Differentiation of herpes simplex virus type 1 and type 2 by immunofluorescence: discriminative staining by labelled IgG preparations.

While evaluating herpes simplex virus (HSV) typing by indirect immunofluorescence staining, an undesired specific staining pattern turned out to be a reliable marker for herpes simplex type 1. Cells infected with herpes simplex type 1 displayed clear staining with a FITC-conjugated antiglobulin preparation, also in the absence of herpes simplex-specific antibodies. Using the same conjugate, herpes simplex type-2-infected cells exhibited no fluorescence. The particular type of staining observed was influenced by neither the anatomical site of origin of the virus isolate nor the cell type used for virus preparation. Herpes simplex type 1-specific fluorescence was only obtained with the use of FITC-conjugates possessing anti-IgG activity. Both reliability and specificity of this discriminating procedure as a diagnostic tool has been established by typing 282 virus isolates over a period of 4 years.