Figure 1.

Antibody expression in mice without L chain. (A) κ⁻ mice carry an Igκ locus disabled by insertion of neo into Cκ (reference 46); λ⁻ mice carry a Cre-loxP–mediated deletion of ∼120 kb encompassing all Cλ genes (reference 7); and μNR mice have neo inserted into Cμ exons 1 and 2 and express truncated μ H chains (reference 17). (B) The level of H chain Ig in serum from unimmunized mice was titrated in ELISA by binding to antibodies against IgM, IgG, Igκ, and Igλ. In L^−/− (κ^−/−λ^−/−) mice, 20–100 μg/ml H chain IgG without L chain was produced (shaded area). μNRL^−/− mice produce a similar level of IgG in addition to truncated IgM. In normal mice (NM), ∼10 mg/ml IgG was produced. Purified IgG (DB3; reference 47) served as a standard, and serum from animals with removed C genes (CΔ mice; reference 45) was used as a negative control. (C) L chain–deficient mice homozygous for μMT (L^−/−μMT^−/−) do not express H chain IgG in serum, whereas in L^−/− (heterozygous) μMT^+/− mice, concentrations were similar to those of L^−/− mice. At least five mutant mice from separate litters were compared with the SD indicated when greater than ±0.2. (D) Immunizations (1st and 2nd imm.) with OVA show specific antibody responses and an increase in total IgG (pre imm. compared with after immunization). Groups of mice contained at least six animals, and SDs for IgG are shown when individual serum titrations diverged >10%.