Shifts from IgG-2 class to IgG-1 class in CBA and C3H anti-BALB/c antibody.

With use of a recently developed method for determining relative levels of IgG-1 and IgG-2 class antibodies of a given specificity within an unfractionated serum, it has been possible to examine anti-BALB/c antibodies in the early and late part of an immunization with allogeneic spleen cells. At about 6 days after primary immunization of CBA or C3H mice with BALB/c spleen cells, suppressive antibodies can be measured in the sera of the animals. About half of these are attributable to IgM class, and this contribution decreases to zero by the 12th day. The remaining suppressive antibodies are of IgG-2 class and these increase in concentration until day 8 or 12, or begin to decline between day 8 and day 12. Anti-BALB/c antibodies of IgG-1 class have not yet appeared on day 6, but thereafter appear and increase in concentration. Thus, antibodies of IgG-1 class begin to appear after those of the IgG-2 class and may still be increasing after the IgG-2 class has stopped to increase in concentration, antibody of IgG-1 class is continuing to increase and may even continue to increase after IgF-2 class antibody has begun to decrease in concentration. Thus, the synthesis of IgG-1 class antibody begins later and continues later than that of IgG-2 class. The implications of this sequence for our data on various effects of anti-H-2 antibodies on retention of skin allografts are discussed.