IMMUNOHISTHOCHEMICAL DETECTION OF CD25+ LYMPHOCYTES IN FELINE INJECTION-SITE SARCOMA

CD25 (IL-2Ra) is the α-subunit of the membrane-bound interleukin-2 receptor (IL-2R), which is mainly expressed by regulatory T cells (Tregs). Tregs play a pivotal role in the homeostasis of the immune system and in the modulation of the immune response (1,2). Two type of Tregs are known: natural Treg and adaptive Treg. Normally these cells regulate immune system activity and prevent autoimmunity. Imbalanced function or number of these cells, either enhanced or decreased, might lead to tumor development and autoimmunity, respectively (1,2,3,4). In the present study we hypothesized the presence of CD25+ cells among tumor infiltrating lymphocytes (TILs) that are normally associated with feline injection-site sarcoma (FISS), a type of tumor considered a good model to study a link between inflammation and neoplasia. To this end the CD25 protein expression levels were analyzed by immunohistochemistry in eighteen cases of FISS. 4 μm sections were immunostained by avidin-biotin technique for CD25 (Thermo Scientific, mouse monoclonal antibody). Staining was evaluated semi-quantitatively for percentage of positivity (10 fields at 40X) and the expression was considered as follows: percentage <20% = weak positivity; 21-50% = moderate positivity; >50% = strong positivity. All the cases studied (18/18) had TILs positive for CD25. The immunolabeling appeared as distinct membrane staining or as diffuse cytoplasmic expression. 4 cases weakly expressed CD25 protein, 5 cases had moderate expression and 9 cases strongly expressed CD25. The medium expression percentage for all the 18 cases was of 55%. The present study identified large proportions of CD25+ cells among tumor-infiltrating lymphocytes in FISS. The exact function and molecular mechanism by which CD25 is associated with carcinogenesis is still unclear. As observed in experimental animal model, CD25+ lymphocytes inhibit Th1 and CD8+ immune response and consequently they could represent a permissive and stimulatory factor for tumor development. The knowledge on their induction, activation and function opens the possibility for their selective in vivo manipulation as an attractive immunotherapeutc approach in a tumor such as FISS. 1)Sakaguchi S. Naturally arising CD4+ regulatory T cells for immunologic self-tolerance and negative control of immune responses. Annu Rev Immunol 2004; 22:531–562. 2) McHugh R.S., Whitters M.J., Piccirillo C.A., et al. CD4(+)CD25(+) immunoregulatory T cells: gene expression analysis reveals a functional role for the glucocorticoidinduced TNF receptor. Immunity 2002; 16:311–323. 3)Dieckmann D., Bruett C.H., Ploettner H., Lutz M.B., Schuler G. Human CD4(+)CD25(+) regulatory, contact dependent T cells induce interleukin 10-producing, contactindependent type 1-like regulatory T cells. J Exp Med 2002; 196:247–253. 4)Nishikawa H., Sakaguchi S. Regulatory T cells in cancer immunotherapy. Curr Opin Immunol 2014; 27:1–7 VETERINARY ONCOLOGY CD25, sarcoma, immunohistochemistry