CD56 identifies monocytes and not natural killer cells in rhesus macaques

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 examin ed the rot: of CD56 in identifying rhesus NK cells. Methods: The immunophenotype of normal macaque and human NK cells was analy zed by two- and three-color flow cytometry. Flow cytometric cell sorting wa s subsequently used to deplete or purify NK cells; the resulting cell popul ations were then used in standard chromium release assays of NK lytic funct ion. Results: In peripheral blood mononuclear cells of the rhesus macaque, CD56 was expressed primarily on cells with the light scatter and immunophenotypi c profile of monocytes. Flow cytometric depletion of rhesus CD56(+) monocyt ic cells did not diminish functional activity against K562 cells, whereas d epletion of CD8(+) or CD16(+) lymphocytes completely abrogated functional a ctivity. Three-color now cytometric analysis of CD8(+), CD16(+) lymphocytes showed that they expressed other markers (CD2, CD7, TIA-I) associated with NK cells, but notably, not CD56. Conclusions: These studies demonstrate that CD56 is not suitable as a marke r of NK cells in the rhesus macaque. (C) 1999 Wiley-Liss, Inc.