The antigenicity of two closely related sequential polyheptapeptides.

Immunological reactions, both immediate and delayed, were induced in guinea-pigs immunized with two sequential polyheptapeptides, poly-(Leu—Glu—Lys—Ala—Glu—Ser—Gly) and poly-(Leu—Glu—Lys—Ala—Glu—Ala—Gly). The serine-containing polymer was moderately efficient at inducing both types of immune response (7/16 immediate and 12/16 delayed), whereas the polymer containing alanine in place of serine was almost incapable of inducing a humoral response, but invariably induced cell-mediated immunity (1/15 immediate and 15/15 delayed) on primary immunization. The difference is attributed to the lower polarity of the alanine-containing polymer since other evidence exists indicating preferential stimulation of cell-mediated immunity with decreasing polarity of the antigen.