DIRECT EVIDENCE THAT GAMMA-1 AND GAMMA-3 SWITCHING IN HUMAN B-CELLS IS INTERLEUKIN-10 DEPENDENT

Interleukin-10 (IL-10) has various effects on B cell immunoglobulin (I g) production. Indirect evidence suggests that IL-IO functions as a sw itch factor for IgG production. In this study, the switch deleted Ig g ene DNA was isolated and characterized, as direct evidence that IL-IO induced isotype switching in human B cells. In addition, 16 chimeric I g fragments were isolated, representing deleted DNA generated by in vi tro isotype switching from mu to gamma in human B cells, following sti mulation with IL-10 and anti-CD40 monoclonal antibodies (CD40 mAb). Th ese clones consisted solely of S gamma 1/S mu and S gamma 3/S mu chime ric switch circular DNAs, no S gamma 2/S mu or S gamma 4/S mu switch D NA was observed. In addition, IL-10 alone induced only gamma 1 and gam ma 3 germ-line mRNA transcripts, as determined by restriction digestio n of the reverse transcription-polymerase chain reaction products. Thr ee modes of mu-gamma 3 isotype switching were detected: (1) direct swi tching; (2) internal deletion of S mu proceeding mu to gamma 3 switchi ng; and (3) internal deletion of S gamma 3 proceeding mu to gamma 3 sw itching. These results directly demonstrate that gamma 1 and gamma 3 s witching in human B cells is specifically induced by IL-10 in the pres ence of CD40 mAb. (C) 1997 Published by Elsevier Science Ltd.