Tacke F, Ginhoux F, Jakubzick C, van Rooijen NV, Merad M, Randolph GJ.
Immature Monocytes Acquire Antigens from Other Cells in the Bone Marrow and Present Them to T Cells After Maturing in the Periphery.
J Exp Med. 2006 Mar 20;203(3):583–97.
[toggle_content title=”Abstract”] Monocytes are circulating precursors for tissue macrophages and dendritic cells (DCs) but are not recognized to directly participate in antigen presentation. We developed techniques to label mouse monocyte subsets with particulate tracers in vivo. Gr-1 lo but not Gr-1 hi monocytes were stably labeled by intravenous injection of 0.5-μm microspheres. Gr-1 hi monocytes could be labeled when the microspheres were injected after systemic depletion of blood monocytes and spleen macrophages. In this condition, the phagocytic tracer was transferred to immature bone marrow monocytes by neutrophils and B cells that first carried the particles to the bone marrow. Moreover, antigens from B cells or proteins conjugated to the tracer particles were processed for presentation by monocytes and could induce T cell responses in the periphery. Cell-associated antigen taken up by bone marrow monocytes was retained intracellularly for presentation of the antigen days later when monocyte-derived DCs migrated to lymph nodes or in vitro after differentiation with granulocyte/macrophage colony-stimulating factor. These data reveal that immature monocytes unexpectedly sample antigen from the bone marrow environment and that they can present these antigens after they leave the bone marrow. [/toggle_content] [toggle_content title=”Clodronate Liposome Parameters”] [custom_table]
Clodronate Concentration Total Lipid Concentration Lipid Composition Lipid Mole % Liposome Type Control Liposomes
10 mg/ml 1 46 mg/ml EPC/Chol 86/14 MLV none

1 Clodronate and lipid concentrations assumed based on referenced paper.

[/custom_table][/toggle_content] [toggle_content title=”Animals and Dosing”] [custom_table]
Animal Description Clodronate Dose Dosing Method/Site Target Phagocytes Adjunct Dosing? Adjunct Dosing Route
C57BL/6 & BALB/c mice 2 250 µl intravenous CD115+, F4/80+ monocytes no NA

2 Base or background strain. Variants, mutants or otherwise genetically altered strains were also used in this study.

[/custom_table] [/toggle_content] [toggle_content title=”Notes”]
  1. Clodronate and lipid concentrations assumed based on referenced paper, although references provide conflicting information as to final clodronate concentrations.
  2. Reference for clodronate liposome preparation – van Rooijen N, Sanders A. Liposome mediated depletion of macrophages: mechanism of action, preparation of liposomes and applications. Journal of immunological methods. 1994;174(1-2):83–93.
[/toggle_content] [toggle_content title=”Results”]
  1. >90% of monocytes (based on estimate from figure) depleted in blood 18 h post-injection of liposomal clodronate and returned to baseline at 48 h.
  2. Depletion corresponded to reduced pulmonary permeability (vascular leakage) post-LPS challenge.
  3. Very large numbers of monocytes marginated in organs during low dose LPS challenge, therefore total monocyte count in blood grossly underestimates total number of monocytes in the vascular system (also true for neutrophils). This could result in larger-than-expected levels of inflammatory cytokines in the circulation during some inflammatory events.