T-cell lymphomas, encompassing small and large cell types, were predominant (64 cases, 62.7%), with large B-cell lymphomas being more frequently transmural (68.8%) than mucosal (31.2%). Among all lymph nodes examined, 44 (43.1%; 95% CI: 33.9%-52.8%) exhibited neoplastic infiltration. Among cases of small cell lymphoma, 51 out of 72 (70.8%; 95% CI: 59.4%-80.1%) showed no nodal involvement. Clonality results correctly identified 19/30 (63.3%; 95% CI: 45.5%-78.2%) reactive lymph nodes. Concerns were raised regarding clonal identification in the remaining cases and potential misdiagnoses based on phenotypic characteristics.

CONCLUSION AND CLINICAL IMPORTANCE

The study underscores the potential drawbacks of relying solely on mesenteric lymph nodes for diagnosing intestinal lymphomas in cats, particularly small cell subtypes. It emphasizes the importance of full-thickness biopsies for assessing transmural infiltration and recommends caution when utilizing mesenteric lymph nodes for histologic, immunohistochemical and clonality evaluations in mucosal lymphomas. Despite limitations, this research highlights the need for comprehensive diagnostic strategies in cats with intestinal lymphoma.

Immunophenotype investigation in feline intestinal non-B-cell lymphoma

Lymphoma is the most common tumour of domestic cats, developing most frequently in the small intestine. Feline small intestinal lymphoma predominantly demonstrates a T-cell immunophenotype identified by standard immunopositivity for T cells with CD3 or immunopositivity for B cells with CD20. In contrast, a wide spectrum of immunohistochemical antibodies are applied in humans to diagnose the various specific lymphoma subtypes according to the WHO classification. Our aim was to augment our knowledge of immunophenotypes in feline non-B-cell lymphomas forming macroscopic masses in the intestinal tract. We evaluated the combined immunohistochemistry and flow cytometry findings from 15 cases. Neoplastic lymphoid cells were immunopositive for CD3 in 93% (14/15), granzyme B in 87% (13/15), CD5 in 20% (3/15), CD8 in 13% (2/15), CD4 in 7% (1/15) and CD56 in 7% (1/15) of cases. Cytotoxic granules indicating a cytotoxic origin of the neoplastic cells were identified by histopathology only in 13% (2/15) and by cytology in 47% (7/15) of the cases. Without immunohistochemical labelling of the cytotoxic protein granzyme B, the cytotoxic status would have been missed in 46% (6/13) of the cytological and in 85% (11/13) of the histopathological slides. These findings suggest that more complex immunophenotyping may advance our understanding and help prognosticate small intestinal T-cell lymphoma in cats.

Flowcytometric data of intermediate-large cell gastrointestinal lymphoma presenting a gross mass in 32 cats - "let them glow in the flow"

Gastrointestinal lymphoma is the most common form of lymphoma in domestic cats. Aggressive phenotypes are much less common but do bear and unfavorable prognosis. Immunophenotyping by flow cytometry (FCM) is not systematically performed in these patients, because of difficulties in the acquisition of suitable sample material from the gastrointestinal tract. A multimodal diagnostic approach is recommended to improve identification of subtypes targeting patient tailored therapeutic strategies. The aim of this prospective study was to present results of multicolor FCM immunophenotyping in surgically removed gastrointestinal mass and relate them with histopathology using the World Health Organization (WHO) classification and clonality PCR testing. Thirty-two patients were included. Eight cats (25%) had gastric, 23 (72%) had intestinal lymphoma and 1 (3%) had gastric/jejunal lymphoma. Intestinal lymphoma sites were represented by 18 small intestinal, 4 ileocaecal, 1 large intestinal. All gastric lymphomas were diffuse large B-cell lymphoma (DLBCL). Small intestinal lymphomas were 10 enteropathy associated T-cell lymphoma type I (EATL I), 2 enteropathy associated T-cell lymphoma type II (EATL II), 2 peripheral T-cell lymphoma (PTCL), 3 DLBCL and one DLBCL+EATL II. The most common small intestinal FCM T-cell phenotype was CD3+CD21- CD4-CD8-CD18+ CD5-CD79- in 7/10 EATL I and one EATL II. The most frequent FCM B-cell phenotype was CD3-CD21+ CD4-CD8-CD18+ CD5-CD79+ in 13/17 DLBCL and the DLBCL+EATL II. Clonality PCR results were positive in 87.5% (28/32) of all cases. No cross-lineage rearrangement was observed. IHC and FCM results agreed in 87.5% (28/32) of all cases. When all 3 methods were combined, consistent results were seen in 75% (24/32). This is the first demonstration of a multicolor FCM approach set in context to the gold standard histopathology and clonality testing results.

