FIG. 1.

Passive Ab protects mice lacking C3. (A) Survival of C3^−/− mice infected with C. neoformans after i.p. administration of 1.0 mg of 3E5 IgG1 (▪), IgG2a (▴), IgG2b (▾), or IgG3 (•) anti-GXM SCID ascites fluid or 1.0 ml of control NSO (○) SCID ascites fluid 24 h prior to i.v. challenge with 5 × 10⁵ C. neoformans cells. There were 8 to 11 mice in each group. The median survival times (± standard deviations) for the IgG1, IgG2a, IgG2b, IgG3, and NSO groups were 22 ± 8, 27 ± 7, 10 ± 2, 14 ± 7, and 3 ± 0 days, respectively. All isotypes prolonged animal survival significantly (P < 0.0009). (B) Survival of C. neoformans-infected C57BL/6J mice depleted of C3 by CVF. Twenty-four hours after CVF injection, the mice were given 1.0 mg of 3E5 IgG2a (▴), IgG2b (▾), or IgG3 (•) anti-GXM SCID ascites fluid or 1.0 ml of control NSO (○) SCID ascites fluid 24 h prior to i.v. challenge with 10⁵ yeast cells. NSO-treated mice not given CVF are also shown (□). There were 9 to 11 mice in each group. After 35 days, all control mice treated with CVF had died (median survival time, 31 ± 7 days), whereas there were no deaths among animals that received Ab or control mice that did not receive CVF (P < 0.002).