Key antigenic determinants in regulation of the immune response.

The immune response to beta-galactosidase (beta-D-galactoside galactohydrolase; EC 3.2.1.23)is characterized by a wave of early help followed by a wave of suppression to a subsequent in vitro challenge with galactosidase-fluorescein. A cyanogen bromide peptide of beta-galactosidase, CB2, mimics the suppression seen with the enzyme. It is time dependent, carrier specific, and anti-theta sensitive; however, this suppression is not preceded by a wave of help. It is possible that CB2 cannot stimulate helpers, and is only able to activate suppressor cells. These data indicate that one small region of an antigen, capable of activating suppressors, can nullify the positive effect induced in helper T cells reactive with other epitopes on beta-galactosidase. Key determinants on macromolecules may in this way be influential in regulating the immune response to the entire antigen molecule.