Differences in the activity of the alternative pathway of complement in BALB/c and C57Bl/6 mice.

The deposition of C3b on the surface of zymosan was assessed in inbred strains of mice. Mg(2+)-EGTA plasma from C57Bl/6 and BALB/c mice was incubated with zymosan and deposited C3b was eluted by methylamine. Eluted C3b was detected and quantified by Western blot and an enzyme-linked immunosorbent assay. 3- to 4-fold more C3b was deposited on zymosan incubated with C57Bl/6 plasma than on zymosan incubated with BALB/c plasma (p < 0.01). Data on the kinetics of deposition of C3b suggest a faster and greater activity of the alternative pathway of complement (ACP) in C57Bl/6 than in BALB/c. Higher C3b deposition in C57Bl/6 plasma occurs in the presence of higher plasma factor H concentration (1.3-fold of BALB/c concentration; p < 0.01) and is accompanied by higher factor H deposition on zymosan (3- to 10-fold of BALB/c concentration; p < 0.01). Demonstrable differences in the activity of the proteins of the ACP may provide a biological basis for the genetic variation in innate resistance to infectious organisms observed in inbred strains of mice.