Immunoglobulin M: fixation of human complement by the Fc fragment

Area of Science:

• Immunology
• Biochemistry

Background:

• Waldenström's macroglobulinemia is characterized by the overproduction of monoclonal IgM.
• The Fc fragment of immunoglobulin M plays a crucial role in complement activation.

Purpose of the Study:

• To investigate the complement-fixing ability of the Fc fragment of human immunoglobulin M (IgM) from Waldenström's macroglobulinemia patients.
• To compare the complement-fixing ability of the Fc fragment with the parent IgM molecule.

Main Methods:

• Isolation and characterization of the Fc fragment from IgM of Waldenström's macroglobulinemia patients.
• Assessment of complement fixation using human and guinea pig complement.
• Reduction of the Fc fragment to its monomeric form and re-evaluation of complement fixation.

Main Results:

• The Fc fragment of human IgM from Waldenström's macroglobulinemia patients exhibited approximately 19-fold greater molar complement-fixing ability compared to the parent IgM.
• The pentameric Fc fragment effectively fixed human complement but not guinea pig complement.
• Complement-fixing activity remained unaltered after reduction to the monomeric form.

Conclusions:

• The Fc fragment of human IgM in Waldenström's macroglobulinemia possesses a significantly enhanced capacity for complement fixation.
• The pentameric structure is not essential for the complement-fixing function of this fragment.
• These findings contribute to understanding the immunopathology of Waldenström's macroglobulinemia.