ACVIM consensus statement guidelines on diagnosing and distinguishing low-grade neoplastic from inflammatory lymphocytic chronic enteropathies in cats

BACKGROUND

Lymphoplasmacytic enteritis (LPE) and low-grade intestinal T cell lymphoma (LGITL) are common diseases in older cats, but their diagnosis and differentiation remain challenging.

OBJECTIVES

To summarize the current literature on etiopathogenesis and diagnosis of LPE and LGITL in cats and provide guidance on the differentiation between LPE and LGITL in cats. To provide statements established using evidence-based approaches or where such evidence is lacking, statements based on consensus of experts in the field.

ANIMALS

None.

METHODS

A panel of 6 experts in the field (2 internists, 1 radiologist, 1 anatomic pathologist, 1 clonality expert, 1 oncologist) with the support of a human medical immunologist, was formed to assess and summarize evidence in the peer-reviewed literature and complement it with consensus recommendations.

RESULTS

Despite increasing interest on the topic for clinicians and pathologists, few prospective studies were available, and interpretation of the pertinent literature often was challenging because of the heterogeneity of the cases. Most recommendations by the panel were supported by a moderate or low level of evidence. Several understudied areas were identified, including cellular markers using immunohistochemistry, genomics, and transcriptomic studies.

CONCLUSIONS AND CLINICAL IMPORTANCE

To date, no single diagnostic criterion or known biomarker reliably differentiates inflammatory lesions from neoplastic lymphoproliferations in the intestinal tract of cats and a diagnosis currently is established by integrating all available clinical and diagnostic data. Histopathology remains the mainstay to better differentiate LPE from LGITL in cats with chronic enteropathy.

Predicting Diagnosis of Australian Canine and Feline Urinary Bladder Disease Based on Histologic Features

Anatomic pathology is a vital component of veterinary medicine but as a primarily subjective qualitative or semiquantitative discipline, it is at risk of cognitive biases. Logistic regression is a statistical technique used to explain relationships between data categories and outcomes and is increasingly being applied in medicine for predicting disease probability based on medical and patient variables. Our aims were to evaluate histologic features of canine and feline bladder diseases and explore the utility of logistic regression modeling in identifying associations in veterinary histopathology, then formulate a predictive disease model using urinary bladder as a pilot tissue. The histologic features of 267 canine and 71 feline bladder samples were evaluated, and a logistic regression model was developed to identify associations between the bladder disease diagnosed, and both patient and histologic variables. There were 102 cases of cystitis, 84 neoplasia, 42 urolithiasis and 63 normal bladders. Logistic regression modeling identified six variables that were significantly associated with disease outcome: species, urothelial ulceration, urothelial inflammation, submucosal lymphoid aggregates, neutrophilic submucosal inflammation, and moderate submucosal hemorrhage. This study demonstrated that logistic regression modeling could provide a more objective approach to veterinary histopathology and has opened the door toward predictive disease modeling based on histologic variables.

Results of histopathology, immunohistochemistry, and molecular clonality testing of small intestinal biopsy specimens from clinically healthy client-owned cats

Background

Histopathology, immunohistochemistry, and molecular clonality testing are metrics frequently used to diagnose chronic enteropathy (CE) in cats. However, normal values for these metrics have been based mainly on samples from cats that were relatively young, specific pathogen‐free, or both.

Objectives

To describe results of histopathology, immunohistochemistry, and clonality testing of endoscopically‐derived biopsy specimens of the upper small intestinal tract from a cohort of clinically healthy client‐owned cats.

Animals

Twenty clinically healthy client‐owned cats ≥3 years of age.

Methods

Tissue specimens were collected from the stomach and duodenum and evaluated single blinded by a board‐certified pathologist. In addition, samples were evaluated by routine immunohistochemistry and clonality testing. Cats were followed after the procedure for signs of CE.

