Discrimination between Two Strains (Types) of Herpes Simplex Virus by Various Modifications of the Neutralization Test

Abstract

Two strains (or types) of Herpesvirus hominis, HF and HPF, have been shown to be immunologically related but antigenically distinct by a number of modifications of the neutralization test. Various types of neutralization tests distinguished between the two strains (or types) equally well under the conditions described. The tests differed, however, in ease of performance and capacity for comparative expression of results. The multiplicity neutralization test with 50% plaque reduction and pN value determinations was preferable in most instances. Neutralization of artificial mixtures of the two types of herpesvirus by antiserum to one or the other type was useful in detecting antigenic differences and similarities. Each virus was neutralized in artificial mixtures as though the other was not present. This test merits further consideration in studying viral genetics and mechanisms of cross-neutralization as well as in differentiation of related viruses. In the kinetic neutralization test, antiserum which was either too concentrated or too dilute failed to discriminate between HF and HPF, suggesting the possibility of an optimal serum concentration for most effective discrimination between viruses by an antiserum. Antiserum titers were decreased in tests requiring dilution of virus-antiserum mixtures, a four- to eightfold reduction in titer resulting from dilution to 10^-4. This effect was noted with both homologous virus-antiserum and heterologous virus-antiserum mixtures so that differentiation between the two strains or types could still be accomplished despite dilution. The change in titer upon dilution was thought to be related to the “dilution effect” described in the 1920's and 1930's in which infectious virus was released by dilution of virus-antiserum mixtures.