FIG.4.

B-cell activation and humoral immune responses in Sly1^d/d mice. B220⁺ CD21^int CD23^hi follicular B cells (a) and B220⁺ CD21^hi CD23^lo marginal zone B cells (b) were purified from spleens of wild-type (white bars) and Sly1 mutant (solid bars) mice and were stimulated with anti-IgM and anti-CD40 or 40 ng/ml lipopolysaccharide (LPS). [³H]thymidine incorporation was measured after 3 days (n = 4 experiments). (c) Basal levels of immunoglobulin isotypes were determined in serum of untreated mice (n = 17 to 19 mice per group). (d) Levels of IgM in the peritoneal lavage (n = 8 to 9 mice per group). (e) For analysis of T-independent antibody responses, the time course of TNP-specific IgM and IgG3 antibody levels was determined in serum of wild-type (triangles) and Sly1 mutant (circles) mice immunized with TNP-Ficoll (n = 7 to 8 mice per group). (f) T-dependent production of TNP-specific antibody isotypes was measured after immunization of mice with TNP-CGG adsorbed to alum (n = 4 mice per group for day 4 and day 7; n = 8 mice per group for day 0, day 14, and day 21). *, P < 0.05; **, P < 0.01; ***, P < 0.001 (Student's t test).