Results

Integrated results from histopathology, immunohistochemistry, and clonality testing were interpreted as consistent with small cell lymphoma (SCL; n = 12), emerging SCL (n = 1), lymphocytic enteritis (n = 6), and pseudoclonality (n = 1). On follow‐up, 3 cats eventually developed clinical signs of CE, of which 2 were euthanized 295 and 654 days post‐endoscopy. The remaining 17 cats did not show clinical signs of CE after a median of 709 days (range, 219‐869 days).

Conclusions and Clinical Importance

Intestinal biopsy specimens from clinically healthy client‐owned cats commonly had abnormal findings on histopathology, immunohistochemistry, clonality testing, or some combination of these without apparent clinical relevance. Current diagnostic metrics for diagnosing CE in cats may need modification to be applicable to the general population of cats.

Feline low-grade alimentary lymphoma: an emerging entity and a potential animal model for human disease

BACKGROUND

Low-grade alimentary lymphoma (LGAL) is characterised by the infiltration of neoplastic T-lymphocytes, typically in the small intestine. The incidence of LGAL has increased over the last ten years and it is now the most frequent digestive neoplasia in cats and comprises 60 to 75% of gastrointestinal lymphoma cases. Given that LGAL shares common clinical, paraclinical and ultrasonographic features with inflammatory bowel diseases, establishing a diagnosis is challenging. A review was designed to summarise current knowledge of the pathogenesis, diagnosis, prognosis and treatment of feline LGAL. Electronic searches of PubMed and Science Direct were carried out without date or language restrictions.

RESULTS

A total of 176 peer-reviewed documents were identified and most of which were published in the last twenty years. 130 studies were found from the veterinary literature and 46 from the human medicine literature. Heterogeneity of study designs and outcome measures made meta-analysis inappropriate. The pathophysiology of feline LGAL still needs to be elucidated, not least the putative roles of infectious agents, environmental factors as well as genetic events. The most common therapeutic strategy is combination treatment with prednisolone and chlorambucil, and prolonged remission can often be achieved. Developments in immunohistochemical analysis and clonality testing have improved the confidence of clinicians in obtaining a correct diagnosis between LGAL and IBD. The condition shares similarities with some diseases in humans, especially human indolent T-cell lymphoproliferative disorder of the gastrointestinal tract.

CONCLUSIONS

The pathophysiology of feline LGAL still needs to be elucidated and prospective studies as well as standardisation of therapeutic strategies are needed. A combination of conventional histopathology and immunohistochemistry remains the current gold-standard test, but clinicians should be cautious about reclassifying cats previously diagnosed with IBD to lymphoma on the basis of clonality testing. Importantly, feline LGAL could be considered to be a potential animal model for indolent digestive T-cell lymphoproliferative disorder, a rare condition in human medicine.

Feline alimentary lymphoma: 1. Classification, risk factors, clinical signs and non-invasive diagnostics

PRACTICAL RELEVANCE

Alimentary lymphoma (AL) occurs commonly in cats and exists as distinct subtypes that differ in their clinical course, response to treatment and prognosis. Accurate diagnosis is important to guide appropriate treatment.

CLINICAL CHALLENGES

Differentiation of low-grade alimentary lymphoma from lymphoplasmacytic enteritis can be challenging, especially where endoscopic intestinal biopsies, which sample only the mucosa and submucosa, are used. The major differentials for intermediate- and high-grade alimentary lymphoma are other neoplastic and non-neoplastic intestinal mass lesions. The diagnosis of large granular lymphocyte lymphoma requires vigilance as it may be missed with routine diagnostics.

PATIENT GROUP

AL affects predominantly middle- to old-aged domestic crossbred cats (median age 10-13 years).

EVIDENCE BASE

The evidence supporting this review is grade II, III and IV, derived from prospective studies, retrospective case series, reviews, extrapolation from other species, pathophysiological justification and the combined clinical experience of those working in the field.

