Ig heavy chain class switching in rag-deficient mice.

To investigate potential roles of the RAG-1 and RAG-2 gene products in Ig heavy chain class recombination (CSR), we have generated RAG-1-/- and RAG-2-/- mice which contain both a rearranged IgHC V(D)J gene (referred to as B1-8) inserted into the endogenous Ig heavy chain (HC) locus in place of the JH segments, and a rearranged δ1 light chain (LC) transgene (which are referred to as RAG-1-/-B1-8δ and RAG-2-/-B1-8δ mice respectively). The B1-8 HC gene and δ LC genes encode proteins that associated to form a complete Ig molecule, the expression of which leads to substantial reconstitution of the peripheral B cell compartments of RAG-1-/-B1-8δ and RAG-2-/-B1-8δ mice. Both RAG-1-/-B1-8δ and RAG-2-/-B1-8δ mice have relatively normal levels of the various IgG isotypes, but greatly reduced levels of serum IgM and IgA compared to normal littermates. Furthermore, RAG-1-/-B1-8δ and RAG-2-/-B1-8δ B cells activated in vitro with lipopolysaccharide (LPS) or LPS plus IL-4 responded similarly to control B cells with respect to surface expression and secretion of IgG3, IgG1, IgG2b, IgG2a and IgE, but again were deficient in the secretion of IgM. Together, these findings indicate that neither RAG-1 nor RAG-2 expression is required for efficient class switching to most HC isotypes in B cells. [ABSTRACT FROM PUBLISHER]