Atypical lymphocytes and leukocytes in the peripheral circulation of caged hens

Lymphocytes comprise a family of cells descended from bursa and thymus progenitors whose differentiation is not possible by standard hematology. However, if they are small with a nuclear/cytoplasmic ratio near 1, they are “resting” at least in the microscopic sense. Activation, increases their size, and decreases the nuclear:cytoplasmic (N:C) ratio. Reactive cells are infrequent in healthy animal blood. Their presence indicates an immune response in progress, inflammation, stress, or other pathology. Here the purpose is to describe unusual leukocytes and lymphocytes found in the periphery of commercial hens. Samples of Wright stained blood films obtained from commercial hens housed in modern cages are the data source. Photomicroscopy used an Olympus CX41 light microscope equipped with an Infinity-2 1.4 megapixel charge-coupled device (CCD) Universal Serial Bus (USB) 2.0 camera, at 100× (oil) magnification. Collectively these cells illustrate a continuum between mildly “reactive” to grossly “atypical” states. The description begins with normal resting cells, proceeds to mildly atypical, and concludes with grossly abnormal cells. Bone marrow cells, a source of plasmacytes, are included for comparison. Examples of circulating plasmacytes, large plasmacytoid lymphocytes (LPL), foam cells, and cells expressing properties of more than one lineage are included. The importance of these observations lies in their contribution to cytology, hematology, and immunology. Last, because of the wide use of heterophil:lymphocyte ratios (H:L) as a stress measure they bear directly the welfare issues of caged animals. When cells similar to the types described here are in blood, they indicate stress independent of H:L or other standard measures.