Characterization of the Gastric Immune Response in Cheetahs (Acinonyx jubatus) With Helicobacter-Associated Gastritis

Captive cheetahs have an unusually severe progressive gastritis that is not present in wild cheetahs infected with the same strains of Helicobacter. This gastritis, when severe, has florid lymphocyte and plasma cell infiltrates in the epithelium and lamina propria with gland destruction, parietal cell loss, and, in some cases, lymphoid follicles. The local gastric immune response was characterized by immunohistochemistry in 21 cheetahs with varying degrees of gastritis. The character of the response was similar among types of gastritis except that cheetahs with severe gastritis had increased numbers (up to 70%) of lamina proprial CD79a+CD21– B cells. CD3+CD4+ T cells were present in the lamina propria, and CD3+CD8α+ T cells were within the glandular epithelium. Lymphoid aggregates had follicular differentiation with a central core of CD79a+/CD45R+ B cells and with an outer zone of CD3+ T cells that expressed both CD4 and CD8 antigens. MHC II antigens were diffusely expressed throughout the glandular and superficial epithelium. No cheetah had evidence of autoantibodies against the gastric mucosa when gastric samples from 30 cheetahs with different degrees of gastritis were incubated with autologous and heterologous serum. These findings indicate that T-cell distribution in cheetahs is qualitatively similar to that in other species infected with Helicobacter but that large numbers of lamina propria activated B cells and plasma cells did distinguish cheetahs with severe gastritis. Further research is needed to determine whether alterations in the Th1:Th2 balance are the cause of this more plasmacytic response in some cheetahs.

Feline Gastrointestinal Lymphoma

Gastrointestinal lymphomas were identified in 120 cats between 1995 and 2006. Lymphomas were classified according to the World Health Organization (WHO) scheme. Cats with mucosal T-cell lymphoma ( n = 84) predominated and had a median survival of 29 months. Mucosal T-cell lymphoma matched WHO enteropathy-associated T-cell lymphoma (EATCL) type II. Epitheliotropic T-cell infiltrates were present in 62% of cats and occurred as clusters or diffuse infiltrates of small to intermediate-sized T cells in villous and/or crypt epithelium. Similar lymphocytes infiltrated the lamina propria in distinctive patterns. Cats with transmural T-cell lymphoma ( n = 19) had a median survival of 1.5 months. Transmural T-cell lymphoma matched WHO EATCL type I. Epitheliotropic T-cell infiltrates were present in 58% of cats. Large lymphocytes ( n = 11), mostly with cytoplasmic granules (LGL–granzyme B+) ( n = 9) predominated. Transmural extension across the muscularis propria characterized the lesion. Both mucosal and transmural T-cell lymphomas were largely confined to the small intestine, and molecular clonality analysis revealed clonal or oligoclonal rearrangements of T-cell receptor-γ in 90% of cats. Cats with B-cell lymphoma ( n = 19) had a median survival of 3.5 months. B-cell lymphomas occurred as transmural lesions in stomach, jejunum, and ileo–cecal–colic junction. The majority were diffuse, large B-cell lymphomas of centroblastic type. In conclusion, T-cell lymphomas characterized by distinctive mucosal architecture, CD3 expression, and clonal expansion predominated in the feline gastrointestinal tract.

Diagnostic algorithm to differentiate lymphoma from inflammation in feline small intestinal biopsy samples

Differentiating between inflammatory bowel disease (IBD) and small intestinal lymphoma in cats is often difficult, especially when only endoscopic biopsy specimens are available for evaluation. However, a correct diagnosis is imperative for proper treatment and prognosis. A retrospective study was performed using surgical and endoscopic intestinal biopsy specimens from 63 cats with a history of chronic diarrhea or vomiting or weight loss. A diagnosis of lymphoma or inflammation was based on microscopic examination of hematoxylin and eosin (HE)-stained sections alone, HE-stained sections plus results of immunohistochemical labeling (IHC) for CD3e and CD79a, and HE staining, immunophenotyping, and polymerase chain reaction (PCR) results for B and/or T cell clonality. In addition, various histomorphologic parameters were evaluated for significant differences between lymphoma and IBD using Fisher's exact test. The sensitivity and specificity of each parameter in the diagnosis of lymphoma were also determined. Results of Bayesian statistical analysis demonstrated that combining histologic evaluation of small intestinal biopsy specimens with immunophenotyping and analysis of clonality of lymphoid infiltrates results in more accurate differentiation of neoplastic versus inflammatory lymphocytes. Important histologic features that differentiated intestinal lymphoma from IBD included lymphoid infiltration of the intestinal wall beyond the mucosa, epitheliotropism (especially intraepithelial nests and plaques), heterogeneity, and nuclear size of lymphocytes. Based on the results of this study, a stepwise diagnostic algorithm that first uses histologic assessment, followed by immunophenotyping and then PCR to determine clonality of the lymphocytes, was developed to more accurately differentiate between intestinal lymphoma and IBD.

