Phenotyping of canine lymphoma with monoclonal antibodies directed at cell surface antigens: Classification, morphology, clinical presentation and response to chemotherapy

Detection of Lymphoid Markers (CD3 and PAX5) for Immunophenotyping in Dogs and Cats: Comparison of Stained Cytology Slides and Matched Cell Blocks

Immunolabeling on Romanowsky-stained cytology (RSC) slides can be used, although there is limited evidence of its suitability for phenotyping canine and feline lymphomas. A comparison with matched cell blocks (CB) is missing. Immunolabeling on RSC and CB was compared for lymphoid markers (CD3 and PAX5) in 53 lymphomas and 4 chylous effusions from dogs and cats. The influence of pre-analytical variables (species, time of archive, type of specimens and coverslipping) and the interobserver agreement among the 2 observers was assessed. Fewer CD3+ lymphocytes were identified in RSC, while the PAX5 positivity by RSC and CB had a substantial agreement. Immunodetection of CD3 and the diagnosis of a T-cell population on RSC was more difficult. Lower intensity and higher background were noted in RSC. Immunophenotyping was inconclusive in 54% RSC and 19% CB. The interobserver reproducibility of immunophenotyping on CB was substantial, being higher than in RSC. The immunolabeling performance on the RSC of effusion and feline samples was unsatisfactory. The detection of lymphoid markers, especially membranous antigens in retrospective RSC, is affected by the pre-analytical variables: species, time of the archive, and type of specimens. CB are a more consistent type of sample for immunophenotyping purposes.

Multicenter, randomized, double‐blinded, placebo‐controlled study of rabacfosadine in dogs with lymphoma

Background

Rabacfosadine (RAB, Tanovea‐CA1) is a novel chemotherapy agent conditionally approved for the treatment of lymphoma in dogs.

Hypothesis/Objectives

To determine the efficacy and safety of RAB in dogs with lymphoma.

Animals

One hundred and fifty‐eight client‐owned dogs with naïve or relapsed multicentric lymphoma were prospectively enrolled from January to October 2019.

Methods

Dogs were randomized to receive RAB or placebo at a 3 : 1 ratio. Treatment was given every 21 days for up to 5 treatments. Study endpoints included progression‐free survival (PFS), overall response rate (ORR) at a given visit, best overall response rate (BORR), and percent progression free 1 month after treatment completion. Safety data were also collected.

Results

The median PFS was significantly longer in the RAB group compared to placebo (82 vs 21 days; P < .0001, HR 6.265 [95% CI 3.947‐9.945]). The BORR for RAB‐treated dogs was 73.2% (50.9% complete response [CR], 22.3% partial response [PR]) and 5.6% (0% CR, 5.6% PR) for placebo‐treated dogs (P < .0001). One month after the last treatment, 37 RAB‐treated dogs (33%) were progression free compared with no placebo‐treated dogs (P < .0001). The most common adverse events observed in the RAB group were diarrhea (87.5%), decreased appetite (68.3%), and vomiting (68.3%) and were generally low grade and reversible. Serious adverse events were reported in 24 RAB‐treated (20%) and 5 placebo‐treated dogs (13%).

Conclusions and Clinical Importance

Rabacfosadine demonstrated statistically significant antitumor efficacy in dogs with lymphoma when administered every 21 days for up to 5 treatments as compared to placebo.

Evolution of haematopoietic cell transplantation for canine blood disorders and a platform for solid organ transplantation

Pre-clinical haematopoietic cell transplantation (HCT) studies in canines have proven to be invaluable for establishing HCT as a highly successful clinical option for the treatment of malignant and non-malignant haematological diseases in humans. Additionally, studies in canines have shown that immune tolerance, established following HCT, enabled transplantation of solid organs without the need of lifelong immunosuppression. This progress has been possible due to multiple biological similarities between dog and mankind. In this review, the hurdles that were overcome and the methods that were developed in the dog HCT model which made HCT clinically possible are examined. The results of these studies justify the question whether HCT can be used in the veterinary clinical practice for more wide-spread successful treatment of canine haematologic and non-haematologic disorders and whether it is prudent to do so.

Plasma 25-hydroxyvitamin D and the inflammatory response in canine cancer

Decreased circulating 25-hydroxyvitamin D (25[OH]D) and increased inflammatory marker concentrations have been reported separately in canine cancer. Correlations between the two exist in humans, but little work has examined links in dogs. This study aimed to determine plasma 25(OH)D and inflammatory marker concentrations in healthy dogs and dogs with cancer and to assess correlations in each group. Newly diagnosed dogs with B-cell lymphoma (B-cell, n = 25), T-cell lymphoma (T-cell, n = 9), osteosarcoma (OSA, n = 21), and mast cell tumour (MCT, n = 26) presenting to a tertiary oncology centre, and healthy dogs (n = 25), were enrolled. Plasma samples were analysed for 25(OH)D, C-reactive protein (CRP), haptoglobin (HP), serum amyloid A (SAA), alpha-1-acid glycoprotein (AAG), and 13 chemokines and cytokines. Dogs with B-cell had decreased plasma 25(OH)D (P = .03), and increased plasma CRP, AAG, HP, KC-like and MCP-1 concentrations (P < =.001, .011, <.001, .013 and .009, respectively) compared with healthy dogs. Plasma CRP, HP and SAA concentrations were increased in dogs with OSA compared with healthy dogs (P = .001, .010 and .027, respectively). No differences were noted in dogs with T-cell and MCT. Negative correlations were observed between plasma 25(OH)D concentrations and: AAG concentrations in dogs with T-cell (R_s  = -0.817, P = .007); GM-CSF concentrations (R_s  = -0.569, P = .007) in dogs with OSA; and IL-7 concentrations (R_s  = -0.548, P = .010) in dogs with OSA. Decreased 25(OH)D concentrations and increased concentrations of multiple inflammatory markers were observed in B-cell patients, supporting an association between 25(OH)D and inflammation. The cross-sectional study design meant the timing of changes could not be determined. Prospective cohort studies are warranted.

