Background: CD56 is a lineage-specific marker of human natural killer (NK) cells. There are conflicts in the literature regarding the role of CD56 as a marker of NK cells in non-human primates. In the present study, we examined the role of CD56 in identifying rhesus NK cells. Methods: The immunophenotype of normal macaque and human NK cells was analyzed by two-and three-color flow cytometry. Flow cytometric cell sorting was subsequently used to deplete or purify NK cells; the resulting cell populations were then used in standard chromium release assays of NK lytic function.
Results:
In peripheral blood mononuclear cells of the rhesus macaque, CD56 was expressed primarily on cells with the light scatter and immunophenotypic profile of monocytes. Flow cytometric depletion of rhesus CD56 ุ monocytic cells did not diminish functional activity against K562 cells, whereas depletion of CD8 ุ or CD16 ุ lymphocytes completely abrogated functional activity. Threecolor flow cytometric analysis of CD8 ุ , CD16 ุ lymphocytes showed that they expressed other markers (CD2, CD7, TIA-1) associated with NK cells, but notably, not CD56. Conclusions: These studies demonstrate that CD56 is not suitable as a marker of NK cells in the rhesus macaque.