65. Biochemistry of blood. Blood plasma and blood serum. Plasma proteins – fractions, representative and biological role. Albumin. Acute-phase proteins. C-reactive protein (CRP). Haptoglobin, hemopexin. Transferrin, ferritin, ceruloplasmin. α 2- macroglobulin. α 1-antitrypsin. Complement system. Matrix metalloproteinases. Serum amyloid A (SAA). Plasma immunoglobulins. Participation of plasma proteins in inflammatory response.

Introduction

This topic describes the protein composition of blood plasma, the main plasma protein groups and their functions, the acute-phase response, the complement system, matrix metalloproteinases and immunoglobulins. It also explains how plasma proteins take part in inflammation.

Plasma and serum

• Plasma is the liquid part of anticoagulated blood. It contains fibrinogen and the clotting factors.
• Serum is the liquid left after clotting. Fibrinogen and most clotting factors have been consumed, but the other proteins are essentially unchanged.
• Total plasma protein is about 60 to 80 g/L. Albumin is about 35 to 50 g/L.
• Serum protein electrophoresis separates albumin and the alpha 1, alpha 2, beta and gamma globulin fractions. The gamma fraction is mainly immunoglobulin.

Albumin

• Albumin is made in the liver, at roughly 10 to 15 g a day, and has a half-life of about 20 days.
• It generates most of the plasma colloid osmotic pressure, which keeps fluid in the vessels.
• It carries fatty acids, bilirubin, calcium, hormones and many drugs, including warfarin.
• The free thiol group of cysteine 34 gives albumin some antioxidant activity.
• Low albumin, as in liver disease, nephrotic syndrome or malnutrition, causes oedema. Albumin is also a negative acute-phase protein, so it falls during inflammation.