An Antibody Specific for the Dog Leukocyte Antigen DR (DLA-DR) and Its Novel Methotrexate Conjugate Inhibit the Growth of Canine B Cell Lymphoma

Canine B-cell lymphoma (CBL) is an incurable, spontaneous lymphoid malignancy constituting an accurate animal model for testing novel therapeutic strategies in human medicine. Resources of available species-specific therapeutic monoclonal antibodies (mAbs) targeting CBL are scarce. The aim of the present study was to evaluate the therapeutic potential of mAb B5, specific for the dog leukocyte antigen DR (DLA-DR) and its antibody-drug conjugate with methotrexate (B5-MTX). B5 induced caspase-dependent apoptosis of DLA-DR-expressing canine B cell lymphoma/CLBL1 and CLB70 leukemia lines, but not the GL-1 line not expressing DLA-DR. The cytotoxicity of B5-MTX to sensitive cells was further potentiated by a payload of MTX, but without any substantial off-target effects. The infusion of B5 and B5-MTX in a murine model of disseminated, advanced canine lymphoma, mediated >80% and >90% improvement in survival, respectively, and was well tolerated by the animals. Interestingly, the concentrations of soluble DLA-DR (sDLA-DR) antigens present in the blood serum of tumor-bearing mice were found proportional to the tumor burden. On this basis, sDLA-DR levels were evaluated as a potential biomarker using samples from canine lymphoma patients. In summary, the action of B5 and B5-MTX holds promise for further development as an alternative/complementary option for the diagnosis and treatment of canine lymphoma.

Clinical and histopathological classification of feline intraocular lymphoma

This retrospective study aimed to describe and classify cats with intraocular lymphoma, determine the proportion of cases with presumed solitary ocular lymphoma (PSOL) compared with ocular manifestations of multicentric disease and assess the clinical outcomes of these patients. One hundred seventy-two cases identified through biopsy submissions were reviewed histologically; 163 of these cases were subtyped according to the WHO classification system. Cases were categorized as having PSOL or ocular lymphoma with suspected systemic involvement (SSI) based on submission forms and follow-up data. The majority of cases exhibited concurrent uveitis (75%) and secondary glaucoma (58%). Diffuse large B-cell lymphoma was the most common subtype (n = 86; 53%), followed by peripheral T-cell lymphoma (n = 44; 27%). Other subtypes included anaplastic large T- (n = 8; 5%) and B-cell (n = 4; 2.5%) lymphomas, and 15 cases (9%) were negative for all immunohistochemical markers. In sixty-nine cases (40%), adequate clinical data and sufficient survival data were obtained to distinguish PSOL from SSI. PSOL comprised the majority of cases (64%), while 36% had SSI. When covarying for age at diagnosis, the median survival time was significantly higher (P = 0.003) for cases of PSOL (154 days) versus those with SSI (69 days); hazards ratio of 0.47 for PSOL (95% CI: 0.241-0.937). The subtype of lymphoma did not affect survival time. Cats with PSOL represent a greater proportion of the disease population, and this subset of cats with intraocular lymphoma has a better clinical outcome.

Development of novel monoclonal antibodies to dog leukocyte antigen DR displaying direct and immune-mediated cytotoxicity toward canine lymphoma cell lines

Spontaneous canine lymphoma (CL) has become a promising, nonrodent model for advancing the therapeutic strategies of human hematological malignancies. As new resources for veterinary and comparative studies on CL-associated antigens, we developed 2 novel mouse monoclonal antibodies, denoted B5 and E11, that recognized the canine major histocompatibility Class II DR antigens (dog leukocyte antigen DR). Using flow cytometry and solid phase immunoenzymatic assays, we showed that the antigens recognized by B5 and E11 were strongly expressed in several CL cell lines and the ex vivo canine neoplastic cells of B and mixed B/T immunophenotypes. Additionally, we evaluated a minimal cross-reactivity of B5 and E11 with the human B-cell line, Raji. By the ectopic expression of the hybrid murine/canine I-E/DR dimers in the HEK293 cells, we demonstrated that the epitope of B5 was localized to the invariant DRα chain, whereas the epitope of E11 was collectively formed by the DRα and DRβ chains. Both epitopes were conformational and conserved in all the tested unrelated individuals of different dog breeds. In vitro treatment of 2 CL B-cell lines (CLBL1 and CLB70) with B5 and E11 rapidly induced a direct apoptotic cell death. Similarily, both mouse monoclonal antibodies efficiently killed the above cell lines through the mechanisms of complement-dependent and antibody-mediated cellular phagocytosis. Collectively, our data support the further development of B5 and E11 as novel tools for dog leukocyte antigen DR-targeted, preclinical trials involving CL.

Use of Fine Needle Aspirates and Flow Cytometry for the Diagnosis, Classification, and Immunophenotyping of Canine Lymphomas

Fifty canine lymphomas were classified cytomorphologically using the updated Kiel classification scheme. Aspirates of lymph nodes from dogs with lymphoma were stained using 5 canine-specific antibodies and 3 human-specific antibodies that cross-react with canine lymphocytes. The antibody-stained aspirates were analyzed by flow cytometry. A total of 32 (64%) of the 50 lymphomas were characterized as B-cell origin and 18 (36%) were of T-cell origin. B-cell lymphomas were identified in 12 females and 20 males with a mean age of 8.35 years. T-cell lymphomas were identified in 8 females and 10 males with a mean age of 7.9 years. A minority of the lymphomas were low-grade B-cell and T-cell lymphomas (6/50, 12% and 4/50, 8%, respectively). The most common morphologic types were high-grade centroblastic and unclassifiable plasmacytoid for B- and T-cell lymphomas (18/50, 36% and 7/50, 14%, respectively).

Mechlorethamine, vincristine, melphalan and prednisone (MOMP) for the treatment of relapsed lymphoma in dogs

Eighty-eight dogs with relapsed lymphoma were treated with the MOMP (mechlorethamine, vincristine, melphalan and prednisone) protocol on a 28-day treatment cycle. The overall response rate (ORR) to the MOMP protocol was 51.1% for a median of 56 days (range 7-858 days). Twelve percent of dogs experienced a complete response for a median of 81 days (range 42-274 days) and 38.6% experienced a partial response for a median of 49 days (range 7-858 days). Dogs with T-cell lymphoma had an ORR of 55% for a median of 60 days (range 49-858 days) while those with B-cell lymphoma had an ORR of 57% for a median of 81 days (range 7-274 days) (P = 0.783). The overall survival time for all dogs was 183 days (range 17-974 days). Fifty-four percent of dogs experienced toxicity with the majority classified as grade I. The MOMP protocol seems well-tolerated and is an option for dogs with relapsed lymphoma.

Rapid, effective and user-friendly immunophenotyping of canine lymphoma using a personal flow cytometer

BACKGROUND

Widespread use of flow cytometry for immunophenotyping in clinical veterinary medicine is limited by cost and requirement for considerable laboratory space, staff time, and expertise. The Guava EasyCyte Plus (Guava Technologies, Hayward, CA, US) is the first, personal, bench-top flow cytometer designed to address these limitations.

