Superoxide release by peritoneal and bone marrow-derived mouse macrophages. Modulation by adherence and cell activation

Macrophages (Mφ) activated by BCG and other immune stimuli differ from thioglycollate-elicited Mφ (TPM) in releasing O₂^- upon initial contact with a foreign substratum. During adherence and spreading, activated Mφ release ~50% of O₂^- levels triggered by phorbol myristate acetate (PMA). The response requires divalent cations (Ca⁺⁺ or Mg⁺⁺) and is sensitive to lignocaine, a reversible inhibitor of adhesion. These features distinguish this reaction from the response to PMA, which also triggers substantial release of O₂^- from TPM, 60-80% of bacille Calmette-Guerin-activated peritoneal Mφ (BCG-PM) activity. During prolonged cultivation as monolayers, peritoneal and bone marrow derived Mφ (BMDM) progressively lose their ability to release O₂^- in response to PMA and serum-treated zymosan (STZ), although the cells continue to secrete other products and to phagocytose STZ. This loss can be prevented by maintaining peritoneal and BMDM as non-adherent cells in teflon beakers or poly-(2-hydroxyethylmethacrylate) (poly HEMA) coated vessels. High levels of O₂^- activity were observed after cultivating TPM on poly-HEMA (300 nmoles O₂^-/mg/hr after PMA), 10-fold more than adherent controls. BMDM could be induced to release four-fold more O₂^-, > 100 nmoles O₂^-/mg/hr, after cultivation as non-adherent cells in the absence of L cell-conditioned medium. Our results show that heterogeneity in Mφ respiratory burst activity depends on (i) intrinsic differences between populations, (ii) differential responses by activated and non-activated Mφ to selective surface stimuli and (iii) modulation by environmental factors which control adherence and growth.