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Role of polymorphonuclear leukocytes in connective tissue breakdown during the reverse passive Arthus reaction
Abstract:
The reverse passive Arthus (RPA) reaction performed in the skin of rats was modified to allow for the determination of polymorphonuclear leukocyte (PMN) infiltration and hemorrhage, as well as changes in vascular permeability. After initiation of the RPA reaction, PMN infiltration, monitored by measurement of tissue myeloperoxidase (MPO, EC 1.11.1.7) content, increased dramatically with time. Depending on the experimental conditions used, PMN accumulation reached a maximum 2-10 hr after increased vascular permeability (125I-labeled albumin content) had peaked. Hemorrhage (59Fe-labeled erythrocyte accumulation) began to occur only after significant levels of PMN were reached and continued to increase proportionately to the level of PMN infiltration attained. Indomethacin administered 30 min prior to initiating the RPA reaction had no effect on vascular permeability increase but suppressed both PMN accumulation and hemorrhage development about 50%. When indomethacin was given 2 hr after the RPA reaction was begun, no effect on any of the RPA variables was noted. Dexamethasone suppressed the increase in vascular permeability (53%), PMN accumulation (78%), and hemorrhage (90%) when given 30 min prior to initiation of the reaction. Dexamethasone given 2 hr after initiating the RPA suppressed the entire reaction, but to a lesser extent. Catalase, as well as trasylol, alpha-1-antiproteinase and soybean trypsin inhibitor, inhibited PMN accumulation as well as hemorrhage when given intravenously at plus 2 hr. These results indicate that the damage to blood vessels during a severe RPA reaction is a direct consequence of PMN activity.
Insights
Polymorphonuclear leukocyte (PMN) activity directly causes blood vessel damage during reverse passive Arthus (RPA) reactions. Inhibiting PMN infiltration significantly reduces hemorrhage and vascular permeability in this model.
Area of Science:
- Immunology
- Pathology
Background:
- The reverse passive Arthus (RPA) reaction is a model for studying acute inflammation.
- Understanding the cellular and molecular mechanisms of RPA is crucial for developing anti-inflammatory therapies.
Purpose of the Study:
- To modify the rat RPA reaction for quantifying polymorphonuclear leukocyte (PMN) infiltration, hemorrhage, and vascular permeability.
- To investigate the role of PMN activity in mediating vascular damage during RPA.
Main Methods:
- RPA reaction induced in rat skin.
- Quantification of PMN infiltration via myeloperoxidase (MPO) activity.
- Measurement of vascular permeability using 125I-labeled albumin.
- Assessment of hemorrhage by 59Fe-labeled erythrocyte accumulation.
- Pharmacological interventions with indomethacin, dexamethasone, catalase, trasylol, alpha-1-antiproteinase, and soybean trypsin inhibitor.
Main Results:
- PMN infiltration, vascular permeability, and hemorrhage increased over time following RPA initiation.
- PMN accumulation peaked after vascular permeability but preceded significant hemorrhage.
- Indomethacin suppressed PMN infiltration and hemorrhage but not vascular permeability when given early.
- Dexamethasone inhibited all measured variables, with greater suppression when administered preemptively.
- Protease inhibitors and catalase reduced PMN infiltration and hemorrhage when given 2 hours post-RPA initiation.
Conclusions:
- PMN activity is the direct cause of blood vessel damage in severe RPA reactions.
- The timing of therapeutic intervention is critical for efficacy in modulating RPA-induced inflammation and damage.