Shutdown of class switch recombination by deletion of a switch region control element.

Upon activation, B lymphocytes can change the class of the antibody they express by immunoglobulin class switch recombination. Cytokines can direct this recombination to distinct classes by the specific activation of repetitive recombinogenic DNA sequences, the switch regions. Recombination to a particular switch region (s gamma 1) was abolished in mice that were altered to lack sequences that are 5' to the s gamma 1 region. This result directly implicates the functional importance of 5' switch region flanking sequences in the control of class switch recombination. Mutant mice exhibit a selective agammaglobulinemia and may be useful in the assessment of the biological importance of immunoglobulin G1.