Activation of factor B of the alternative pathway of complement. Assessment by rocket immunoelectrophoresis.

During activation of the alternative pathway of complement, Factor B is cleaved into a smaller fragment Ba and a larger fragment Bb. The Ba in plasma was quantitated by one-dimensional rocket immunoelectrophoresis after precipitating plasma B and Bb with 21% polyethyleneglycol. This method was much more sensitive and faster than other technics with which it was compared. Fragment Ba was detected in 22 of 28 rheumatoid arthritis plasma samples and in 12 of 15 systemic lupus erythematous samples but in only 8 of 68 samples obtained from healthy volunteers. The traditional approach of measuring total Factor B for the assessment of activation of the alternative pathway showed values that were even higher than normal in these diseases. The measurement of plasma Ba promises to be a valuable means of assessment of the activation of Factor B and the alternative pathway of complement in clinical disorders.