Immunoglobulin gene organization of ultraviolet-illuminated human lymphoblastoid cell lines producing both IgM and IgG

We have studied the immunoglobulin gene organization of ultraviolet light (u.v.)-induced variant cells derived from an Epstein-Barr virus-transformed cell line. One variant produced IgG₁ and two variants produced both IgM and IgG₁ whereas the parental cell line produced IgM. Southern blot analyses of DNAs of these cells revealed a newly rearranged J(H) fragment in all the variants. The newly rearranged J(H) fragment also hybridized with the C(γ1) sequence. The μ and γ₁ chains produced in the double isotype-producing variants share the same V(H) sequence. u.v. illumination also induced rearrangement of the C(λ) gene in the IgG₁-producing variant. The double isotype producers contained the immunoglobulin gene organization and mutation best explained by fusion of the IgG₁ producer and the parental IgM producer.