Human IL-6 promotes the generation of antigen-specific IgG-switched B cells in humanized mice. A total of 18, 24, and 12 antibodies cloned from IgG⁺ B cells in OVA-immunized RG SKI mice, RG SKI IL-6 mice, and control HD were tested by ELISA for OVA reactivity (A) and polyreactivity (C). Blue lines represent a mouse anti-OVA specific antibody (TOSG1C6) in (A) or polyreactive ED38 clone in (C). Except for the purified TOSG1C6 clone, all other tested antibodies are collected from cell culture supernatants. Solid black lines represent antibodies cloned from HD and solid red lines represent recombinant antibodies cloned from either immunized RG SKI or RG SKI IL-6 mice. Reactive antibodies are indicated by IgL designation followed by clone number. Horizontal dotted lines define the cutoff OD405nm for positive reactivity. The cutoff OD value was determined as twice the value of the average OD when all clones from RG SKI mice were pooled. The frequency of reactive (black area) and nonreactive (white area) clones is summarized in pie charts, with the total number of clones tested indicated in the center. (B) Increased IGHV mutation numbers in OVA-reactive vs non-OVA reactive clones from immunized RG SKI IL-6 mice. *P < .01. HD, healthy donors; OD, optical density.