Alpha 2-macroglobulin-kallikrein complexes detect contact system activation in hereditary angioedema and human sepsis

Abstract

Activation of the contact system has been documented in severe sepsis and hereditary angioedema, but a sensitive, specific, and quantitative assay for assessing the degree of involvement of this proteolytic enzyme cascade is not yet available. We have developed a quantitative sandwich enzyme-linked immunosorbent assay (ELISA) for the alpha 2- macroglobulin-kallikrein (alpha 2M-Kal) complex using an F(ab')2 derivative of a monospecific polyclonal antibody against alpha 2 M as the capture antibody and a unique murine monoclonal antibody, 13G11, against the heavy chain of kallikrein as the detector antibody. The assay does not detect complexes in normal plasma but reacts with complexes generated by activating normal plasma with dextran sulfate at 4 degrees C in a range of 5 to 375 nmol/L. A close correlation of the ELISA with an amidolytic assay for alpha 2M-Kal was documented. Patients with sepsis syndrome but negative bacterial blood cultures did not show elevated plasma complexes, whereas a majority of those with positive blood cultures did show modest elevation and a single patient with septic shock showed a very high level of alpha 2M-Kal complex. Similarly, a patient with classic hereditary angioedema (HAE) showed increased concentration of complexes on three separate occasions during attacks but normal levels between attacks. Two other HAE patients did not show elevated levels at quiescent periods. The ELISA for alpha 2M- Kal appears to be sensitive, specific, and quantitative, and it can be used to reflect the degree of contact system activation in human sepsis and in HAE attacks.

C1 inhibitor function using contact‐phase proteases as target: evaluation of an innovative assay

“…We implemented specific experimental conditions rendering the method independent of α2M control (Fig. B), in line with the slower inhibition of KK by α2M than by C1Inh, which could explain why the presence of this inhibitor is not sufficient to prevent attacks in HAE patients . The assay's efficient performance was demonstrated by ROC curves, including patients with C1Inh‐HAE and AAE, revealing excellent markers and signifying this test's suitability for establishing a biological diagnosis of angioedema.…”

The cytokine‐mediated imbalance between coagulant and anticoagulant mechanisms in sepsis and endotoxaemia

“…As shown above, the contact system of coagulation does not play a significant role in the initiation of endotoxin-induced activation of coagulation. However, in septic patients low plasma levels of factor XII and prekallikrein and high plasma levels of complexes between kallikrein and C1 inhibitor or a 2 -macroglobulin and between factor XIIa and C1 inhibitor can be detected [15,19,20]. These findings indicate that the contact system is activated in septic patients, although not involved in coagulation activation.…”

Activated factor XI inhibits chemotaxis of polymorphonuclear leukocytes

“…In patients with a clinical suspicion of disseminated intravascular coagulation, markers of contact system activation are elevated [14,15]. In a baboon model of lethal bacteremia, an inhibitory mAb against FXII extended animal survival time [16].…”