Evaluation of CD25-positive cells in relation to the subtypes and prognoses in various lymphoid tumours in dogs.

Interleukin-2 receptor alpha chain (CD25) expression has been reported in human lymphoid tumours and suggested to correlate with the prognosis. In this study, we detected CD25-positive cells in various types of lymphoid tumours in dogs. Immunohistochemical analyses of the tissues from diffuse large B-cell lymphoma (DLBCL) (n = 6), T-zone lymphoma (TZL) (n = 5), and follicular lymphoma (FL) (n = 2) revealed that cells strongly positive for CD25 were observed generally in accordance with lymphoma cell localization. CD25-positive cells were consistently detected in TZL and FL cases; however, the number of CD25-positive cells was variable among DLBCL cases. Furthermore, we evaluated the rate of CD25-positive cells by flow cytometric analysis in 29 dogs with lymphoid malignancies, including high-grade B-cell lymphoma (n = 17), TZL (n = 5), FL (n = 2), cutaneous lymphoma (n=2), and acute lymphoblastic leukaemia (ALL) (n = 3). CD25-positivity in the lymph node cells was significantly higher in dogs with high-grade B-cell lymphoma (mean ± SD, 49.6 ± 31.3%) or TZL (mean ± SD, 80.2 ± 10.0%) than that in healthy dogs (mean ± SD, 9.8 ± 2.8%). In prognostic analysis of 15 cases with high-grade B-cell lymphoma, the progression-free survival was significantly shorter in CD25-high group than that in CD25-low group. The results obtained in this study are useful for subtype differentiation and prognostic analysis of canine lymphomas and future development of molecular-targeted therapy directed at CD25.