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Particle opsonization and lung macrophage cytokine response. In vitro and in vivo analysis
L Kobzik1, S Huang, J D Paulauskis
1Department of Environmental Health, Harvard School of Public Health, Boston, MA.
Abstract:
Inhaled inert particles and organisms cause a spectrum of pulmonary responses, ranging from minimal changes to marked acute inflammation. During ingestion and clearance of such particles, alveolar macrophages (AM) can initiate pulmonary inflammation by production of TNF and neutrophil chemoattractant cytokines. We tested the role of opsonization in determining the AM response to ingestion of inert particles in vitro and in vivo. As measures of AM activation after phagocytosis in vitro, we measured release of TNF and mRNA expression for the platelet-factor 4 family neutrophil chemoattractants, KC and macrophage-inflammatory protein-2 (MIP-2). Using albumin-coated fluorescent latex particle as phagocytic targets, we found a marked release of TNF by AM ingesting particles opsonized with antialbumin IgG, although uptake of similar numbers of unopsonized particles caused little or no release (e.g., 4648 +/- 1147 pg/ml, opsonized beads vs 576 +/- 205 unopsonized, 10:1 particle:cell ratio, n = 4, mean +/- SD). Flow cytometry confirmed equal uptake of the two particle types. Northern analysis of AM mRNA showed marked induction of KC and MIP-2 mRNA after ingestion of opsonized particles only. Instillation of opsonized particles into hamster lungs caused a marked neutrophil influx, although unopsonized particles did not. TNF was elevated in lavage fluid after instillation of opsonized particles, but not after unopsonized beads (92.7 +/- 136 pg/ml opsonized, n = 7 vs 1.3 +/- 3.6 unopsonized, n = 6). KC and MIP-2 mRNA were induced in lavaged cells after instillation of opsonized but not after unopsonized particles or vehicle control. The nature of particle interaction with the AM surface during phagocytosis determines the subsequent AM response. Although many unopsonized inert particles are ingested with minimal AM activation, specific opsonization of pathogens or non-specific adsorption of Ig onto other particles may activate AM and lead to pulmonary inflammation.
Insights
Particle opsonization significantly enhances alveolar macrophage activation, leading to pulmonary inflammation. This study shows that antibody-coated particles trigger a strong inflammatory response, unlike unopsonized particles, highlighting the role of opsonization in lung immunity.
Area of Science:
- Immunology
- Pulmonary Medicine
- Cell Biology
Background:
- Inhaled particles can trigger pulmonary inflammation via alveolar macrophages (AM).
- AM activation involves the production of TNF and neutrophil chemoattractant cytokines.
- The role of particle opsonization in AM activation is not fully understood.
Purpose of the Study:
- To investigate the role of opsonization in determining the AM response to inert particle ingestion.
- To compare the inflammatory effects of opsonized versus unopsonized particles in vitro and in vivo.
Main Methods:
- In vitro studies using albumin-coated latex particles opsonized with anti-albumin IgG.
- Measurement of TNF release and neutrophil chemoattractant mRNA (KC, MIP-2) expression in AM.
- In vivo studies involving particle instillation into hamster lungs and analysis of bronchoalveolar lavage fluid.
Main Results:
- Opsonized particles induced significant TNF release and KC/MIP-2 mRNA expression in AM compared to unopsonized particles.
- Uptake of opsonized and unopsonized particles was similar, indicating activation is dependent on opsonization.
- Instillation of opsonized particles into hamster lungs caused marked neutrophil influx and elevated TNF levels, while unopsonized particles did not.
Conclusions:
- Particle opsonization is a critical factor in triggering alveolar macrophage activation and subsequent pulmonary inflammation.
- The interaction of opsonized particles with AM surface during phagocytosis determines the inflammatory response.
- Specific opsonization or Ig adsorption can activate AM, leading to inflammatory conditions in the lungs.
