It was previously shown that when normal human serum and purified
properdin or serum containing nephritic factor were allowed to diffuse toward each other in
agar, a stainable precipitin line formed only in the presence of an intact alternative pathway. In the present study we have shown that when guinea pig erythrocytes were incorporated in
agar and normal human serum was allowed to diffuse toward
C3 nephritic factor-containing serum, a line of
hemolysis appeared that coincided with the stainable line. The line of
hemolysis only formed in the presence of C3,
factor B and Mg++, as does the
properdin or
C3 nephritic factor-induced stainable line. When C2-deficient serum was incorporated in
agar with guinea pig erythrocytes and serum samples containing nephritic factor were applied in wells, rings of lysis developed, the areas of which correlated significantly with nephritic factor activity. When partially purified nephritic factor (contaminated only with
IgG) or serum containing nephritic factor was subjected to electrophoresis in
agar-guinea pig erythrocyte
gels and overlaid with normal human serum, bands of lysis developed that required
factor B and C3. Lysis of guinea pig erythrocytes in this system appears to be due to insolubilization of alternative pathway convertases with activation of the membrane attack unit C5-C9.