Pierre Burtin

Characterization of the nonspecific cross-reacting antigen (NCA) in human monocytes.

Abstract NCA (nonspecific cross-reacting antigen) was revealed by immunofluorescence in all the human adherent monocytes, as well as in the cells of monocyte — macrophage colonies obtained by culture of human bone marrow. By contrast, almost all the monocytes present in PBL before adherence gave a negative reaction with anti-NCA serum. This discrepancy is not due to NCA synthesis during the adherence process, since addition of cycloheximide to the culture medium did not change the reactivity of adherent monocytes with anti-NCA serum. Hence the most logical explantation is an antigenic unmasking during spreading. A similar phenomenon was observed for lysozyme. A few large mononuclear cells were made fluorescent by anti-NCA serum before adherence. These cells were nonadherent and nonphagocytic. Some of them also contained lactoferrin and were classified as precursors of polymorphs. Others did not contain lactoferrin and could be considered immature monocytes.