Complement activation during OKT3 treatment: a possible explanation for respiratory side effects

Area of Science:

• Immunology
• Pharmacology
• Pulmonary Medicine

Background:

• Anti-CD3 monoclonal antibody OKT3 is used for antirejection therapy.
• Respiratory side effects are a known complication of OKT3 treatment.
• The mechanism behind these side effects is not fully understood.

Purpose of the Study:

• To investigate the role of complement activation and neutrophil sequestration in OKT3-induced respiratory side effects.
• To examine the temporal relationship between OKT3 administration, complement activation, neutrophil behavior, and cytokine release.

Main Methods:

• Nine patients receiving OKT3 for antirejection treatment were studied.
• Plasma levels of complement activation products (C3a-desarg, C4b/c) and neutrophil degranulation markers were measured.
• Pulmonary sequestration of radiolabeled granulocytes was assessed.
• Cytokine levels (TNF alpha, IL-6, IL-8) were monitored.

Main Results:

• The first dose of OKT3 caused rapid increases in complement activation and neutrophil degranulation markers.
• Pulmonary sequestration of activated granulocytes and peripheral granulocytopenia occurred within minutes of the first OKT3 dose.
• These effects were not observed with subsequent OKT3 doses or with methylprednisolone treatment.
• Cytokine elevation occurred later than complement activation and neutrophil sequestration.

Conclusions:

• Immediate complement activation and pulmonary sequestration of activated neutrophils follow the first dose of OKT3.
• These early events are likely responsible for the respiratory side effects associated with OKT3 therapy.
• Targeting complement or neutrophil activation may mitigate OKT3-related adverse events.