DIFFERENTIAL EXPRESSION OF NATURAL-KILLER-CELL MARKERS - HUMAN VERSUSBABOON

The use of baboons as a model for the study of allo- and xenotransplan tation has become increasingly important, but there are few studies on the basic immunological responses in baboons that might be relevant f or a rejection reaction. In present study, the cell-surface phenotype, cytokine-induced activation and growth, and cytotoxicity of baboon an d human natural killer (NR) and lymphokine-activated killer (LAK) cell s were compared. A panel of murine monoclonal antibodies specific for human cell-surface markers expressed on lymphocytes was used to compar e relevant baboon and human peripheral blood lymphocytes (PBL), Baboon PBL were 52.1+/-2.9% CD8(+), 18.5+/-2.2% CD16(+), 3.0+/-0.5% CD25(+), and 5.5+/-1.8% CD69(+). The corresponding proportions in humans were 23.8+/-7.1%, 12.8+/-3.2%, 4.5+/-1.0%, and 2.3+/-1.1%. In contrast to h uman PBL, less than 1% of baboon lymphocytes expressed CD56, CD57, and CD122 (interleukin [IL]-2R beta). Baboon lymphocytes showed NK cytoto xic activity against the human K562 and CEM cell lines, which was comp arable to human NK activity. Depletion of baboon CD16(+) or CD8(+) cel ls led to dramatic decreases in NK cytotoxicity, and removal of both s ubsets completely abrogated NK activity. Incubation of baboon lymphocy tes with human recombinant IL-2 for 1 week led to the appearance of CD 56(+) cells (11.3+/-2.8%). Most of the baboon CD56(+) cells induced in culture were in S and G2 phases of cell cycle. Both baboon and human IL-2-activated lymphocytes were highly cytotoxic against the human LAK -sensitive cell line Daudi. Depletion of baboon CD8(+) but not CD56(+) cells significantly decreased LAK activity. These studies revealed di fferences in the NK system of humans and baboons that should be taken into consideration when analyzing immune responses to allo- and xenotr ansplantation in baboons.