Polyomavirus infection in a free-ranging California sea lion (Zalophus californianus) with intestinal T-cell lymphoma

An adult female California sea lion (Zalophus californianus) that stranded in central California was found to have a small glossal polypoid mass on gross necropsy. Histologically, the mass was consistent with a fibropapilloma, and intranuclear inclusions were found within endothelial cells lining small arterioles within the mass. Electron microscopy revealed 40-nm virions within endothelial intranuclear inclusions. Rolling circle amplification was used to obtain a partial viral genomic sequence. Sequence analysis identified the virus as a novel polyomavirus, tentatively named California sea lion polyomavirus 1. In addition, the sea lion had a severely thickened small intestine and swollen pale kidneys on gross examination. Severe renal amyloidosis with chronic interstitial nephritis was diagnosed histologically as well as T-cell intestinal lymphoma, which was confirmed via immunophenotyping and molecular clonality. The relationship, if any, between polyomavirus infection and the other disease processes in this sea lion is not known, but it is considered unlikely that the polyomavirus induced the lymphoma.

Histopathological standards for the diagnosis of gastrointestinal inflammation in endoscopic biopsy samples from the dog and cat: a report from the World Small Animal Veterinary Association Gastrointestinal Standardization Group

The characterization of inflammatory change in endoscopic biopsy samples of the gastrointestinal mucosa is an increasingly important component in the diagnosis and management of canine and feline gastrointestinal disease. Interpretation has hitherto been limited by the lack of standard criteria that define morphological and inflammatory features, and the absence of such standardization has made it difficult, if not impossible, to compare results of retrospective or prospective studies. The World Small Animal Veterinary Association (WSAVA) Gastrointestinal Standardization Group was established, in part, to develop endoscopic and microscopical standards in small animal gastroenterology. This monograph presents a standardized pictorial and textual template of the major histopathological changes that occur in inflammatory disease of the canine and feline gastric body, gastric antrum, duodenum and colon. Additionally, a series of standard histopathological reporting forms is proposed, to encourage evaluation of biopsy samples in a systematic fashion. The Standardization Group believes that the international acceptance of these standard templates will advance the study of gastrointestinal disease in individual small companion animals as well as investigations that compare populations of animals.

Food Allergy in Dogs and Cats: A Review

Food allergy (FA) is defined as "all immune-mediated reactions following food intake," in contrast with food intolerance (FI), which is non-immune-mediated. Impairment of the mucosal barrier and loss of oral tolerance are risk factors for the development of FA. Type I, III, and IV hypersensitivity reactions are the most likely immunologic mechanisms. Food allergens are (glyco-)proteins with a molecular weight from 10-70 kDa and are resistant to treatment with heat, acid, and proteases. The exact prevalence of FA in dogs and cats remains unknown. There is no breed, sex or age predilection, although some breeds are commonly affected. Before the onset of clinical signs, the animals have been fed the offending food components for at least two years, although some animals are less than a year old. FA is a non-seasonal disease with skin and/or gastrointestinal disorders. Pruritus is the main complaint and is mostly corticoid-resistant. In 20-30% of the cases, dogs and cats have concurrent allergic diseases (atopy/flea-allergic dermatitis). A reliable diagnosis can only be made with dietary elimination-challenge trials. Provocation testing is necessary for the identification of the causative food component(s). Therapy of FA consists of avoiding the offending food component(s).