OBJECTIVE

The aim of this study was to adapt the immunohistochemical protocol used for immunophenotyping of canine lymphoma to the personal flow cytometer for rapid, effective and user-friendly application to the diagnosis and prognosis of canine lymphoma and to demonstrate its practicality for widespread veterinary application. Performance of the personal flow cytometer for immunophenotyping T and B lymphocytes in blood and lymph nodes from normal dogs and dogs with lymphoproliferative disease, was assessed using only two monoclonal antibodies (against CD3 and CD21), and by comparison with analysis using two conventional flow cytometers.

METHODS

26 dogs with lymphoproliferative disease (23 with lymphoma, 3 with lymphocytic leukaemia) were studied along with 15 controls (2 non-lymphoma lymph nodes and 13 non-leukemic bloods. Lymphocytes were immunostained with fluorescent-labeled, monoclonal antibodies against CD3 and CD21. To assess the effectiveness of the personal flow cytometer in discrimination between T and B cell immunophenotypes, T and B cell counts for half the samples (14 blood and 11 lymph node) were also determined using the same method and conventional flow cytometers (FACSCalibur, Cyan Dako). To assess the effectiveness of the personal flow cytometer in discriminating between leukocyte types, lymphocyte differential counts were determined for 21 blood samples and compared with those from automated hematology analyzers (CELL-DYN 3500, n=11 and ADVIA 2120, n=10). Quality and sub-cellular distribution of immunostaining was assessed using fluorescence microscopy.

RESULTS

The protocol for immunophenotyping took 2 to 3 hours to complete from the point of receipt of sample to reporting of immunophenotype. The personal flow cytometer differential lymphocyte counts correlated highly (n=20; r=0.97, p<0.0001) with those of automated haematology analyzers. The personal flow cytometer counts consistently, but mildly, underestimated the percentages of lymphocytes in the samples (mean bias of -5.3%.). The personal flow cytometer immunophenotype counts were indistinguishable from those of conventional flow cytometers for both peripheral blood samples (n=13; r=0.95; p<0.0001; bias of -1.1%) and lymph node aspirates (n=11,r=0.98; p<0.001; bias of 1%). All but one leukemic and one lymphomatous lymph node sample, out of 26 samples of dogs with lymphoproliferative disease analyzed, could be immunophenotyped as either B or T cells.

CONCLUSIONS

We conclude that use of only 2 monoclonal antibodies is sufficient for immunophenotyping most cases of canine lymphoma by flow cytometry and enables rapid immunophenotyping. The personal flow cytometer may be as effectively used for immunophenotyping canine lymphoma as conventional flow cytometers. However, the personal flow cytometer is more accessible and user-friendly, and requires lower sample volumes.

T-cell-derived malignant lymphoma in the boxer breed

The boxer breed of dog is at high risk for a variety of neoplasms including lymphoma. In this observational study, tissue sections from boxer dogs with lymphoma were immunostained for T and B lymphocyte distinction, and the results compared with similar studies carried out on lymphoma tissues from temporally selected cohorts of golden retriever and rottweiler dogs. The frequency of T-cell lymphomas was significantly (P < 0.001 for all comparisons) higher in the boxers than in the rottweilers or golden retrievers. We are unaware of other reports linking immunotype of canine lymphoma with breed; whether other brachycephalic breeds of dogs have a similar preponderance of T-cell lymphoma awaits further study.

Pax5 immunostaining in paraffin-embedded sections of canine non-Hodgkin lymphoma: a novel canine pan pre-B- and B-cell marker

The Pax5 gene encodes the B-cell specific activator protein (BSAP), a member of the highly conserved paired box (PAX)-domain family of transcription factors and a key regulator in the development and differentiation of B-cells. Pax5 serves as a valuable B-cell marker in the classification of human lymphoma patients as it is restricted to lymphomas of B-cell lineage. In dogs, detection of Pax5 protein in lymphoma tissue has not been reported. Therefore, we have investigated the expression and detection of BSAP using a monoclonal anti-Pax5 antibody (anti-BSAP, clone 24) in canine lymphoma tissue samples to evaluate its diagnostic relevance as a B-cell marker. A series of 25 lymph nodes from 23 canine non-Hodgkin lymphoma patients, a reactive canine lymph node, and a normal non-reactive canine lymph node, were evaluated. All B-cell non-Hodgkin lymphomas (15) were found to express Pax5 protein. In addition, there was a strong correlation between Pax5 and CD79a expression. Three CD3 positive and five CD3 and CD79a positive lymphomas were immunophenotypically negative for anti-Pax5, indicating a T-cell lineage. In conclusion, anti-Pax5 antibody may offer an excellent B-cell marker in canine lymphomas.

Determining the Significance of Persistent Lymphocytosis

The authors provide a review of current knowledge of lymphocytosis in nonneoplastic conditions. They conclude that the list of major differentials for persistent nonneoplastic lymphocyte expansion in dogs and cats is short and that most of these conditions are relatively uncommon. Persistent lymphocytosis of small, mature, or reactive lymphocytes is most commonly the result of chronic lymphocytic leukemia or lymphoma. The first step in distinguishing nonneoplastic from neoplastic lymphocytosis is immunophenotyping by flow cytometry to determine the phenotypic diversity of the circulating cells. Clonality testing using the polymerase chain reaction for antigen receptor rearrangements assay is a useful second step in cases in which the phenotype data are equivocal. Once the diagnosis of malignancy has been established, the immunophenotype also provides prognostic information in dogs.

Retrospective Study of 82 Cases of Canine Lymphoma in Austria based on the Working Formulation and Immunophenotyping

In human beings the prevalence of different non-Hodgkin's lymphoma (NHL) subtypes varies according to geographical region. The aim of this study was to classify canine lymphomas in Austria and to compare the results with those of similar studies in other countries. Eighty-two NHLs were classified according to their morphology (based on the Working Formulation) and their immunophenotype (determined with anti-T-cell and anti-B-cell antibodies). Forty-two (51.2%) were of B-cell subtype, 24 (29.3%) of T-cell subtype, and 16 (19.5%) remained unclassified, because of either negative labelling (9/16) or immunoreaction with both antibodies (7/16). Diffuse lymphomas predominated (99%) over follicular lymphomas, while intermediate grade lymphomas (61%) outnumbered high-grade lymphomas (23.2%) and low grade lymphomas (13.4%). The most common subtype was the diffuse large cell lymphoma (40.2%), followed by the large cell immunoblastic lymphoma (13.4%) and the diffuse small lymphocytic lymphoma (13.4%). Follicular large cell lymphoma and small noncleaved cell lymphoma were uncommon (1.2%). Generally, these findings accord with those of similar studies in Western Europe, making the existence of specific risk factors in Austria unlikely.

