To investigate the antigenicity of a predicted epitope region of herpes simplex virus gD, peptides comprising the 273-284 sequence have been synthesized and conjugated to a branched polypeptide with polylysine backbone (poly[L-Lys-(DL-Alam)], AK). In order to analyze the effect of the carrier on the solution conformation of the potential peptide-epitopes, three peptides (273-284, 273-281 and 276-284) and their polypeptide conjugates were studied by CD spectroscopy in PBS or in TFE. In immunized BALB/c and CBA mice, the level of peptide-, conjugate- and carrier-specific antibody responses were measured. Conjugates with synthetic polypeptide carrier AK induced epitope-specific IgG responses, accompanied by the appearance of a low level of carrier-specific antibodies. The cross-reactivity pattern of induced antibodies revealed the presence of at least two functionally distinct, overlapping epitopes, the availability of which was influenced by flanking residues at the N-terminus. Preimmunization of BALB/c or CBA mice with the [276-284]-AK conjugate resulted in the production of HSV-specific antibodies and in prolonged survival of animals infected with a lethal dose of herpes simplex virus. The degree of protection was comparable to that of [1-23]-AK conjugate (30).