The leucocoyte disappearance reaction in non-immune acute inflammation

Gata6+ large peritoneal macrophages: an evolutionarily conserved sentinel and effector system for infection and injury

There are striking similarities between the sea urchin cavity macrophage-like phagocytes (coelomocytes) and mammalian cavity macrophages in not only their location, but also their behaviors. These cells are crucial for maintaining homeostasis within the cavity following a breach, filling the gap and functioning as a barrier between vital organs and the environment. In this review, we summarize the evolving literature regarding these Gata6⁺ large peritoneal macrophages (GLPMs), focusing on ontogeny, their responses to perturbations, including their rapid aggregation via coagulation, as well as scavenger receptor cysteine-rich domains and their potential roles in diseases, such as cancer. We challenge the 50-year old phenomenon of the 'macrophage disappearance reaction' (MDR) and propose the new term 'macrophage disturbance of homeostasis reaction' (MDHR), which may better describe this complex phenomenon.

Pre/pro-B cells generate macrophage populations during homeostasis and inflammation

Most tissue-resident macrophages (Mφs) are believed to be derived prenatally and are assumed to maintain themselves throughout life by self-proliferation. However, in adult mice we identified a progenitor within bone marrow, early pro-B cell/fraction B, that differentiates into tissue Mφs. These Mφ precursors have non-rearranged B-cell receptor genes and coexpress myeloid (GR1, CD11b, and CD16/32) and lymphoid (B220 and CD19) lineage markers. During steady state, these precursors exit bone marrow, losing Gr1, and enter the systemic circulation, seeding the gastrointestinal system as well as pleural and peritoneal cavities but not the brain. While in these tissues, they acquire a transcriptome identical to embryonically derived tissue-resident Mφs. Similarly, these Mφ precursors also enter sites of inflammation, gaining CD115, F4/80, and CD16/32, and become indistinguishable from blood monocyte-derived Mφs. Thus, we have identified a population of cells within the bone marrow early pro-B cell compartment that possess functional plasticity to differentiate into either tissue-resident or inflammatory Mφs, depending on microenvironmental signals. We propose that these precursors represent an additional source of Mφ populations in adult mice during steady state and inflammation.

Annexin 1-deficient neutrophils exhibit enhanced transmigration in vivo and increased responsiveness in vitro

The role of the endogenous anti-inflammatory mediator annexin 1 (AnxA1) in controlling polymorphonuclear leukocyte (PMN) trafficking and activation was addressed using the recently generated AnxA1 null mouse. In the zymosan peritonitis model, AnxA1 null mice displayed a higher degree (50-70%) of PMN recruitment compared with wild-type littermate mice, and this was associated with reduced numbers of F4/80+ cells. Intravital microscopy analysis of the cremaster microcirculation inflamed by zymosan (6 h time-point) indicated a greater extent of leukocyte emigration, but not rolling or adhesion, in AnxA1 null mice. Real-time analysis of the cremaster microcirculation did not show spontaneous activation in the absence of AnxA1; however, superfusion with a direct-acting PMN activator (1 nM platelet-activating factor) revealed a subtle yet significant increase in leukocyte emigration, but not rolling or adhesion, in this genotype. Changes in the microcirculation were not secondary to alterations in hemodynamic parameters. The phenotype of the AnxA1 null PMN was investigated in two in vitro assays of cell activation (CD11b membrane expression and chemotaxis): the data obtained indicated a higher degree of cellular responses irrespective of the stimulus used. In conclusion, we have used a combination of inflammatory protocols and in vitro assays to address the specific counter-regulatory role of endogenous AnxA1, demonstrating its inhibitory control on PMN activation and the consequent impact on the inflamed microcirculation.

Effects of TZI-41127, a novel selective 5-lipoxygenase inhibitor, on A23187-induced pleurisy in rats

Intrapleural injection of the ionophore A23187 in rats induced leukotriene (LT) production, prostaglandin E2 production, plasma exudation and leukocyte accumulation in the pleural cavity. We evaluated the inhibitory effects of orally administered drugs on 5-lipoxygenase activity by their ability to reduce the content of both peptido-LTs (LTC4, LTD4 and LTE4) and LTB4 in this model. TZI-41127, a novel selective 5-lipoxygenase inhibitor, significantly reduced the peptido-LTs and LTB4 content with ED50 values of 4.2 and 6.1 mg/kg, respectively, whereas it only reduced the prostaglandin E2 content (cyclooxygenase activity) by 31.1% even after 100 mg/kg. Phenidone inhibited 5-lipoxygenase activity more selectively than cyclooxygenase activity. BW755C inhibited cyclooxygenase activity more selectively than 5-lipoxygenase activity. Indomethacin selectively inhibited cyclooxygenase activity. These results suggest that: (1) A23187-induced pleurisy is an convenient in vivo model for studying drug effects on 5-lipoxygenase and cyclooxygenase activities and (2) TZI-41127 is an orally active and comparatively selective inhibitor of 5-lipoxygenase activity.