Lineage differentiation of canine lymphoma/leukemias and aberrant expression of CD molecules

Multiparameter flow cytometry analysis and specific cluster differentiation (CD) molecules were used to determine the expression profiles of B- and T-cell antigens on lymph node preparations from 59 dogs with generalized or multisystemic lymphoma. Lymph node samples from 11 healthy dogs were labeled to validate the specificity of antibodies and to formulate guidelines for interpretation of the results obtained from lymphoma samples. In normal lymph nodes, T-lymphocytes expressing CD3, CD4, or CD8 beta represented 59+/-11%, 43+/-8%, or 16+/-5% of the total cells, whereas B-lymphocytes expressing either CD21 or surface IgM (IgM) represented 37+/-9% or 14+/-5%, respectively. Small lymphocytes could be distinguished from large lymphocytes by forward light scatter. Of the patient samples 29 different breeds were represented with Golden and Labrador retriever being the most common. The lymphoma samples segregated into three groups based on CD antigen expression. Thirty cases predominantly expressed one or more combinations of CD79a, IgM, and CD21 representing a B-cell lineage. Three B-cell cases also expressed the stem cell antigen, CD34. Sixteen cases expressed one or more combinations of CD3, CD4, and CD8 consistent with a T-cell lineage and CD3+CD4+CD8--phenotype was the most common. Thirteen cases showed a mixed expression profile for T- and B-cell antigens and in three cases CD14 was highly expressed. Clinical response was poorest for T-cell lymphomas. Leukemic states occurred in all three phenotypes; but mixed cell cases had the greatest proportion. Dual immunofluorescence staining confirmed co-expression of T-cell (CD3) and B-cell antigens (CD79a or CD21) on neoplastic lymphocytes of six mixed cell cases. In one mixed cell case, dual immunostaining identified lymphocyte populations that stained mutually exclusive for CD79a and CD3. Six mixed cell lymphomas tested by PCR showed clonality for rearranged antigen receptor. Four cases that were CD79a+CD3+ had TCRgamma chain gene rearrangements, whereas two cases that were CD3+CD8+CD21+ had Ig heavy chain rearrangement. One case expressing multiple CD molecules (CD3+CD8+CD21+CD14+) was PCR negative for both Ig and TCRgamma gene rearrangement and could not be classified into a B- or T-cell lineage. We show for the first time co-expression of B- and T-cell markers on lymphoma cells that had specific T- or B-cell gene rearrangements. These findings suggest that aberrant CD molecule expression is not an uncommon finding in canine lymphomas and is a useful diagnostic marker for malignancy.

Distinct B-cell and T-cell lymphoproliferative disease prevalence among dog breeds indicates heritable risk

Immunophenotypes in lymphoproliferative diseases (LPD) are prognostically significant, yet causative factors for these conditions, and specifically those associated with heritable risk, remain elusive. The full spectrum of LPD seen in humans occurs in dogs, but the incidence and lifetime risk of naturally occurring LPD differs among dog breeds. Taking advantage of the limited genetic heterogeneity that exists within dog breeds, we tested the hypothesis that the prevalence of LPD immunophenotypes would differ among different breeds. The sample population included 1,263 dogs representing 87 breeds. Immunophenotype was determined by the presence of clonal rearrangements of immunoglobulin heavy chain or T-cell receptor gamma chain. The probability of observing the number of B-cell or T-cell tumors in a particular breed or breed group was compared with three reference populations. Significance was computed using chi2 test, and logistic regression was used to confirm binomial predictions. The data show that, among 87 breeds tested, 15 showed significant differences from the prevalence of LPD immunophenotypes seen across the dog population as a whole. More significantly, elevated risk for T-cell LPD seems to have arisen ancestrally and is retained in related breed groups, whereas increased risk for B-cell disease may stem from different risk factors, or combinations of risk factors, arising during the process of breed derivation and selection. The data show that domestic dogs provide a unique and valuable resource to define factors that mediate risk as well as genes involved in the initiation of B-cell and T-cell LPD.

Unicentric extranodal lymphoma of the upper eyelid conjunctiva in a dog

A case of conjunctival lymphoma in a 4-year-old Siberian husky is reported. A large red mass protruding from the conjunctiva of the upper eyelid of the right eye was present. Irritation, blepharospasm and epiphora were revealed on initial ophthalmic examination. After anti-inflammatory treatment, surgery was performed. Histologically, the mass consisted of large polygonal cells with a high nucleus to cytoplasm ratio, moderate amounts of slightly eosinophilic cytoplasm, pleomorphic nuclei with vesicular chromatin and prominent multiple nucleoli. Mitotic figures were frequent. Approximately 70% of the neoplastic cells were CD3 positive and CD79alpha negative. On the basis of histologic and immunohistochemical findings, a diagnosis of intermediate-grade, diffuse large-cell lymphoma with T-cell immunophenotype was made. The surgical area healed uneventfully and, although chemotherapy was not received, after 12 months the dog exhibited no recurrence. To the authors' knowledge, this is the first report of unicentric extranodal conjunctival lymphoma in a dog.

Molecular methods to distinguish reactive and neoplastic lymphocyte expansions and their importance in transitional neoplastic states

Although lymphoma and leukemia usually can be diagnosed by routine cytology and histology, some cases present a diagnostic challenge for pathologists and clinicians. Often the dilemma lies in determining whether a population of lymphocytes is reactive or neoplastic. We review currently available methods for analyzing lymphocyte populations by immunophenotyping and by identifying clonally rearranged immunoglobulin and T-cell receptor genes and discuss how these tests can be used to clarify such diagnostic dilemmas. We also describe the detection of chromosomal abnormalities and methods on the horizon, such as gene expression profiling, to identify diagnostically useful oncogenes. Finally, we review the emerging concept of transitional neoplastic states, in which reactive lymphocytes transform to neoplastic lymphocytes in the presence of continued antigenic stimulation, such as that caused by infection with Helicobacter pylori. The existence of transitional neoplastic states underscores the need for an array of molecular diagnostic tools that would improve our ability to characterize lymphocyte populations in human and animal patients and enhance early detection of neoplastic lymphocytes such that eradication of the infectious or inflammatory stimulus could lead to cure.