Feline large granular lymphocyte (LGL) lymphoma with secondary leukemia: primary intestinal origin with predominance of a CD3/CD8(alpha)(alpha) phenotype

Clinicopathologic and immunophenotypic characteristics of large granular lymphocyte (LGL) neoplasia in 21 cats were examined. All cats were domestic short (19) or long hair (2) with a mean age of 9.3 years at diagnosis. Increased peripheral blood LGL counts were present in 18/21 cats. Neutrophilia (12/21 cats) and increased serum liver enzymes (7/12), total and direct bilirubin (7/13), BUN (5/14), and creatinine (2/14) were observed. Cats usually presented with advanced disease and none survived longer than 84 days (mean 18.8 days) postdiagnosis. Cytologically, LGLs had a mature (6/21), immature (13/21), or mixed (2/21) morphology. Necropsy lesions consisted of neoplastic lymphoid infiltrates in the jejunum, ileum, and duodenum in decreasing order of frequency. In the small intestine, mucosal ulceration (9/13) and epitheliotropism of neoplastic cells (9/13) were common. Neoplastic infiltrates were also present in the mesenteric lymph nodes (13/13), liver (12/13), spleen (8/13), kidneys (5/7), and bone marrow (5/7). A T cell phenotype (CD3epsilon+) characterized LGL neoplasia in 19/21 cases. A CD8alphaalpha+ cytotoxic/suppressor phenotype was present in 12/19 T cell tumors, 2 had a CD4+CD8alphaalpha phenotype, 3 had a CD4-CD8- phenotype, and 2 were CD4+ helper T cells. CD8beta chain expression was not detected in any instance. In two cats, a B or T cell origin could not be established. CD103 was expressed by 11 of 19 (58%) of the lymphomas tested. The immunophenotypic features shared by neoplastic LGLs in the cat and feline intestinal intraepithelial lymphocytes (IELs) support a small intestinal IEL origin for feline LGL lymphoma.

Mucosal defence along the gastrointestinal tract of cats and dogs

Diseases that are associated with infections or allergic reactions in the gastrointestinal and respiratory tracts are major causes of morbidity in both cats and dogs. Future strategies for the control of these conditions require a greater understanding of the cellular and molecular mechanisms involved in the induction and regulation of responses at the mucosal surfaces. Historically, the majority of the fundamental studies have been carried out in rodents or with tissues obtained from man, but the expanding range of reagents available for the study of farm and companion animals provides opportunities for study in a wider range of animals including cats and dogs. To date, these studies have tended to be focussed on characterising the cellular distributions in healthy animals and in groups of cats and dogs identified as having an increased risk of mucosal disturbance. Where species comparisons of mucosal immune systems have been made, the results have tended to be divided between monogastric and ruminant animals. It is then not surprising that the mucosal immune systems of both cats and dogs bear greatest similarity to that documented for man and pigs. For example, IgA is the dominant immunoglobulin in mucosal secretions of cats and dogs and oral tolerance can be induced following the introduction of novel antigens into the diet. Also like several other species, cats become transiently hypersensitive to the newly introduced dietary antigen prior to the establishment of tolerance. In contrast, there are a number of potentially important differences. In particular, there are significant differences between cats and dogs in the expression MHC class II molecules on gut epithelial cells. Similarly, it has been reported that cats have elevated numbers of intraepithelial lymphocytes (IEL) and that a proportion of these express surface IgM. It remains to be determined if these differences reflect the way in which the animals are maintained and if they may have greater biological significance.

Upregulation of ICOS on CD43+ CD4+ murine small intestinal intraepithelial lymphocytes during acute reovirus infection

Murine intestinal intraepithelial lymphocytes (IELs) can be classified according to expression of a CD43 glycoform recognized by the S7 monoclonal antibody. In this study, we examined the response of S7+ and S7- IELs in mice during acute reovirus serotype 3 (Dearing strain) infection, which was confirmed by virus-specific real-time PCR. In vivo proliferation increased significantly for both S7- and S7+ IELs on day 4 post-infection as determined by BrdU incorporation; however, expression of the inducible costimulatory (ICOS) molecule, which peaked on day 7 post-infection, was upregulated on S7+ CD4+ T cells, most of which were CD4+8- IELs. In vitro ICOS stimulation by syngeneic peritoneal macrophages induced IFN-gamma secretion from IELs from day 7 infected mice, and was suppressed by treatment with anti-ICOS mAb. Additionally, IFN-gamma mRNA increased in CD4+ IELs on day 6 post-infection. These findings indicate that S7- and S7+ IELs are differentially mobilized during the immune response to reovirus infection; that the regulated expression of ICOS is associated with S7+ IELs; and that stimulation of IELs through ICOS enhances IFN-gamma synthesis during infection.

