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Immune opsonin-independent phagocytosis by pulmonary macrophages
Abstract:
The uptake of albumin-coated latex particles by hamster pulmonary macrophages (PM) in vitro was investigated by using a new technique that combined flow cytometry and fluorescence microscopy to differentiate and quantitate bound vs ingested particles. In the absence of serum, PM avidly bound and ingested particles, whereas phagocytosis by hamster polymorphonuclear leukocytes (PMN) was less marked. In the presence of serum, phagocytosis by PM was slightly depressed, whereas phagocytosis by PMN was stimulated more than 10-fold. The binding of particles to PM in the absence of serum was pH, temperature, and trypsin sensitive and was dependent on the presence of extracellular Ca++ but not Mg++. The ingestion of particles by this immune opsonin-independent pathway was also temperature sensitive but was not affected by either pH or extracellular Ca++. Particle ingestion, but not binding, was inhibited by cytochalasin D and the divalent cation ionophore A23187.
Insights
Hamster pulmonary macrophages (PM) readily bind and ingest albumin-coated particles without serum. Serum enhances phagocytosis by polymorphonuclear leukocytes (PMN) but slightly depresses it in PM.
Area of Science:
- Immunology
- Cell Biology
- Biophysics
Background:
- Pulmonary macrophages (PM) play a crucial role in lung immunity.
- Understanding particle uptake mechanisms is vital for drug delivery and immunology.
- Albumin coating influences particle-cell interactions.
Purpose of the Study:
- To investigate the in vitro uptake of albumin-coated latex particles by hamster pulmonary macrophages (PM).
- To differentiate and quantify bound versus ingested particles using a novel technique.
- To explore the effects of serum, pH, temperature, and cations on particle binding and ingestion.
Main Methods:
- Utilized a combination of flow cytometry and fluorescence microscopy.
- Investigated particle uptake in the presence and absence of serum.
- Assessed the influence of varying pH, temperature, extracellular Ca++, and Mg++ on particle interaction.
- Employed cytochalasin D and ionophore A23187 to probe cellular mechanisms.
Main Results:
- PM avidly bound and ingested particles in serum-free conditions; phagocytosis by polymorphonuclear leukocytes (PMN) was less pronounced.
- Serum addition slightly depressed PM phagocytosis but stimulated PMN phagocytosis over 10-fold.
- Particle binding to PM (serum-free) was sensitive to pH, temperature, trypsin, and Ca++.
- Particle ingestion via the opsonin-independent pathway was temperature-sensitive but unaffected by pH or Ca++.
- Cytochalasin D and A23187 inhibited particle ingestion, but not binding, by PM.
Conclusions:
- Hamster pulmonary macrophages exhibit significant opsonin-independent binding and ingestion of albumin-coated particles.
- Serum differentially modulates phagocytosis by PM and PMN.
- Distinct mechanisms govern particle binding and ingestion by pulmonary macrophages.
- The study provides insights into cellular mechanisms of particle uptake relevant to lung immunity and biomaterial interactions.