IMMUNOGLOBULIN DOUBLE ISOTYPE-PRODUCING HYBRIDOMAS ISOLATED FROM AN AUTOIMMUNE (NZBXNZW)F1 MOUSE

In the sera of (NZB x NZW)F1 (B/W) mice that develop a lupus-like synd rome, increased levels of IgG antibodies (Ab) reacting with TNP have b een detected before the appearance of IgG anti-DNA Ab and clinical sym ptoms. A single injection of trinitrophenyl-bovine serum albumin (TNP/ BSA) in physiological saline into a young B/W mouse (3 months old), fo llowed by fusion of its splenocytes 3 days later, gave rise to hybrido mas simultaneously secreting IgM and IgG Ab with anti-TNP reactivity, Both mu and gamma chains were detected in culture supernatants by ELIS A, and double isotype-producing cells were labeled by immunofluorescen ce. Molecular analysis of two of these double isotype-producing hybrid omas showed the presence of mRNA coding for both mu and gamma chains o f Ig, and this gamma mRNA could be translated in vitro into a gamma he avy (H) chain. Comparison of the H chain variable-region sequences of IgM and IgG revealed 100% homology between mu and gamma VH genes in on e clone, while mu and gamma V-H genes showed only 80% homology in the other clone. Both clones produced a single kappa light (L) chain. Thes e two hybridomas, isolated from a B/W mouse, thus represent two differ ent mechanisms of double isotype expression: the first one corresponds to an IgM to IgG switch, while the second one reflects a lack of alle lic exclusion.