Pace of macrophage recruitment during different stages of soft tissue infection: Semi-quantitative evaluation by in vivo magnetic resonance imaging

Abstract

We describe the pace of recruitment of iron-oxide-labeled macrophages to the site of different stages of infection by in vivo magnetic resonance (MR) imaging. Peritoneal macrophages were labeled with superparamagnetic iron oxide ex vivo and administered through the tail vein 6 (acute) or 48 (subacute) h after bacterial inoculation. The legs of the mice were imaged sequentially on a 4.7-T MR unit before and 3, 6, 12, 18, 24, 48 and 72 h after macrophage administration. The band-shaped lower signal intensity zone around the abscess on T2*-weighted GRE images became more obvious due to recruited macrophages up until 24 h after injection in the subacute and 48 h after injection in the acute group, indicating that the relative SI of the abscess wall decreased more rapidly and the pace of recruitment of macrophages was faster in the subacute than in the acute group. Chemokine antibody arrays of mouse sera detected increased concentration of granulocyte-colony-stimulating factor and tissue inhibitor of metalloproteinase-1 beginning at 12 h and increased interleukin-13 at 18 h. Monocyte chemoattractant protein-1 and macrophage-colony-stimulating factor began to increase at 96 h after infection. This difference in pace of recruitment may result from the release of chemokines.

Neutrophil extracellular traps enhance macrophage killing of bacterial pathogens

“…Phagocytosis of infected apoptotic neutrophils allows Mφs to acquire functionally active myeloperoxidase (MPO), lactoferrin, and defensins from neutrophil granules, thereby enhancing antimicrobial activity (33)(34)(35)(36); however, this phenomenon has only been observed in response to intracellular bacterial pathogens. During staphylococcal infection, both neutrophils (37,38) and Mφs (39)(40)(41)(42) aid in the formation and maintenance of abscesses, putting these cells in close proximity. Yet, most host-pathogen interactions studies involving S. aureus have been assessed using isolated immune cells or whole blood lacking mature Mφs.…”

Macrophages Homing to Metastatic Lymph Nodes Can Be Monitored with Ultrasensitive Ferromagnetic Iron-Oxide Nanocubes and a 1.5T Clinical MR Scanner

“…First, the macrophages could be easily labeled with the FIONs, within a two-hour time periods. Although previous studies have reported that an overnight incubation was required to label the macrophages with Feridex [20], [21], [22], the intracellular iron concentration in the macrophages labeled with FIONs for 2 h was higher than the concentration found after a 24 h Feridex labeling (Figure S2). In theory, the short labeling time would improve the viability and functionality of the transplanted macrophages.…”

Pathogenic Role of Macrophages in Intradermal Infection of Methicillin-Resistant Staphylococcus aureus in Thermally Injured Mice

“…This process is triggered by bacteria and tissue M (35). Generally, M appear in abscesses of individuals with infection (7,17,26). Therefore, in this paper, we investigated the pathogenetic role of these M accumulated in the infection site tissue by use of a mouse model of burn injury with intradermal infection of MRSA.…”

“…Histologically, the abscess lesions consist of accumulating leukocytes with live bacteria (26). In recent studies (7,17,26), abscess formation was caused by the accumulation of phagocytic M to eliminate the pathogen. In this study, the influence of severe burn injury on abscess formation and bacterial growth at the infection site tissue was investigated for burned mice intradermally infected with MRSA.…”