The humoral immune response against α(1→3) dextran (Dex) in BALB/c mice is characterized
by the formation of predominantly IgM antibodies bearing the J558 idiotype. IgG antibodies
do not appear in euthymic mice. In athymic animals however, the response proceeds to
a vigorous IgG production. In euthymic mice formation of IgG is suppressed by J558 idiotype-
specific regulatory T cells recognizing in association with I-Ed and in cognate T/B interaction
the VH CDR3 derived peptide of the J558 idiotpye. Only B-2 lymphocytes produce
IgG whereas B-1 cells do not participate in the production of this Ig class. Using a novel synthetic
all α(1→3)-D-gluco configurated tetrasaccharide the Dex-specific B cells can for the
first time be analyzed in FACS. In experiments using this newly designed low molecular Dex
no signs of B cell apoptosis can be found. This demonstrates a true silencing of persisting Bγ
memory cells and supports previous by adoptive transfer experiments. In this suppression an
involvement of CD28/B7–1 interaction can be demonstrated which is a necessary costimulatory
suppression signal in addition to the cognate TCR/peptide-I-Ed interaction between J558
Id-specific T cells and J558 idiotype beating B cells. This results in an activation of 178–4 Ts
cells, leading to an overall suppression of the Dex-specific IgG isotype production on the one
hand and on the other hand provides a signal for the survival and clonal expansion of J558
Id-positive B cells.
