It has been observed earlier that the
hemolytic complement in diluted sera obtained from patients with
hereditary angioedema (HAE) undergoes spontaneous decay when incubated at 37 degrees C. Employing individual serum from patients at different stages of this disease it was demonstrated that this spontaneous loss of
hemolytic complement also occurs without dilution and is directly linked to the absence of functional C-1-INA. Incubation of HAE serum resulted in a loss of activity which appears to be dependent upon the concentration of functional C-1-INA. While C-1-INA levels less than 50 micrograms/ml lead to rapid depletion with time, reconstitution of deficient sera with highly purified C-1-INA or of undiluted NHS inhibited spontaneous activation. Furthermore, NHS was rendered susceptible to autoactivation when its C-1-INA was depleted by passage over an anti-C-1-INA
Sepharose 4B affinity column in the presence of 10 mM
EDTA, indicating that in the absence of functional C-1-INA, C1 undergoes an uninhibited spontaneous autoactivation which leads to the consumption of C4 and C2 but not C3. Consumption of C3 was observed, however, in HAE sera that contained a significant amount of
immune complexes. Incubation of HAE sera with highly purified
Hageman factor fragment (5 micrograms/ml), or aggregated
IgG (2 mg/ml) was found to accelerate the rate of decay when compared to untreated samples while sera from patients under treatment with
Danazol or
Stanozolol failed to autoactive. These results suggest that, the absence of C-1-INA, may, by itself trigger the dissociation and autoactivation of C1 in the sera of such patients; however, the presence of other
complement activators accelerates the reaction. This inherent property of HAE sera, i.e., spontaneous autoactivation at 37 degrees C, may be a useful screening test but direct determination of C-1-INA activity is required to establish the precise diagnosis.