CR1/2 on B cells and FDCs is required for optimal antibody responses to IgM-SRBC complexes.

<p>BALB/c and <i>Cr2^−/−</i> mice were irradiated and reconstituted with either BALB/c or <i>Cr2^−/−</i> bone marrow. Six weeks after transplantation, mice were immunized with 5×10⁵ (A–D) or 5×10⁶ (E–H) SRBC alone (open squares) or together with IgM anti-SRBC with a hemagglutination titer of 1∶32 (filled squares) or with IgM anti-SRBC alone (open triangles) (n = 6/group). All mice were bled at indicated time points. Sera were diluted 1∶25 (A–D) or 1∶625 (E–H) and screened for IgG anti-SRBC. Two statistical comparisons were made, both using Student's <i>t</i>-test. First, comparisons between the responses in mice immunized with SRBC alone versus IgM and SRBC (to determine whether IgM enhanced antibody responses significantly; filled versus open symbols), where ns = p>0.05; * = p<0.05; ** = p<0.01; *** = p<0.001. Second, comparisons between the responses between various chimeras immunized with IgM-SRBC (to determine whether CR1/2⁺ B cells contributed significantly to the antibody response to IgM-SRBC in mice with CR1/2⁺ FDCs (A vs B; E vs F) and CR1/2⁻ FDCs (C vs D; G vs H)), where ns = p>0.05; ° = p<0.05; °° = p<0.01; °°° = p<0.001. For graphic clarity, non-significant differences are not indicated. Representative of one (A–D) and two (E–H) experiments.