The Cytology of Resting and Reactive NK Cells of Chickens

Lymphoid cells are composed of 3 distinct series; those developing in the bursa of Fabricius are B-cells, and those of the thymus are T-cells. The former concern humoral immunity and the latter cell-mediated immunity (CMI). A third lineage, the natural killer cells (NK) develop independently. A study of chicken blood films stained with Wright-Giemsa obtained from a Marek’s disease project provided an opportunity to study NK cells. These lymphoid cells were recognized because of their characteristic cytoplasmic granules. NK size varied from small cells similar in radius (RC) to resting T-cells (RC ~ 3 μm) to larger types (RC ~ 5 μm). Granules also varied in size and number. NKs were often in fields also containing bacteria either free swimming or attached to RBC or other cells. The total white cell count (TWBC) of the study population ranged from leukopenia (very low) to leukemoid reaction (very high) levels (TWBC 5K/μL - 200K/μL; ave. ~50K/μL. NKs comprised 380/45134 (~1.7 %) of all leukocytes. The study population heterophil/lymphocyte ratio (H/L) ave. (~ 0.4) appears to give a false impression of a low stress status. It is concluded as would be the case for plasmacytes or other forms of reactive cells, multiple forms of NK cells appearing in a hemogram indicate inflammation or infection. Therefore, the simple H/L ratio is an inappropriate stress indicator when accompanied by a high TWBC.