FIG. 5.

Detection of complement bound to D39, WU2, and derivatives. (A and B) C3 bound to bacteria after opsonization in BALB/cByJ serum, detected by ELISA, as described in Materials and Methods. Comparable results were obtained following opsonization in CBA/N serum. The data are the averages for at least three experiments. For MA1025, MA139, and JD803, the data for two independently obtained derivatives were combined. The results were compared by using Student's t test. (A) Accessible surface-bound C3 after incubation in serum. MA1025 and MA139 were not significantly different from parent strains WU2 and D39, respectively. JD803 was significantly different from both WU2 and D39 (P = 0.02 and P = 0.002, respectively). WU2 and D39 were significantly different (P = 0.006). (B) Accessible surface-bound C3 after opsonization with the PspA-specific polyclonal antiserum followed by incubation in BALB/cByJ serum. JD803 was significantly different from D39 (P = 0.007) but not from WU2. D39 and WU2 were significantly different (P = 0.004). (C) Total bound C3. Equivalent numbers of bacteria opsonized in CBA/N serum were separated by SDS-PAGE and immmunoblotted by using peroxidase-conjugated anti-C3. Comparable results were obtained following opsonization in BALB/cByJ serum. The bands represent the C3b β-chain (65 kDa) and iC3b α-chain (46 kDa) fragments (40).