Phagocytosis by Human Monocytes

What type of cell are monocytes closely related to?

Tissue macrophages of the reticuloendothelial system.

What major functions do monocytes/macrophages perform?

Defense against microbes, antigen processing, removal of damaged RBCs, tissue repair, bone remodeling.

What is required for many monocyte functions?

Particle ingestion (phagocytosis).

What technique was used to isolate human monocytes?

Albumin flotation (Bennett & Cohn method).

What purity range did monocyte preparations achieve?

55–99.5%, usually with neutrophils/eosinophils as contaminants.

Which particles do monocytes readily ingest?

Polystyrene beads, Candida albicans, Cryptococcus neoformans, E. coli, Staph aureus, antibody‑coated RBCs.

Which particles do monocytes NOT ingest?

Aged RBCs, unsensitized RBCs, or neutrophils injured by endotoxin or leukoagglutinins.

Are monocytes or neutrophils more efficient at ingesting polystyrene beads?

Monocytes (93% vs. 73% at 30 min).

Does polystyrene phagocytosis require serum?

No, it occurs without serum.

Over what pH range does polystyrene phagocytosis occur?

Broad pH range (5.5–9.0).

Do monocytes phagocytose E. coli and Staph aureus?

Yes — but less efficiently than neutrophils

Does bacterial phagocytosis require serum?

Yes — serum greatly enhances ingestion.

Do monocytes ingest Candida albicans and Cryptococcus neoformans?

Yes — very efficiently with serum or opsonins

What opsonin is most effective for Candida?

IgG

Which cell type is better at ingesting Cryptococcus?

Monocytes (65% phagocytic) vs. neutrophils (6%).

Do monocytes ingest unsensitized RBCs?

No

What type of RBCs do monocytes ingest?

Antibody‑coated (IgG) RBCs.

What forms around monocytes during RBC phagocytosis?

Rosettes of RBCs around the monocyte.

What inhibits erythrophagocytosis?

Free IgG in the medium.

Do monocytes phagocytose neutrophils injured by endotoxin or antibodies?

No, despite increased contact.

What is the pH optimum for phagocytosis of RBCs and beads?

Broad pH range, similar to polystyrene ingestion.

Which metabolic pathway is essential for monocyte phagocytosis?

Glycolysis

Which inhibitors strongly block phagocytosis?

Sodium fluoride and iodoacetate (glycolysis inhibitors)

Which inhibitors have little effect?

Potassium cyanide (oxidative phosphorylation), actinomycin D, puromycin, cortisol.

What drug variably inhibits phagocytosis?

Colchicine

What drug strongly inhibits erythrophagocytosis?

Chloroquine

What metabolic pathway increases during monocyte phagocytosis?

Hexose monophosphate shunt (↑ C¹⁴O₂ from glucose‑1‑C¹⁴).

Does RNA or protein synthesis increase during early phagocytosis?

No significant increase.

How do neutrophils differ metabolically during phagocytosis?

They show large increases in C¹⁴O₂ production, RNA synthesis, and lactate production.

Which cell type is better at ingesting bacteria?

Neutrophils

Which cell type is better at ingesting antibody‑coated RBCs and Cryptococcus?

Monocytes