Isolation and purification of human C1q from plasma

Area of Science:

• Biochemistry
• Immunology
• Proteomics

Background:

• Complement component C1q is crucial for the classical pathway of the complement system.
• High-purity C1q is essential for various immunological and biochemical assays.
• Existing purification methods may not efficiently remove all immunoglobulin G (IgG) contaminants.

Purpose of the Study:

• To develop and validate a robust 3-step purification protocol for human plasma C1q.
• To achieve high purity C1q with minimal IgG contamination.
• To assess the stability of purified C1q under specific storage conditions.

Main Methods:

• Euglobulin precipitation of human plasma.
• Chromatography using rabbit IgG-Sepharose and rabbit anti-human IgG-Sepharose affinity columns.
• SDS-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and non-reducing conditions.
• Assessment of C1q stability in a defined buffer at 4°C.

Main Results:

• A 3-step purification procedure yielded homogeneous C1q with approximately 40% recovery.
• Purified C1q demonstrated minimal IgG contamination (< 4 μg/mg C1q).
• SDS-PAGE confirmed the expected subunit composition of C1q under reducing and non-reducing conditions.
• Purified C1q remained stable for at least 1 year when stored at 4°C in a specialized buffer.

Conclusions:

• The described 3-step purification method is effective for obtaining highly pure and stable human C1q.
• This protocol efficiently removes both free and C1q-bound IgG.
• The purified C1q is suitable for use in downstream immunological and biochemical applications.