High-grade canine T-cell lymphoma/leukemia with plasmacytoid morphology: a clinical pathological study of nine cases

The aim of this study is to determine the clinical, morphological, and immunophenotypical presentation of 9 cases of a particular type of canine T-cell lymphoma/leukemia. The morphological presentation was a diffuse infiltration of small, medium-sized, or large blast cells with eccentric nuclei, hyperbasophilic cytoplasm, and a juxtanuclear, pale cytoplasmic area, giving a plasmacytoid appearance and suggesting a B-cell morphology. Surprisingly, all 9 cases were of T-cell phenotype (CD3+). Among the 7 immunophenotyped cases, 4 were CD4-/CD8+, 2 CD8+/CD4+, and 1 CD4+/CD8-. The median Ki-67 index was 65.7%, which placed this lymphoma in the high-grade group. This type of lymphoma/leukemia was found in dogs between 1 and 11 years of age, with a median age of 5.8. The male-female ratio was 0.8 for a reference population of 1.04. The most significant clinical findings were lymphadenopathy either generalized or localized in all cases, a mediastinal mass in 4 cases, bone marrow involvement in 7 cases, hypercalcemia in 4 cases, along with an aggressive clinical course and a poor response to chemotherapy in all cases, with a median disease-free survival time of 3 months.

Proposed criteria for classification of acute myeloid leukemia in dogs and cats

Blood and bone marrow smears from 49 dogs and cats, believed to have myeloproliferative disorders (MPD), were examined by a panel of 10 clinical pathologists to develop proposals for classification of acute myeloid leukemia (AML) in these species. French-American-British (FAB) group and National Cancer Institute (NCI) workshop definitions and criteria developed for classification of AML in humans were adapted. Major modifications entailed revision of definitions of blast cells as applied to the dog and cat, broadening the scope of leukemia classification, and making provisions for differentiating erythremic myelosis and undifferentiated MPD. A consensus cytomorphologic diagnosis was reached in 39 (79.6%) cases comprising 26 of AML, 10 of myelodysplastic syndrome (MDS), and 3 of acute lymphoblastic leukemia (ALL). Diagnostic concordance for these diseases varied from 60 to 81% (mean 73.3 +/- 7.1%) and interobserver agreement ranged from 51.3 to 84.6% (mean 73.1 +/- 9.3%). Various subtypes of AML identified included Ml, M2, M4, M5a, M5b, and M6. Acute undifferentiated leukemia (AUL) was recognized as a specific entity. M3 was not encountered, but this subclass was retained as a diagnostic possibility. The designations M6Er and MDS-Er were introduced where the suffix "Er" indicated preponderance of erythroid component. Chief hematologic abnormalities included circulating blast cells in 98% of the cases, with 36.7% cases having >30% blast cells, and thrombocytopenia and anemia in approximately 86 to 88% of the cases. Bone marrow examination revealed panmyeloid dysplastic changes, particularly variable numbers of megaloblastoid rubriblasts and rubricytes in all AML subtypes and increased numbers of eosinophils in MDS. Cytochemical patterns of neutrophilic markers were evident in most cases of Ml and M2, while monocytic markers were primarily seen in M5a and M5b cases. It is proposed that well-prepared, Romanowsky-stained blood and bone marrow smears should be examined to determine blast cell types and percentages for cytomorphologic diagnosis of AML. Carefully selected areas of stained films presenting adequate cellular details should be used to count a minimum of 200 cells. In cases with borderline diagnosis, at least 500 cells should be counted. The identity of blast cells should be ascertained using appropriate cytochemical markers of neutrophilic, monocytic, and megakaryocytic differentiation. A blast cell count of > 30% in blood and/or bone marrow indicates AML or AUL, while a count of < 30% blasts in bone marrow suggests MDS, chronic myeloid leukemias, or even a leukemoid reaction. Myeloblasts, monoblasts, and megakaryoblasts comprise the blast cell count. The FAB approach with additional criteria should be used to distinguish AUL and various subtypes of AML (Ml to M7 and M6Er) and to differentiate MDS, MDS-ER, chronic myeloid leukemias, and leukemoid reaction. Bone marrow core biopsy and electron microscopy may be required to confirm the specific diagnosis. Immunophenotyping with lineage specific antibodies is in its infancy in veterinary medicine. Development of this technique is encouraged to establish an undisputed identity of blast cells. Validity of the proposed criteria needs to be substantiated in large prospective and retrospective studies. Similarly, clinical relevance of cytomorphologic, cytochemical, and immunophenotypic characterizations of AML in dogs and cats remains to be determined.

Immunophenotyping lymphomas in dogs: a comparison of results from fine needle aspirate and needle biopsy samples

The reliability of utilizing cytologic samples for immunophenotyping canine lymphomas was evaluated by a systematic comparison of results from fine needle aspirate (FNA) to needle biopsy specimens stained by immunochemical methods. The specific reactivity of a selected panel of 12 antibodies to cell surface markers and intermediate filaments was assessed in 11 dogs by comparing cytologic to histologic samples. There was excellent correlation of results between immunostained cytologic and histologic samples. FNA sampling is a simple, noninvasive method for determining the lymphoid phenotype in canine lymphoma. In addition, this technique may be useful as a cytodiagnostic aid in differentiating lymphoid from non-lymphoid tumors and in assessing neoplastic vs. reactive or hyperplastic processes.

Diagnosis of canine lymphoid neoplasia using clonal rearrangements of antigen receptor genes

Although the diagnosis of canine leukemia and lymphoma in advanced stages is usually uncomplicated, some presentations of the disease can be a diagnostic challenge. In certain situations, lymphoma and leukemia can be difficult to distinguish from a benign reactive proliferation of lymphocytes. Because clonality is the hallmark of malignancy, we have developed an assay that uses the polymerase chain reaction to amplify the variable regions of immunoglobulin genes and T-cell receptor genes to detect the presence of a clonal lymphocyte population. The assay detected clonally rearranged antigen receptor genes in 91% of the 77 dogs with lymphoid malignancy. Of the 24 dogs tested, that were either healthy or had clearly defined conditions not related to lymphoid malignancy, a clonally rearranged antigen receptor gene was found in one (a dog with Ehrlichia canis infection). Gene rearrangement was appropriate for the immunophenotype (immunoglobulin gene rearrangement in B-cell leukemias and T-cell receptor gene rearrangement in T-cell leukemias). Dilution analysis showed that the clonal rearrangement could be detected when 0.1-10% of the DNA was derived from neoplastic cells, depending on the source tissue. Potential applications of this assay include the diagnosis of lymphoma or leukemia in biopsy samples, cavity fluids, fine needle aspirates, bone marrow and peripheral blood; the determination of lineage (B or T cell); staging of lymphoma; and detection of residual disease after chemotherapy.

