Coronavirus induction of class I major histocompatibility complex expression in murine astrocytes is virus strain specific

Immunoperoxidase and Immunofluorescent Staining. Cell phenotypes and the number of infected ceUs were determined by immunoperoxidase staining in astrocytes cultured in tissue culture chamber slides. Avidin-biotin immunoperoxidase staining kits (Vectastain; Vector Laboratories Inc., Burlingame, CA) were used according to the manufacturer's instructions as previously described (21) . Cells were infected with virus 1 d after plating and fixed on day 3 or 5 p.i. in acetone/methanol (1:1). The number of positively stained cells in each well was determined in three fields/well at a magnification of 20x and reported as the percentage of the number of total cells in the same fields. Background staining was determined in cells stained in the absence of primary antibody.