Methodology for isolation and phenotypic characterization of feline small intestinal leukocytes

Critical assessment of intestinal immune responses requires the ability to characterize leukocytes from different anatomic locations as leukocytes from inductive sites such as Peyer's patches and lymphoid follicles vary significantly from their effector counterparts, intraepithelial lymphocytes (IEL) and lamina propria lymphocytes (LPL). This study describes (1) methods developed to isolate specific intestinal leukocyte populations with high yield and purity, (2) difficulties encountered in establishing a panel of monoclonal antibodies to assess phenotype, and (3) the phenotypic characterization of effector and inductive sites in the feline small intestine. We found that the phenotypic distribution of feline intestinal leukocytes was similar to that found in other species such as humans, macaques and mice. The majority of IEL were CD5(+) T-cells with less than 7% B-cells. CD8(+) T-cells comprised approximately 60% of the IEL with roughly half displaying CD8alphaalpha homodimers. Approximately 10% of IEL were CD4(+) T-cells. In the LPL, CD4(+) T-cells predominated at 42%, with 33% CD8(+) T-cells and 10% B-cells. As would be expected, B-cells predominated in Peyer's patches with 40% B-cells, 28% CD4(+) T-cells and 20% CD8(+) T-cells. Increased MHCII expression was found in the Peyer's patches as compared to the IEL and LPL. B7.1 expression was significantly higher in mucosal leukocyte populations as compared to organized lymphoid tissue in the periphery with expression detected on 65% of IEL and 53% of LPL. Plasma cells were found in all regions of small intestine examined with greater numbers in lamina propria and Peyer's patches. Lymphoblasts were only identified in inductive tissue. In general, no differences were found between the phenotype of mucosal leukocyte populations from specific pathogen free or random source cats. However, the percentage of CD4(+) CD25(+) T-cells was significantly greater in both IEL and LPL from random source animals. This study provides techniques and a baseline from which future studies of the feline intestinal immune system can be conducted.

Characterization of feline T cell receptor gamma (TCRG) variable region genes for the molecular diagnosis of feline intestinal T cell lymphoma

A diagnosis of intestinal lymphoma is currently made on the basis of clinical and morphologic criteria. This can prove problematic for many reasons that include inadequate sample size, the coexistence of lymphoma and inflammation, and the inability to assess architectural integrity of all tissue compartments in biopsy specimens obtained endoscopically. The detection of a clonal population of cells in a lymphoproliferative lesion represents an important criterion for the diagnosis of neoplasia, but this has not been assessed in feline intestinal lymphoma. T cell receptor gamma (TCRG) gene rearrangement analysis using polymerase chain reaction (PCR) is a methodology that can be used to detect clonality in T cell populations. The basis of this assay depends on the assessment of the junctional diversity that results from rearrangement of TCRG V (variable) and J (joining) gene segments. Feline TCRG transcripts from normal small intestine and spleen were obtained using a rapid amplification of cDNA ends (5'RACE) method. Limited diversity of TCRG V and J gene segments was observed. The high degree of sequence homology in the TCRG V and J gene segments was exploited to develop a PCR test for the assessment of TCRG V--J junctional diversity and hence clonality determination of T cell populations in cats. Molecular clonality determination was applied to feline intestinal lymphoplasmacytic inflammatory bowel disease (IBD) (9 cats), and transmural and mucosal T cell lymphoma (28 cats). Clonal rearrangement of the TCRG V--J junction was detected in 22 of 28 intestinal T cell lymphomas, and oligoclonality was detected in 3 intestinal T cell lymphomas. This contrasted with the detection of polyclonal rearrangement in normal intestinal tissues (3 cats) and in lymphoplasmacytic IBD (9 cats). It is proposed that assessment of TCRG V--J junctional diversity for the detection of clonality represents an important adjunctive tool for the diagnosis of T cell lymphoma in the cat.

