Replacement of glycoprotein B gene in the herpes simplex virus type 1 strain ANGpath DNA by that originating from nonpathogenic strain KOS reduces the pathogenicity of recombinant virus.

Herpes simplex virus type-1 (HSV-1) strain ANGpath and its recombinants, in which the 8.1 kbp BamHI G restriction fragment (0.345-0.399) containing the glycoprotein B (gBpath) gene (UL27) or its subfragments-coding either for cytoplasmic or surface domains of gB-had been replaced with the corresponding fragments from nonpathogenic KOS virus DNA (gBKOS), were tested for their pathogenicity for DBA/2 mice and rabbits. The recombinant ANGpath/B6KOS prepared by transferring the 2.7 kbp SstI-SstI subfragment (0.351-0.368) of the BamHI GKOS fragment still had the original sequence of ANGpath DNA coding for the syn3 marker in the cytoplasmic domain of gB and was pathogenic for mice as well as for rabbits. Virological and immunohistological studies in DBA/2 mice infected with the latter pathogenic recombinant and with ANGpath showed the presence of infectious virus and viral antigen at inoculation site (epidermis, subcutaneous connective tissue and striated muscle in the area of right lip), in homolateral trigeminal nerve and ganglion, brain stem, midbrain, thalamic and hypothalamic nuclei. In contrast, nonpathogenic recombinants ANGpath/syn+B6KOS (prepared by transferring the whole BamHI GKOS fragment) and ANGpath/syn+KOS (prepared by transferring the 0.8 kbp BamHI-SstI subfragment of the BamHI GKOS fragment) showed limited haematogenous and neural spread, but no evidence of replication in CNS; thus, their behaviour resembled that of the wild type strain KOS. The recombinant ANGpath/syn+KOS, which was not pathogenic for mice, still remained pathogenic for rabbits, a phenomenon indicating the presence of an additional locus in the gB molecule participating on virulence. Sequencing the 1478 bp SstI-SstI subfragment of the BamHI G(path) fragment (nt 53,348-54,826 of UL segment) showed the presence of at least 3 mutations as compared to the KOS sequence, from which the change of cytosine to thymine at nt 54,251 altered the codon for arginine to that for histidine (amino acid 515) in the gB polypeptide chain.