Fig 1. IgG-mediated suppression of primary IgM-responses in C1q KO and C3 KO mice.

C1q KO, C3 KO, and C57BL/6 mice were immunized with 50 μg IgG^a anti-SRBC and 5x10⁷ SRBC, 5x10⁷ SRBC alone, or with 50 μg IgG^a alone. (A,B) Five days after immunization, the number of spleen cells producing IgM anti-SRBC was assayed. Responses are shown as percentage of the direct PFC response/spleen in mice given SRBC alone (100%, open bars); black bars show responses in mice given IgG and SRBC. Direct PFC/spleen in the respective control groups (receiving antigen alone) were in A: C57BL/6, 56,105; C1q KO, 5,433 and in B: C57BL/6, 54,954; C3 KO, 3,614. Data are pooled from three experiments; (n = 4/group in each experiment). p-values denote comparisons between mice immunized with IgG anti-SRBC together with SRBC and mice immunized with SRBC alone. ***, p < 0.001.