Factor J, an inhibitor of the classical and alternative complement pathway, does not inhibit esterolysis by factor D

Area of Science:

• Immunology
• Biochemistry
• Complement System

Background:

• Factor J (FJ) is recognized as an inhibitor of both the classical and alternative complement pathways.
• FJ disrupts complement component C1 in the classical pathway and the C3 convertase (C3b,Bb) in the alternative pathway through direct interactions.

Purpose of the Study:

• To investigate the potential inhibitory effect of Factor J on the proteolytic activity of factor D.
• To clarify previous findings that could not definitively rule out an interaction between Factor J and factor D.

Main Methods:

• Enzymatic activity of serine proteinase factor D was assessed using two specific peptide thioester substrates.
• Reactivity assays were conducted both in the presence and absence of Factor J.
• Kinetic studies were performed to analyze the interaction.

Main Results:

• Kinetic analyses demonstrated that Factor J had no discernible effect on the enzymatic activity of factor D.
• Factor J did not alter the proteolytic function of factor D under the tested conditions.

Conclusions:

• Factor J does not inhibit the serine proteinase activity of factor D.
• This study clarifies the specific interactions within the complement system, indicating Factor J's role is not through factor D inhibition.