Application of flow cytometric techniques to veterinary clinical hematology

Flow cytometry has emerged as a major new technology in veterinary clinical laboratories. Flow cytometers in current use include stand-alone instruments and cytometers incorporated into hematology analyzers. Flow cytometers offer rapid and quantitative analysis of a variety of cell types based on cell size, molecular complexity, and antigenic composition. Therefore, flow cytometry complements and extends knowledge that can be obtained by light microscopy. Stand-alone instruments are very flexible, however, this flexibility opens the instrument to obtaining invalid or misleading results. The recent development of monoclonal antibodies specific for epitopes on blood cells of food and companion animals has greatly expanded the spectrum of tests with potential clinical application. Tests that appear to have the greatest potential for routine application include reticulocyte and reticulated platelet enumeration, detection of erythrocyte-bound immunoglobulin, immunophenotyping of leukemias and lymphomas, and bone marrow differential cell counting. This report will briefly review the technical aspects of flow cytometry and then focus on techniques with present or potential application to the veterinary clinical laboratory.

Molecular cytogenetic analysis of a novel high-grade canine T-lymphoblastic lymphoma demonstrating co-expression of CD3 and CD79a cell markers

We present the molecular cytogenetic analysis of a novel case of canine lymphoma, in a nine-year-old entire male collie cross retriever dog that presented with an enlarged prescapular lymph node. A diagnosis of high-grade lymphoblastic lymphoma was made by histological evaluation of fixed lymph node biopsy sections, whilst immunohistochemical analyses demonstrated co-expression of B- and T-cell antigens (CD79a and CD3) by 95% of lymphomatous cells. Comparative genomic hybridisation (CGH) analysis detected loss of dog chromosomes 11, 30 and 38 and gain of chromosome 36 within the lymphoma biopsy specimen. These findings correlated with direct cytogenetic analysis of tumour metaphases using whole chromosome paint probes representing each of these four chromosomes. This study represents the first report of the combined application of both direct and indirect cytogenetic techniques for the analysis of recurrent chromosome aberrations in canine cancer.

Immunophenotypic comparison of blood and lymph node from dogs with lymphoma

Peripheral blood and lymph node tissue from 12 dogs with lymphoma was immunophenotyped. Additionally, the bone marrow was immunophenotyped in 6 dogs. The lymphomas were characterized as B-cell in 11 dogs and T-cell in 1 dog. Immunophenotypic patterns in the peripheral blood and bone marrow were variable. The trend in dogs with B-cell lymphoma was normal to increased percentage of IgG-positive cells, decreased percentage of pan-T-positive cells, decreased percentage of CD4-positive cells, and decreased CD4/CD8 ratio. Simultaneous immunophenotyping of lymph node, blood and bone marrow cannot be recommended routinely without further studies to document its value as an independent prognostic indicator. However, it is potentially useful for tumor staging and monitoring remission, especially in lymphoma patients with a leukemic phase.

Canine T-cell lymphomas: a morphological, immunological, and clinical study of 46 new cases

The aim of this study is to report 46 new cases of canine T-cell lymphomas among a series of 140 lymphomas studied by immunophenotyping (incidence 32.8%). According to the updated Kiel classification adapted to the canine species, 13 were classified as low-grade and 33 as high-grade lymphomas. Among the low-grade lymphomas, five were small clear-cell lymphomas, three were pleomorphic small-cell lymphomas, and five mycosis fungoides. Among the high-grade cases, there were 11 pleomorphic mixed-, small-, and large-cell lymphomas, 6 pleomorphic large-cell lymphomas, 11 lymphoblastic lymphomas, and 5 unclassifiable high-grade plasmacytoid lymphomas. The cytohistologic features were highly suggestive of a T-cell phenotype on the basis of cell morphology (irregular nuclei and clear cytoplasms) (30/46 cases), a T-cell zone pattern, and the presence of hyperplastic postcapillary venules (22/46 cases). All 46 cases were CD3+ CD79a-, and among 34 cases investigated for CD4 and CD8 expression, 13 were CD4+CD8-, 13 were CD8+CD4-, and 8 were CD4CD8 double positive or double negative. The pleomorphic mixed lymphomas were mainly CD4+CD8- (6/7) and the lymphoblastic lymphomas were double positive or double negative (6/8). The main clinical, hematologic, and biochemical features were generalized (28/46) or regional lymphadenopathy (16/46), hepatosplenomegaly (15/46), extranodal involvement (11/46), mediastinal mass (9/46), and leukemia (8/46), which were mainly present in cases of lymphoblastic lymphomas and hypercalcemia (16/46).

Prognostic variables in canine multicentric lymphosarcoma

This paper presents the results of a prospective study to investigate the prognostic value of clinical staging, histological grading, immunophenotype, mitotic count and average numbers of argyrophilic nucleolar organiser region counts in dogs with multicentric lymphosarcoma treated with a standard chemotherapy protocol comprising vincristine, cyclophosphamide and prednisolone. Forty-nine dogs were treated according to the study protocol. Univariate and multivariate analysis with regression modelling was used to evaluate the prognostic importance of patient and tumour variables upon tumour response and relapse-free survival. Thirty-seven dogs (76 per cent) achieved a complete remission, seven (14 per cent) a partial remission and five (10 per cent) failed to respond to treatment. None of the variables examined had a statistically significant effect upon tumour response. Tumour immunophenotype was the only parameter found to have a significant influence on patient survival, the hazard ratio for T-cell versus B-cell immunophenotype was 3.99 with 95 per cent confidence interval from 1.399 to 11.372, P = 0.035.

Malignant lymphoma in nasal cavity and paranasal sinuses of a dog

A case of a canine large cell type T-cell lymphoma, with features of high-grade malignancy is described. The tumour was found confined in the nasal cavity and the paranasal sinuses of a crossbred German Shepherd dog. Histological examination revealed the features of a highly malignant large cell lymphoma. Ultrastructurally, the lymphoid tumour cells bore cytoplasmic protrusions that interdigitated tightly. From a panel of tumour markers used, the neoplastic cells were stained only for vimentin. Immunophenotyping of the tumour cells by means of CD3, CD79, kappa-light chains and lambda-light chains detection was undertaken. The tumour stained only for CD3 and was classified as T-cell lymphoma.

Prognostic factors for treated canine malignant lymphoma

The aim of this study was to investigate the prognostic importance of different clinical, immunohistologic and tumor proliferation characteristics in dogs with malignant lymphoma treated with chemotherapy. From 74 dogs with malignant lymphoma at least one enlarged peripheral lymph node was taken for biopsy before chemotherapy following a standardized protocol (vincristine, cyclophosphamide, prednisolone, doxorubicin, and L-asparaginase). The variables evaluated as prognostic factors were age, sex, and tumor stage, as well as histomorphologic grade (Kiel classification, Working Formulation), immunophenotype (using markers for CD3 and CD79a), and cell proliferation (Ki-67, proliferation cell nuclear antigen, mitotic index, and argyrophil nucleolar organizer regions [AgNORs]) in extirpated lymph nodes. All markers were used on routinely formalin-fixed, paraffin-embedded tissues. The AgNORs were assessed qualitatively, based on the AgNOR pattern distribution, and quantitatively using image analysis and routine counting. In both univariate and multivariate survival analyses, AgNORs were a valuable prognostic marker for the treatment of canine malignant lymphomas. Based on the results of the multivariate analysis longer survival time correlated with a B-cell type, a larger mean AgNOR area, a larger total AgNOR area, a shorter distance between two AgNORs, and a smaller AgNOR area to nucleus ratio. Longer disease-free survival time correlated with a smaller number of AgNORs per nucleus, a larger mean AgNOR area, a larger maximal AgNOR area, and a larger total AgNOR area. This study clearly demonstrates the additional benefit of the use of AgNORs in predicting treatment outcome in dogs with malignant lymphoma.

