In the light of the well-known effect of adherence in macrophage activation, attention should be paid to defining the culture conditions of cells isolated by physical methods. As described in Section 2, if activation functions of macrophages are to be studied, it is advantageous to perform these studies on nonadherent macrophages. A variety of non-adherent systems have been established using monocytes isolated by centrifugal elutriation or density gradient centri-fugation. The use of culture dishes made of hydrophobic Teflon (fluorinated ethylene propolyne) film is one of the most common ways to maintain monocytes in a partially adherent state (88, 89). In both adherent and non-adherent systems, monocytes can be maintained in long-term culture, differentiate into culture-derived macrophages, and undergo similar changes in the expression of various cell surface antigens (90). However, some differences have been described between these systems. Non-adherent monocytes respond differently to stimuli than adherent cells. For instance, neither CSF-1 mRNA nor protein is induced by LPS in non-adherent monocytes (91), while LPS treatment of adherent monocytes induces CSF-1 secretion (28). Morphologically, non-adherent monocytes are smaller than adherent cells (90). In addition, a lower activity of some enzymes of intermediary metabolism has been detected in suspension cultures as compared to adherent monocyte cultures (92).
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