Increased expression of complement decay-accelerating factor during activation of human neutrophils

Area of Science:

• Immunology
• Cell Biology

Background:

• Decay-accelerating factor (DAF) is a membrane protein protecting blood cells from complement-mediated damage.
• Neutrophils (polymorphonuclear leukocytes, PMN) play critical roles in inflammatory responses.

Purpose of the Study:

• To investigate the expression and regulation of DAF on neutrophils during activation.
• To explore the mechanism of DAF upregulation and its role in neutrophil function.

Main Methods:

• Monoclonal antibodies were used for direct-binding studies and flow cytometry.
• Neutrophil activation was induced, and surface DAF expression was quantified.
• Studies included analysis of protein synthesis dependence, EDTA effects, and inhibitor sensitivity (trifluoperazine).

Main Results:

• Resting neutrophils express approximately 10^4 DAF molecules per cell.
• Surface DAF expression more than doubled upon neutrophil activation within minutes.
• Upregulation paralleled complement receptor types 1 and 3 (CR1 and CR3) and was independent of new protein synthesis.
• DAF upregulation was inhibited by trifluoperazine, suggesting involvement of intracellular Ca2+, calmodulin, or protein kinase C.
• Neutrophils from paroxysmal nocturnal hemoglobinuria patients, lacking surface DAF, failed to upregulate DAF upon activation, indicating synthesis or packaging defects.

Conclusions:

• Neutrophil activation rapidly translocates DAF to the cell surface, enhancing complement protection.
• This process is crucial for neutrophil survival and function at inflammatory sites with high complement turnover.
• DAF deficiency in paroxysmal nocturnal hemoglobinuria involves intracellular processing abnormalities.