Evaluation of single-agent mitoxantrone as chemotherapy for relapsing canine lymphoma

Many chemotherapeutic regimens will induce remission in dogs with lymphoma, but almost all dogs suffer relapse. Mitoxantrone was selected for evaluation as single-agent chemotherapy for relapsing canine lymphoma based on its use in humans undergoing salvage chemotherapy for non-Hodgkin's lymphoma and its tumoricidal effect against canine lymphoma. Dogs entered into study had multicentric lymphoma, and all had been treated solely with a standard combination chemotherapy protocol. At 1st relapse, all dogs were again staged and underwent lymph node biopsy. Mitoxantrone was administered IV at 6 mg/m2 every 21 days. Dogs were evaluated for lymphadenopathy before each dose of mitoxantrone. Fifteen dogs were entered into study. The average age (+/- SEM) of the dogs studied was 7.7 +/- 0.91 years, and most dogs were large (mean +/- SEM weight, 24.44 +/- 2.15 kg). Twelve dogs (80%) had B-cell lymphoma, and 3 had T-cell lymphoma. Dogs were staged IV (n = 12) or V (n = 3). The median duration of chemotherapy before entry into the study was 98 days. Overall median duration of response after mitoxantrone chemotherapy was 21 days. Complete responses were attained in 7 of 15 dogs (47%) with a median response duration of 84 days. Nine of 15 (60%) dogs attained a complete remission with additional chemotherapy after failing mitoxantrone chemotherapy. Mild toxicities were observed after mitoxantrone administration. No adverse reactions were observed during mitoxantrone infusions. The results of this study demonstrate that mitoxantrone, as a single agent, has limited value for dogs with lymphoma at 1st relapse after conventional multidrug chemotherapy.

Equine malignant lymphomas: morphologic and immunohistochemical classification

Gross lesions, microscopic appearance, and immunophenotyping are reported in a retrospective study of 31 cases of equine malignant lymphoma. Immunohistochemical studies were performed on archived formalin-fixed, paraffin-embedded tissues. Monoclonal antibodies to surface glycoprotein BLA.36 and intracytoplasmic domains of mb-1 and B29 were used to document the presence of B lymphocytes in the equine tumors. Polyclonal antibody to CD3 and monoclonal antibodies to T-lymphocyte markers CD3 and CD5 revealed the presence of variable numbers of T cells within the equine lymphomas. The neoplastic component of the equine lymphomas was determined through morphologic evaluation, immunophenotyping, and the use of proliferation markers Ki-67 and proliferating cell nuclear antigen. Equine malignant lymphomas were composed of a heterogeneous cell population. Most tumors contained B and T lymphocytes. Twenty-four horses had diffuse lymphomas derived from B lymphocytes. Thirteen of these lymphomas contained primarily neoplastic B lymphocytes. Eleven additional cases of diffuse large B-cell lymphoma contained from 40% to 80% nonneoplastic T lymphocytes and were classified as T-cell-rich, large B-cell lymphomas. This is the first description of T-cell-rich, B-cell lymphoma in the horse. Six tumors with a diffuse architecture were derived from T lymphocytes. Four T-cell tumors were large-cell tumors, 1 was a small-cell tumor, and in 1 tumor the size of the cells could not be determined accurately because of autolytic change in the tissues. One diffuse large-cell lymphoma did not react with either B- or T-cell markers.

Cytohistological and immunological classification of canine malignant lymphomas: comparison with human non-Hodgkin's lymphomas

Non-Hodgkin's lymphomas (NHLs) in man are on the increase. They are also common in dogs, which, as close companions of man, may constitute a useful experimental model. However, comparisons cannot be made without a reliable morphological and immunological classification of canine NHL. Canine NHLs (n = 134) were classified on the basis of fine-needle lymph-node aspirates according to the Kiel classification, and 92 were re-classified according to the Working Formulation and the updated Kiel classification, in a histological and immunological study. The immunophenotype was determined (1) in 92 cases by the use of the pan-T anti-CD3 polyclonal antibody and the pan-B anti-mb1 monoclonal antibody on paraffin wax-embedded tissue sections, and (2) in 47 cases by the use of a panel of polyclonal and monoclonal antibodies on fresh preparations and frozen tissue. Cytological analysis showed a predominance of high-grade lymphomas (73.9%) over low-grade lymphomas (26.1%); it also demonstrated forms not reported in other species (small-cell variants, lymphomas with macronucleolated medium-sized cells [MMCs], and polymorphic lymphomas with a centroblastic component). Histological examination revealed the rarity of follicular lymphomas (2.2% of cases), an appearance suggestive of T-cell neoplasia (8.7% of cases), and evidence that some MMC lymphomas originated in the marginal perifollicular zones. Some (26%) of the lymphomas were of the T-cell phenotype: the majority of these consisted of small-cell, low-grade lymphomas and mycosis fungoides, the rest being either high-grade pleomorphic lymphomas (mixed or large-cell) or, rarely, high-grade, small noncleaved-cell, plasmacytoid lymphomas. No lymphoma expressed a double (T and B) phenotype. This study revealed similarities with, but also notable differences from, human NHL. In particular, the MMC lymphomas may constitute an interesting equivalent of human marginal zone B-cell lymphomas.

