Alpha-2-macroglobulin Concentrations in Human Serum

Abstract

RECENTLY, we noted that serum from patients with acute pancreatitis has a decreased ability to bind trypsin^1,2. Although it is known that this trypsin-binding activity is associated with alpha-2-macroglobulin (α₂-M)^1,3, the ultracentrifuge pattern of serum proteins of these patients showed no decrease in total macroglobulin. There have been a number of estimates of normal concentrations of α₂-M using immunological methods^4–6 which are substantially higher than earlier estimates involving complement fixation⁷ and ultracentrifugation⁸. Indeed, James et al.⁶ concluded from immunological determinations that the total macroglobulin was normally more than 5 per cent of total plasma protein, rather than the 2–3 per cent generally reported from ultracentrifuge studies⁹. Comparison of the values of α₂-M in serum determined immunologically with those determined by analytical ultracentrifugation made it necessary to measure gamma-macroglobulin (IgM) by immunoassay because the 19S fraction determined by ultracentrifugation represents both α₂-M and IgM. We believe that the lack of purity of the α₂-M is the cause of the high values recently reported.