Studies in the alymphoplasia (aly/aly) and Nik-knockout mice described B cell deficiency due to disorganized lymph nodes, Peyer’s patches and splenic architecture, accompanied by B cell lymphopenia and low serum Ig levels due to compromised class switch recombination (CSR) and somatic hypermutation (SHM) (8, 9, 11, 13, 24, 29). This evidence concerns the gene MAP3K14 and B cell deficiency.