Growth fractions in canine non-Hodgkin's lymphomas as determined in situ by the expression of the Ki-67 antigen

The proportion of proliferating cells in non-Hodgkin's lymphomas (NHLs) as determined in situ by the expression of the Ki-67 antigen, has prognostic value in human oncology, and is strongly related to the different grades of malignancy. The evaluation of the Ki-67 index in canine NHLs may be useful in assessing the individual variability of the growth fraction in the different sub-types of lymphoma, and also the validity of the classification in terms of grade of malignancy. The growth fraction was evaluated in 92 canine NHLs, previously classified according to the Kiel classification (as adapted to the canine species), by determining the expression of the Ki-67 antigen with the MIB1 antibody on (1) paraffin-wax tissue sections in all 92 cases, and (2) fine-needle aspirates or tumour imprints in 30 cases. The labelling appeared satisfactory in 88% of the cases, with good concordance between the histological and cytological data. A highly significant correlation (P < 0.001) was established between the proportion of Ki-67+ cells and the classification into low-grade (Ki-67 index < 21%) and high-grade malignancy (Ki-67 index > 21% and usually > 29%). In the low-grade lymphoma group, a macronucleolated medium-sized-cell lymphoma not found in man had the lowest proliferation index. In the high-grade malignancy group, the number of Ki-67+ cells seemed to be proportional to cell size, whatever the phenotype, with the rare exceptions of some unclassifiable small-cell Burkitt-type or plasmacytoid lymphomas, which were highly proliferating. The classification of lymphomas into low-grade and high-grade appears to correlate well with their proliferative index. The existence of individual variations, within given categories of canine NHL, suggests that, as in human medicine, prognosis may be assisted by determining the growth fraction at initial diagnosis, and by fine-needle aspiration at relapses.

Studies of canine leucocyte antigens: a significant advance in canine immunology

The Canine Leucocyte Antigen Workshop (CLAW) was set up to produce and circulate monoclonal antibodies directed against cell surface molecules defining specific leucocyte cell types in the dog. The antibodies produced by the workshop have been used in studies of the canine immune system. While many similarities between the dog and other animals have been demonstrated, workshop studies have identified some anomalies in this species: CD4 antigen for example is expressed not only on helper/inducer T-lymphocytes but also at high density on canine neutrophils. Workshop antibodies have been used to investigate lymphocyte populations in the normal dog and in a range of diseases from lymphocytic neoplasms through conditions with an immune-mediated component such as Leishmaniasis to potentially autoimmune disorders such as rheumatoid arthritis and chronic superficial keratitis.

Blood cell markers

Cytochemistry and immunocytochemistry are important adjunctive technologies to the morphologic characterization of blood cells and hematopoietic neoplasms. Although cytochemistry is briefly discussed, the emphasis of this article is on the clinical application of flow cytometry and leukocyte monoclonal antibodies in veterinary medicine. Classification and significance of immunophenotyping in canine and feline lymphomas and immunodeficiencies such as feline immunodeficiency virus and feline leukemia virus are discussed.

Canine lymphoma: immunocytochemical analysis of fine-needle aspiration biopsy

Cytospin preparations of fine-needle aspirates from 21 dogs with peripheral lymphadenopathy (18 with lymphoma and three with lymph node hyperplasia) were studied by combining morphologic and immunocytochemical analysis. Fine-needle aspirates were taken from at least two enlarged lymph nodes, and the diagnosis was based on air-dried smears stained with May-Grünwald Giemsa. Fine-needle aspiration biopsy always provided an adequate quality and quantity of cells to perform morphologic and immunologic studies. Immunophenotyping was performed on cytospin preparations with a panel of eight monoclonal antibodies specific for canine cell surface antigens and one rabbit polyclonal antibody (A452) against human CD3, which cross-reacts with dog antigen. The immunocytochemical study resulted in the diagnosis of 14 B-cell lymphomas (CD21+, CD3-) and three T-cell lymphomas (all CD3+, two CD8+). One lymphoma lacked surface antigens specific for the B- or T-cell lineage and was classified as non-B-non-T lymphoma (CD21-, CD3-, CD4-, CD8-). The monoclonal antibodies CA12.10C12, CA4.1D3, and CA1D6 and the polyclonal antibody A452, used as a group, appeared to be the most useful reagents to suggest lymphoid origin and to discriminate between T-and B-cell phenotype. Cytospin preparations in combination with immunocytochemistry provided a practical, economical, and accurate method for the diagnosis and phenotyping of canine lymphoma.

An original perifollicular zone cell in the canine reactive lymph node: a morphological, phenotypical and aetiological study

In this study of 109 canine reactive lymph nodes, the perifollicular zone (PZ) cell was characterized by cytological, histological, immunocytochemical and electron microscopical techniques. The PZ cell was always found in association with plasma cell hyperplasia. Its main cytological characteristics were medium size, fine chromatin and a large central prominent nucleolus with a small amount of pale cytoplasm. It was located in a clearly recognizable PZ surrounding the follicles; this zone was particularly well developed at the capsular pole of the lymph node. Electron microscopical findings indicated a poorly differentiated cell. Immunolabelling indicated a CD3-, cIg-, Ki-67- immunophenotype, suggesting a resting B cell. These results suggest that the PZ cell belongs either to a post-follicular stage between large immunoblasts and plasma cells or, as is more likely, to a pre-follicular lymphoid subpopulation occurring early in the B-cell differentiation scheme, as with most human marginal zone (MZ) cells. Its high frequency of occurrence in reactive lymph nodes in mammary tumour lymphadenopathies, systemic lupus erythematosus and leishmaniasis, suggests that the PZ cell has a special role in the canine immune response, or perhaps in the arrested maturation of the normal developmental process.

Dermal dendrocytes and T-cells in canine mycosis fungoides. Support for an animal model of human cutaneous T-cell lymphoma

BACKGROUND

An extensive upper dermal network of human Thy-1+/Factor XIIa+ dermal dendrocytes (DD) exists in human mycosis fungoides (MF).

METHODS

Immunophenotyping and morphologic studies on serial frozen and paraffin sections from 15 cases of canine MF were performed to see if a similar network exists in this disease, as has been proposed as an animal model of human MF. Primary antibodies were anti-human Factor XIIIa, Factor XIIIs, anti-canine Thy-1, CD4, CD8, CD18, CD45RA, Class II, MAC387, KP-1, EBM-11, and several other pan-T, pan-B, and pan monocyte markers.

RESULTS

Thy-1+/Factor XIIIa+DD were seen in all cases and confirmed on identical cells by double immunofluorescence. These were seen throughout the upper dermis, similar to DD in human MF. Canine DD expressed the macrophage marker 2A2+, and were Class II+, CD4+, CD8-, CD18+, EBM11-, Factor XIII-, MAC387-, and KP-1. Epidermal and dermal lymphocytes in canine MF were Thy-1-, CD4+, CD8-, CD18+, CD45RA-, EBM11-, MAC387-, Factor XIIIa-, Factor XIIIs- in some cases, whereas others had a predominance of CD8+ lymphocytes.

CONCLUSIONS

Thus, canine MF is immunophenotypically similar to human MF. Additional support for this disease as a model of human MF is demonstrated by the rich network of Thy-1+/Factor XIIIa+ DD in the upper dermis of canine MF similar to human MF.