The null T cell in pig blood is not an NK cell.

Up to 50% of the blood lymphocytes in young pigs are thymus-derived, lack all subset-specific markers and appear immunologically unresponsive, with no known functional role. In an examination of their possible role in natural killing, NK activity was found in unpurified mononuclear cells and in preparations of unselected and nylon non-adherent lymphocytes (T cells and Null cells). However, NK activity was abolished by removing the E rosette forming T cells using a rat IgM anti-pig CD2 monoclonal antibody and rabbit complement, but not by control treatments with a non-binding rat IgM monoclonal reagent and complement or with any other reagent alone. Thus the resting Null T cell appears not to play a significant role in natural killing.