This strain is an Ighj-deletion model, in the homozygous B6-Ighj KO mice, the J-segment of the Ig heavy chain locus is completely deleted, resulting in the inability of the cell to produce a recombinant version of the complete heavy chain variable region. The B cells of B6-Ighj KO mice have undergone dramatic changes in the developmental process and cell number, which can be used as an animal model of B-cell immune deficiency. B6-Ighj KO mice retain other immune cells except for B cells, so the presence of other immune cells can be detected in B6-Ighj KO mice.