Depletion of pulmonary intravascular macrophages rescues inflammation-induced delayed neutrophil apoptosis in horses

The objective of this study was to determine the effect of pulmonary intravascular macrophage depletion on systemic inflammation and ex vivo neutrophil apoptosis, using an experimental model of intestinal ischemia and reperfusion injury in horses. Neutrophils were isolated before and after surgery from horses that were randomized to 3 treatment groups: sham celiotomy (CEL, n=4), intestinal ischemia and reperfusion (IR, n=6), intestinal ischemia and reperfusion with gadolinium chloride treatment to deplete pulmonary intravascular macrophages (PIMs, IRGC, n=6). Neutrophil apoptosis was assessed with Annexin V and propidium iodide staining quantified with flow cytometry and caspase-3, -8, and -9 activities in neutrophil lysates. All horses experienced a systemic inflammatory response following surgery. Following surgery, ex vivo neutrophil apoptosis was significantly delayed after 12 or 24 h in culture, except in IRGC horses (12 h: CEL: P = 0.03, IR: P = 0.05, IRGC: P =0.2; 24 h: CEL: P = 0.001, IR: P = 0.004, IRGC: P = 0.3). Caspase-3, -8, and -9 activities were significantly reduced in neutrophils isolated after surgery and cultured for 12 h in IR horses, but not IRGC horses (IR caspase-3: P = 0.002, IR caspase-8: 0.002 P =, IR caspase-9: P = 0.04). Serum TNF-α concentration were increased in IRGC horses for 6-18 h following jejunal ischemia. Following surgery, ex vivo equine neutrophil apoptosis was delayed via down-regulation of caspase activity, which was ameliorated by PIM depletion potentially via upregulation of TNF-α.

Human Clinical Relevance of the Porcine Model of Pseudoallergic Infusion Reactions

Pigs provide a highly sensitive animal model for pseudoallergic infusion reactions, which are mild-to-severe hypersensitivity reactions (HSRs) that arise following intravenous administration of certain nanoparticulate drugs (nanomedicines) and other macromolecular structures. This model has been used in research for three decades and was also proposed by regulatory bodies for preclinical assessment of the risk of HSRs in the clinical stages of nano-drug development. However, there are views challenging the human relevance of the model and its utility in preclinical safety evaluation of nanomedicines. The argument challenging the model refers to the “global response” of pulmonary intravascular macrophages (PIM cells) in the lung of pigs, preventing the distinction of reactogenic from non-reactogenic particles, therefore overestimating the risk of HSRs relative to its occurrence in the normal human population. The goal of this review is to present the large body of experimental and clinical evidence negating the “global response” claim, while also showing the concordance of symptoms caused by different reactogenic nanoparticles in pigs and hypersensitive man. Contrary to the model’s demotion, we propose that the above features, together with the high reproducibility of quantifiable physiological endpoints, validate the porcine “complement activation-related pseudoallergy” (CARPA) model for safety evaluations. However, it needs to be kept in mind that the model is a disease model in the context of hypersensitivity to certain nanomedicines. Rather than toxicity screening, its main purpose is specific identification of HSR hazard, also enabling studies on the mechanism and mitigation of potentially serious HSRs.

Pulmonary intravascular macrophages: prime suspects as cellular mediators of porcine CARPA

Pigs provide a highly sensitive and quantitative in vivo model for complement (C) activation-related pseudoallergy (CARPA), a hypersensitivity reaction caused by some state-of-art nanomedicines. In an effort to understand the mechanism of the pigs’ unique sensitivity for CARPA, this review focuses on pulmonary intravascular macrophages (PIMs), which are abundantly present in the lung of pigs. These cells represent a macrophage subpopulation whose unique qualities explain the characteristic symptoms of CARPA in this species, most importantly the rapidly (within minutes) developing pulmonary vasoconstriction, leading to elevation of pulmonary arterial pressure. The unique qualities of PIM cells include the following; 1) they are strongly adhered to the capillary walls via desmosome-like intercellular adhesion plaques, which secure stable and lasting direct exposition of the bulk of these cells to the blood stream; 2) their ruffled surface engaged in intense phagocytic activity ensures efficient binding and phagocytosis of nanoparticles; 3) PIM cells express anaphylatoxin receptors, this way C activation can trigger these cells, 4) they also express pattern recognition molecules on their surface, whose engagement with certain coated nanoparticles may also activate these cells or act in synergy with anaphylatoxins and, finally 5) their high metabolic activity and capability for immediate secretion of vasoactive mediators upon stimulation explain the circulatory blockage and other robust physiological effects that their stimulation may cause. These qualities taken together with reports on liposome uptake by PIM cells during CARPA and the possible presence of these cells in human lung suggests that PIM cells may be a potential therapeutic target against CARPA.