Lymphoma in Psittacine Birds: A Histological and Immunohistochemical Assessment

Abstract

In psittacine birds, round cell neoplasms that originate from lymphocytes, plasma cells, histiocytes, or mast cells are sporadic and poorly described. The lack of morphological and immunohistochemical diagnostic criteria or grading schemes make specific diagnoses and prognoses challenging. We assessed cases of psittacine birds diagnosed with round cell neoplasia from 3 North American veterinary diagnostic laboratories to describe the diagnostic features of these tumors. For all cases, demographic data, anatomic distribution, histological features, and immunoreactivity for T (CD3) and B (Pax5 and MUM-1) cell markers were assessed using tissue microarrays and whole slide mounts. Thirty-eight psittacine birds representing 14 species were included. Tumors were mainly infiltrative and multicentric, were composed of homogenous sheets of round to polygonal cells, and commonly presented with a high mitotic count (average 21 mitoses per high-power field). Based on Pax5 immunoreactivity, B-cell lymphoma was most common (19/38 [50%]), and was significantly associated with involvement of the gastrointestinal and urogenital systems. Of the 38 cases, 6 (16%) were consistent with T-cell lymphoma, 3 (8%) with plasma cell tumor, and 3 (8%) were double-reactive for both B- and T-lymphocyte markers. This is the first study to describe morphologic and immunohistochemical features of round cell neoplasia in a large number of psittacine birds, and provides benchmark data for future studies aimed at elucidating the diagnosis and prognosis of these neoplasms. These data also provide useful information about reactivity of commercially available antibodies as lymphocyte markers in tissues of multiple psittacine species.

Keywords: Psittaciformes; avian; histopathology; immunohistochemistry; immunophenotype; lymphoma; round cell neoplasia.

Figure 1.

Percentage of cells that are immunoreactive for CD3, Pax5, and MUM-1 in 6 immunophenotypes of round cell neoplasms assessed in 38 psittacine birds. Mean ± standard error. Three cases were excluded due to autolysis.

Figures 2–6.

Round cell neoplasms, psittacine birds. Columns “a,” “b,” and “c” show immunohistochemistry for CD3 (alkaline phosphatase chromogen, membranous labeling), Pax5 (alkaline phosphatase chromogen, nuclear labeling), and MUM-1 (NovaRed chromogen, nuclear and some cytoplasmic labeling), respectively. Figure 2. B-cell lymphoma, intestine, lineolated parakeet, case 1. There are rare cells with immunoreactivity for CD3 (a), while the majority shows strong immunoreactivity for Pax5 (b), and many cells are immunoreactive for MUM-1 (c). Figure 3. T-cell lymphoma, skin, green-cheeked conure, case 22. The majority of the neoplastic cells are immunoreactive for CD3 (a) and rare scattered cells are immunoreactive for Pax5 (b) and MUM-1 (c). Figure 4. T-cell lymphoma with MUM-1 reactivity, spleen, budgerigar, case 25. The majority of the cells are immunoreactive for CD3 (a), with only a few small cell aggregates immunoreactive for Pax5 (b). The majority of the cells are strongly immunoreactive for MUM-1 (c). Figure 5. Plasma cell tumor, spleen, Indian ring-necked parakeet, case 27. Scattered cells are immunoreactive for CD3 (a) and Pax5 (b), but the majority of the cells have mild immunoreactivity for MUM-1 (c). Figure 6. Double-reactive lymphoma, intestine, Amazon parrot, case 29. The majority of the cells show strong immunoreactivity for CD3 (a), light immunoreactivity for Pax5 (b), and strong to mild immunoreactivity for MUM-1(c).

Figure 7.

Infiltrative B-cell lymphoma, intestine, cockatiel, case 12. Neoplastic cells expand and efface the intestinal mucosa, submucosa, and muscularis. This neoplasm has a high proportion of Pax5 immunoreactive cells. Hematoxylin and eosin (HE). Inset: the neoplastic population transmurally effaces the intestine and extends to the adjacent pancreas (asterisk) and mesentery. HE. Figure 8. Infiltrative T-cell lymphoma with MUM-1 reactivity, liver, cockatiel, case 23. (a) There is marked anisocytosis and anisokaryosis and frequent multinucleate cells. HE. (b) Nuclear immunoreactivity for MUM-1. (c) Cytoplasmic to membranous immunoreactivity for CD3.