  According to Jerne's idiotypic network hypothesis, the adaptive immune system
is regulated by interactions between the variable regions of antibodies, B
cells, and T cells.1 The symmetrical immune network theory2,3 is based on
Jerne's hypothesis, and provides a basis for understanding many of the
phenomena of adaptive immunity. The theory includes the postulate that the
repertoire of serum IgG molecules is regulated by T cells, with the result that
IgG molecules express V region determinants that mimic V region determinants
present on suppressor T cells. In this paper we describe rapid binding between
purified murine serum IgG of H-2b and H-2d mice and serum IgG from the same
strain and from MHC-matched mice, but not between serum IgG preparations of
mice with different MHC genes. We interpret this surprising finding in terms of
a model in which IgG molecules are selected to have both anti-anti-(self MHC
class II) and anti-anti-anti-(self MHC class II) specificity.
