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Experimental and calculated parameters on particle phagocytosis by alveolar macrophages
Per Camner1, Margot Lundborg, Lena Låstbom
1Division of Inhalation Toxicology, Institute of Environmental Medicine, Karolinska Institutet, SE-171 77 Stockholm, Sweden. Per.Camner@imm.ki.se
Abstract:
Phagocytosis of three types of fluorescein-labeled test particles by rat alveolar macrophages (AM) were studied: spherical silica (3.2 microm), heat-killed Candida albicans (3.8 microm), and heat-killed Cryptococcus neoformans (6.1 microm) opsonized with specific IgG. These particles should attach to scavenger, mannose, and Fc receptors, respectively. Both control AM and AM pretreated for 20 h with interferon-gamma (12.5 or 50 U/ml) were studied. The sum of the number of attached and ingested particles per AM (accumulated attachment) was used as a measure of the attachment process, and the number of ingested particles per AM divided by the accumulated attachment (ingested fraction) was used as a measure of the ingestion process. The average ingestion time (IT), which is also a measure of the ingestion process, was calculated from the experimental data. The ingestion process was independent of the attachment process. IT increased with the time of observation. This is explained by the fact that IT determined from observation times shorter than the whole distribution of IT for a certain particle results in a shorter IT than the real average IT. C. albicans (mannose receptor) had the fastest ingestion process, C. neoformans opsonized with specific IgG (Fc receptor) had ingestion that was nearly as fast, and the silica particles (scavenger receptors) had the slowest ingestion process. Treatment with interferon-gamma markedly impaired the attachment process for all three types of particles (and three types of receptors) but clearly impaired the ingestion process only for silica particles (scavenger receptors).
Insights
Interferon-gamma impairs particle attachment to rat alveolar macrophages (AM) but selectively hinders ingestion of silica particles via scavenger receptors. Different particle types exhibit varied phagocytosis rates.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Alveolar macrophages (AM) are crucial for lung immunity, utilizing various receptors for particle recognition and clearance.
- Phagocytosis involves distinct attachment and ingestion steps mediated by specific cell surface receptors.
Purpose of the Study:
- To investigate the impact of interferon-gamma on the phagocytosis of different particles by rat AM.
- To differentiate the effects of interferon-gamma on particle attachment versus ingestion.
- To compare the phagocytic efficiency of AM for silica, Candida albicans, and Cryptococcus neoformans particles.
Main Methods:
- Rat AM were incubated with fluorescein-labeled silica, Candida albicans, or Cryptococcus neoformans particles.
- AM were either untreated (control) or pretreated with interferon-gamma.
- Attachment and ingestion processes were quantified by measuring accumulated attachment and ingested fraction, and average ingestion time was calculated.
Main Results:
- Interferon-gamma significantly impaired particle attachment to AM across all tested particle types and receptors.
- Ingestion processes were largely independent of attachment, with Candida albicans showing the fastest ingestion, followed by IgG-opsonized Cryptococcus neoformans, and then silica particles.
- Interferon-gamma pretreatment impaired the ingestion of silica particles (scavenger receptors) but not the other particle types.
Conclusions:
- Interferon-gamma differentially affects phagocytosis by rat AM, primarily impairing attachment but selectively hindering the ingestion of scavenger receptor-targeted particles.
- The study highlights the distinct roles of scavenger, mannose, and Fc receptors in particle uptake and the complex regulation of phagocytosis by cytokines.