Both B1a and B1b cells produce IgM_Ft.

Rag1^-/- mice reconstituted with purified B1a or B1b cells were immunized i.p. with LPS_Ft. (A) Total number of peritoneal B1a or B1b cells in reconstituted Rag1^-/- mice. Level of IgM_Ft and total IgM in serum was measured on day 7 p.i. (B) Reconstituted Rag1^-/- mice were then infected with Ft (4x10³ cfu) and euthanized seven days later for measurement of bacteria burdens in organs. One representative experiment of two is shown. Data are expressed as mean ± SD. One-way ANOVA Tukey Post-test. *p<0.05, **p<0.01, ****p<0.0001. See also S2 Fig.