Antigenic and genetic differentiation of the two putative types of human herpes virus 6.

Ten human herpes virus 6 (HHV-6) strains from different origins were studied using reactivity to monoclonal antibodies and polymerase chain reaction analysis. Using immunofluorescence and neutralization assays, two monoclonal antibodies gave a positive reaction with the ten strains while three others only reacted with a fraction of these strains. This differential reactivity permitted segregation of the ten strains into two non-overlapping antigenic groups, designated as I and II. DNA was amplified from two regions of HHV-6 genome corresponding to the putative large tegument protein (LTP) gene and major capsid protein (MCP) gene, respectively. The restriction analysis of amplified products using HindIII for LTP and HaeII for MCP showed identical patterns among the strains belonging to the same antigenic group while BglII, TaqI and ClaI provided distinct patterns among group II strains. The nucleotide sequence of amplified products was determined and homology was found to be equal to or greater than 99% within each group whereas it was 96% between both groups. The number of amino-acid changes was higher when comparing two strains of different groups than when comparing two strains of the same group. The converging results of antigenic and genetic analyses led us to consider HHV-6 groups I and II as two distinct types of HHV-6 species.