Chronic lymphocytic leukemia in dogs and cats: the veterinary perspective

Chronic lymphocytic leukemia (CLL) in dogs and cats shares many similarities with its human counterpart but also has significant differences. In marked contrast to people, CLL in dogs and cats is primarily a T-lymphocyte proliferation. Cytotoxic T-cell proliferations with granular lymphocyte morphology predominate in dogs, and T helper cell proliferations seem to be most common in cats with CLL. Immunophenotyping and assessment of clonality by molecular genetic analysis are newer adjunctive tools in veterinary medicine that are useful in the characterization and diagnosis of CLL in dogs and cats. The clinical presentation, typical hematologic findings, diagnosis, course of disease, prognosis, and therapy of CLL in dogs and cats are discussed.

Feline gastrointestinal lymphoma

Gastrointestinal lymphoma is a common cause of anorexia and weight loss in older cats, with or without vomiting or diarrhea. Most cats are feline leukemia virus-negative and feline immunodeficiency virus-negative. Low-grade gastrointestinal lymphoma may be more common than previously thought, and these cats respond better to chemotherapy agents than cats with high-grade lymphoma. The most significant prognostic indicator is initial response to chemotherapy, with cats that survive the initial induction period generally achieving long-term remission. Thus far, investigations into molecular markers and immunophenotyping have failed to identify useful prognostic indicators.

Feline epitheliotropic intestinal malignant lymphoma: 10 cases (1997-2000)

The clinical, histopathologic, and immunohistochemical features of 10 cats with epitheliotropic intestinal malignant lymphoma (EIL) are described. Intestinal biopsy samples were reviewed by 3 pathologists to confirm the diagnosis of EIL. These samples (n = 10) were compared to the intestinal biopsies of normal cats (n = 11), cats with inflammatory bowel disease (IBD; n = 7), and cats with non-EIL (n = 9) for quantification and immunophenotyping of intraepithelial lymphocytes. Immunophenotypic studies were performed with CD3 and CD79a antibody stains to assess for T- and B-cell immunoreactivity, respectively. EIL biopsies had markedly more intraepithelial lymphocytes than normal intestine (NRL) and samples from cats with IBD. However, no marked difference was observed in the number of intraepithelial lymphocytes in cats with non-EIL compared to cats with EIL. Regardless of the histologic diagnosis, the intraepithelial lymphocytes in all cats were small- to intermediate-sized T cells. Clinical findings and imaging studies in the cats identified minimal or nonspecific findings in affected cats. Most cats fit the typical profile of cats with IBD or alimentary malignant lymphoma. Nine of 10 cats with EIL were treated with prednisone with or without additional chemotherapy. Four cats were refractory to chemotherapy and were euthanized within 3.5 months. The remaining 5 cats had long-term survival times of 11 months or greater. The median survival time was 11 months. Additional studies are warranted to better characterize EIL and its relationship to IBD in cats and non-EIL and to identify optimal treatment strategies for this disease.

Characterization of a feline homologue of the alphaE integrin subunit (CD103) reveals high specificity for intra-epithelial lymphocytes

The characteristics of a feline homologue of the alphaE integrin (CD103), defined by two murine monoclonal antibodies, Fe7.1B8 (IgG1) and Fe7.2D8 (IgG1), are described. These antibodies recognized 75% of intra-epithelial (range 59-88%) and 40% of lamina proprial (range 28-46%) T cells of the intestinal mucosal tissue of the small intestine in contrast with approximately 2% of peripheral blood lymphocytes. Both antibodies immunoprecipitated a 180 kDa protein from biotinylated feline intra-epithelial mucosal leukocytes consistent with the alphaE integrin subunit in conjunction with a 120 kDa protein consistent with the beta7 subunit. The nucleotide sequence of feline alphaE integrin, generated from molecular cloning of the feline alphaE encoding cDNA, is also reported. This feline molecule shares 72% sequence homology with human and 69% homology with murine and rat counterparts. Homology includes the presence of an X (extra) domain, that appears unique to alphaE molecules as described for human, rat and mouse, as well as areas of homology common to other alpha integrins. Of note is a typical I (inserted) domain, the presence of seven repeat regions, and highly conserved sequences in the cytoplasmic tail. Transfection studies demonstrated that both antibodies recognized an extracellular component which encompassed the X and I domains of the cloned alphaE integrin subunit. These studies demonstrate that the pattern of tissue distribution, biochemical characteristics, and cDNA sequence of the feline alphaE integrin subunit are largely similar to that described for other species.