Characterization of the adaptive immune response toward L major in B6.Ceacam1^−/− and B6.WT mice. (A,B) Quantification by enzyme-linked immunosorbent assay (ELISA) of L major–specific immunoglobulins in serum, IgG₁ (A) and IgG_2b (B) on days 20 and 40 after infection. The amounts of the L major–specific antibodies are expressed as relative ELISA units. Each symbol represents data from one B6.WT (■) or B6.Ceacam1^−/− mouse (○; n = 6 each). Horizontal lines in (A) and (B) indicate the mean. (C) Proliferation of lymph node cells from naive B6.WT mice and B6.Ceacam1^−/− and B6.WT mice on day 21 after infection after treatment with cell culture medium (□), ConA (■), and L-Ag (▧) expressed in counts per minute (cpm) after H³-thymidine incorporation. Data shown here summarize mean (± SEM) from 6 animals per group. (D) Quantification of IFN-γ production in supernatants from lymph node cells from naive B6.WT mice and from B6.WT and B6.Ceacam1^−/− mice after infection with L major on day 21 after infection in response to medium (□), ConA (■), or L-Ag (▧). Data are summarized as mean (± SEM) from 6 mice per group (n.d. indicates not detectable).