Modulation of surface glycoproteins (Mo1, LFA-1, p150,95) by human mononuclear phagocytes

Mo1, LFA-1, and p150,95 are structurally related glycoproteins of the CD11/CD18 complex that are expressed on the membrane of human leukocytes. In the neutrophil, the surface expression of the CD11/CD18 complex is up-modulated (Mo1 greater than p150,95 much greater than LFA-1) by stimulatory factors that include calcium ionophore A23187, phorbol myristate acetate (PMA), and N-L-formyl-L-leucyl-L-phenylalanine (fMLP). Here, in an immunofluorescence analysis, we have examined CD11/CD18 glycoprotein expression by human monocytes, pulmonary alveolar macrophages (PAM, obtained by bronchoalveolar lavage), and breast milk macrophages (BMM) as compared to neutrophils before and after exposure to A23187 (1 microM), fMLP (0.1 microM), or PMA (0.1 microgram/ml) for 15 min at 37 degrees C. Unstimulated monocytes within unfractionated blood mononuclear cells kept at 4 degrees C (n = 13) expressed all three CD11/CD18 glycoproteins, and exposure to A23187 resulted in significant increases in the surface expression of Mo1 (median of 5.7-fold), LFA-1 (median of 2.1-fold), and p150,95 (median of 7.2-fold). Exposure to fMLP- or PMA-stimulated increases of lesser magnitude. CD11/CD18 expression by PAM (n = 9) was barely detectable and was unaffected by exposure to A23187. In contrast, BMM (n = 11) expressed all three CD11/CD18 glycoproteins (with considerable variability among specimens), but no increase was stimulated by A23187. These results demonstrate that monocytes, like neutrophils, have the capacity to respond to activating factors with an increase in CD11/CD18 glycoprotein expression; macrophage differentiation is accompanied by a loss (PAM) or retention (BMM) of CD11/CD18 expression that is unmodulated in response to activation.