Endogenous inhibitors of factor B

Area of Science:

• Immunology
• Complement System Biology

Background:

• Mouse factor B is a key component of the complement system.
• Certain cell types, like monocytic and L cells, non-secrete factor B but contain proteins that bind it.

Purpose of the Study:

• To identify and characterize proteins that bind mouse factor B in nonsecretor cells.
• To investigate the functional role of these proteins in inhibiting factor B activity.

Main Methods:

• Isolation and purification of proteins from L cell lysates.
• Separation of proteins using preparative SDS-polyacrylamide gel electrophoresis.
• Analysis of protein-factor B complex formation and inhibition assays.

Main Results:

• Four distinct proteins (25K, 28K, 33K, and 35K) were isolated.
• These proteins formed a 1:1 complex with mouse factor B.
• Proteins 25K and 28K inhibited the hemolytic activity of both native and activated factor B.
• Inhibitory activity was specific to factor B and not the second complement component.
• Antiserum against the 25K protein partially inhibited its activity.

Conclusions:

• Nonsecretor cells possess endogenous inhibitors of mouse factor B.
• These identified proteins represent novel regulators of the complement system.
• The 25K and 28K proteins are potent inhibitors of factor B hemolytic activity.