Monoclonal antibodies (mAbs) were raised against human a2M. Five mAbs that bound to α2M in ELISA were further analyzed by a radioimmunoassay (RIA) for their reaction with three types of α2M: native α2M, chemically inactivated α2M (iα2M) (methylamine treated), and proteolytically iα2M. One mAb reacted with all forms of α2M, while four mAbs bound both forms of ia2M but not native α2M. One of these latter mAbs (Ml) was used to develop a RIA (the Ml-assay) for the detection of iα2M in plasma: Ml coupled to Sepharose is incubated with the plasma to be tested, and bound iα2M is detected by a subsequent incubation with polyclonal 125I-anti-α2M antibodies. As little as 5 ng of iα2M can be detected with this assay in the presence of an excess of native α2M. This assay was then applied to measure inactivation of α2M in vitro and in vivo. In vitro activation of the contact system in plasma by dextran sulfate results in the inactivation of ca 10% of α2M. When blood from normal donors was collected under optimal conditions, about 0.5% of the total α2M content appeared to be iα2M. Longitudinal studies in patients (a.o. with septicaemie, during cardiopulmunary bypass) revealed that increased levels of iα2M occurred sporadically. The Ml-assay appears to be useful to monitor the role of α2M in human diseases.
Inhibition of human activated Factor X by antithrombin III and alpha 1-proteinase inhibitor in human plasma.
