Simultaneous expression of CD4 and CD8 antigens by a substantial proportion of resting porcine T lymphocytes

The existence of four subpopulations in resting porcine T lymphocytes is documented. In addition to the two known subpopulations which are typified by a mutually exclusive expression of either the CD8 or the CD4 differentiation antigen, CD4⁻CD8⁺ and CD4⁺CD8⁻ T lymphocytes, respectively, two unusual subpopulations were prominent not only in peripheral blood, but also in lymphoid tissues: CD4⁻CD8⁻ T lymphocytes expressing neither of these antigens and CD4⁺CD8⁺ T lymphocytes coexpressing both antigens. While CD4⁺CD8⁺ lymphoblasts have been found also in other species, resting T lymphocytes with that phenotype are without precedent among all species analyzed to date. This unique composition of the porcine T lymphocyte population has to be taken into consideration when the swine is used as a large animal model in experimental medicine.