HUMAN BLOOD MONOCYTES, BUT NOT ALVEOLAR MACROPHAGES, REVEAL INCREASEDCD11B CD18 EXPRESSION AND ADHESION PROPERTIES UPON RECEPTOR-DEPENDENTACTIVATION/

The beta(2) integrin receptor CD11b/CD18 mediates adhesion to the endo thelial lining as well as to extracellular matrix components, The pres ent study was undertaken to investigate peripheral human blood monocyt es (BMs) and alveolar macrophages (AMs) with respect to quantitative l evels of CD11b/CD18 and adhesion properties in relation to the state o f activation. BMs and Ams were recruited from healthy subjects. Quanti tative analysis of the surface expression of CD11b/CD18 by flow cytome tric technique and adhesion properties to albumin-coated surfaces were performed both on resting and N-formyl-methionyl-leucyl-phenylalanine (fMLP)-activated cells, Receptor independent stimuli (phorbol-12-myri state-13-acetate (PMA) and ionomycin) were used in additional experime nts, Intracellular stored CD11b/CD18 was evaluated by flow cytometry a nd immunofluorescence microscopy. The surface expression of CD11b/CD18 on resting BMs increased fivefold (p<0.01) upon fMLP activation, On r esting AMs, the surface expression of CD11b/CD18 was significantly hig her (p<0.01) compared to resting BMs but did not increase further upon activation with fMLP, PMA or ionomycin, In contrast to BMs, no eviden ce for an additional intracellular pool of CD11b/CD18 was found in AMs , The adherence of resting BMs did not significantly differ from the a dherence of resting AMs, After fMLP activation, the adherence of BMs, but not AMs, increased significantly (p<0.05). Our results indicate th at in vivo differentiation of human blood monocytes into alveolar macr ophages implies reduced responsiveness to fMLP in terms of CD11b/CD18 upregulation and adhesion properties, and that the Lack of upregulatio n of CD11b/CD18 on alveolar macrophages presumably depends on the abse nce of an additional intracellular pool.