Inhibition of IgG2abProduction by Ig Allotype-Specific T Cells Can Be Mediated without T–B Cell Contact

The growth of IgG2ab-producing CB101 myeloma cells, subcutaneously or intraperitoneally inoculated into histocompatible BALB/c Ighamice sensitized against this Ig allotype, was delayed by 2–4 weeks compared to normal mice. While IgG2abproduction was detected in the sera of 75–100% of normal mice, it was irreversibly inhibited in 100% of sensitized mice. IgG2absuppression (IgG2absup) was also systematically obtained in sensitized but not normal recipients, implanted ip with a 0.1-μm-pore diffusion chamber (DC) containing CB101 cells. This time, the specific IgG2absup was reversiblein vitroin the absence of anti-IgG2abT cells. Adoptive transfer, of unfractionated or T but not B splenocytes from their sensitized counterparts into normal mice, 1 day before DC implantation, induced IgG2absup as well. These results indicate that, in these experimental circumstances, IgG2absup can also be mediated by diffusible suppressive factors produced by the effector T cells, without direct T–B-cell contact.