Sequential study of pleural peritoneal and blood cells in acute pleurisy induced by calcium pyrophosphate in the rat

We studied the sequential cellular events that occur during nonspecific pleurisy induced by a nondiffusible, nonantigenic and endotoxin-free irritant, calcium pyrophosphate (CaPP). The study was conducted over 10 days and concerned not only the pleural cavity but also the peritoneal cavity and the blood. After injection of CaPP, the first cellular event in the pleural space was a "leukocyte disappearance reaction," followed by an important increase in the polymorphonuclear leukocytes (PMN) and then by an increase in the macrophages. This phase is also characterized by the appearance of submesothelial nodules composed of macrophages and numerous polymorphonuclear cells. All the cell populations returned to their normal value on day 10, although granulomatous submesothelial nodules were present. In the blood, the principal observation was an increased PMN count associated with a decreased lymphocyte count at 4 h. In the peritoneal cavity, it was remarkable that, although functional modifications have been reported in the same model, the different leukocyte populations did not vary during the reaction.

Exudative, cellular and humoral reactions to platelet-activating factor (PAF-acether) in the pleural cavity of rats

The reactions to platelet-activating factor (PAF-acether) injected into the pleural cavity of rats were compared with the reactions in animals injected with 0.9% NaCl. PAF-acether induced a maximum exudate after 30-60 min, which then decreased and disappeared after 24 h. The number of pleural leukocytes in the exudate was clearly decreased 30 min after the injection, was slightly increased after 6 h and was unchanged at other times. The estimation of lipid mediators in the pleural exudate obtained 30 and 60 min after the injection of PAF-acether revealed an increase in type-C4 leukotriene (LTC4) and a decrease in thromboxane B2 (TxB2) and in 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha). In addition, the amount of histamine was found to be lower after 30 min. These results confirm in vivo that some biological effects of PAF-acether seem to involve the participation of other mediators.

Modification of thymo-dependent and thymo-independent antibody responses during non-specific acute inflammation

An acute non-immunological inflammatory reaction, induced in mice by injecting intrapleurally a non-bacterial, non-antigenic and endotoxin-free irritant (40,000 molecular weight dextran or monoclinic dihydrated calcium pyrophosphate microcrystals), provoked an increase of antibody responses to thymus-dependent SRBC or thymus-independent TNP-LPS or DNP-Ficoll when the phlogistic stimulus was applied before immunisation. The increase in the number of IgM plaque-forming cells per spleen was obtained for different time intervals between the induction of the inflammatory stimulus and the antigen administration according to the type of irritant and the antigen used. However, no stimulation could be observed when this time interval was greater than three days. No stimulation of the antibody response to SRBC was observed when the irritant was applied one to three days after the antigen. The (stimulatory) effect could not be entirely related to a polyclonal activation as an augmentation in the production of antibody against non-cross-reactive antigen could only be seen four days after the onset of the inflammatory process, when the specific antibody response was not maximal. These observations indicate that an acute non-immunological inflammatory reaction lasting for 48 h can affect the immune reactivity of the host, even after the inflammatory process has disappeared.

Leukocyte migration inhibition activity of nonimmune acute inflammatory pleural exudate

Material with leuckocyte migration inhibition (LMI) activity has been demonstrated in various types of nonimmunologically induced acute pleural inflammatory exudates. This activity is present in inflammatory cell-free exudate and appears to involved the deposition of fibrin around the migrating leukocyte, resulting in "cell-trapping." This is supported by the fact that removal or inhibition of fibrin formation leads to loss of exudate LMI activity. Both fibrinogen and complement as well as vitamin K-dependent clotting factors appear to be required for LMI activity. The mechanism involved in the LMI reaction and its significance in nonimmune and cell-mediated immune inflammation are discussed.