Clinical, hematologic, and immunophenotypic characterization of canine large granular lymphocytosis

Clinical, hematologic, and immunophenotypic data were studied in 25 dogs wi th large granular lymphocyte (LGL) lymphocytosis. Primarily large-breed dog s were affected, with an average age at initial diagnosis of 10 years (rang e 5-14 years). All dogs had persistent (>4 months) LGL lymphocytosis except for three that were euthanized with aggressive disease. Splenomegaly was r eported in 12 of 20 dogs in which splenic size was evaluated. The clinical course was heterogeneous and dogs were divided into four groups based on si milar clinical and hematologic findings: acute leukemia (3/25), persistent lymphocytosis with anemia (12/25), persistent lymphocytosis without anemia (8/25), and reactive lymphocytosis (2/25). Immunophenotypes varied within g roups but were homogeneous among cells from the same patient except in the two dogs classified as reactive LGL lymphocytosis. Analysis of T-cell recep tor (TCR) usage identified three main LGL lineages. TCR alpha beta was expr essed in 15/25 (60%) cases. TCR gamma delta was expressed in 8/25 (32%) cas es, and 2/25 (8%) cases were CD3(-), compatible with NK cells. beta (2) int egrin expression was distinctive. CD11a was consistently expressed, while C D11b was absent. CD11c was expressed only weakly in 16/25 (64%) cases. The leukointegrin alpha (d)beta (2) was highly prevalent on all LGL lineages, b eing expressed in 23/25 (92%) cases. Prominent involvement of the spleen, r elative sparing of bone marrow, an unexpectedly large proportion of gamma d elta T-cell LGLs, and the distinctive beta (2) integrin expression pattern on diverse lineages of LGLs suggest the disease arises from unique populati ons of lymphocytes that preferentially localize in the splenic red pulp.