Titers of antibody to KSHV were determined by immunofluorescence assay (IFA) using PMA-stimulated TY-1, a KSHV-infected primary effusion lymphoma cell line [31]. TY-1 cells were stimulated with PMA for 48 h and smeared on slides. After acetone fixation, the smear slides were stored at −25 °C. Serum, NW, or saliva were diluted by dilution factors 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 for IgA, and 50, 100, 200, 400, 800, 1600, 3200, 6400, 12,800, and 25,600 for IgG 5-FU concentration in Block Ace (Snow-Brand, Tokyo, Japan). Diluted samples were applied on the smear slides, and incubated at room temperature for 1 h. After washing with PBS, the slides were

reacted with FITC-conjugated anti-mouse IgG or IgA antibody (BD Bioscience) for 30 min. Followed by washing and mounting, the slides were observed with a fluorescence microscope. Antibody titers were determined at the dilution of positive signals. For identification of immunogens in KSHV-immunized mice, dual-labeled IFA was performed.

The mouse serum and anti-KSHV ORF K8, K8.1, ORF26, ORF59, ORF65, or ORF73 (LANA-1) rabbit polyclonal antibodies were reacted with the smear slides as the primary antibodies [7]. After washing, the slides were reacted with Alexa 488-conjugated anti-mouse IgG antibody and Alexa 568-conjugated anti-rabbit IgG antibody (Molecular Probe, Eugene, OR) as the secondary antibodies. After washing Venetoclax and mounting, the slides were observed with a confocal microscope (FV-1000, Olympus, Tokyo, Japan). One hundred μl of 1000× diluted serum or 10× diluted NW or saliva were incubated with 106 copies of rKSHV.219, which contained about 100 infectious units, in DMEM in tubes at 37 °C for 2 h [28]. After the incubation, 100 μl of the virus solution was added to human embryonic kidney 293 cells (293 cells) in a 96-well plate. The plate was centrifuged for a short time at a low speed, and incubated for 2 h in a CO2 incubator. After removing the supernatant, fresh media was added, and the cells were cultured at 37 °C.

Five days after infection, the number until of GFP+ cells in each well was counted under a fluorescence microscope. Glutathione S-transferase (GST)-fusion proteins of K8, K8.1, ORF26, ORF59, ORF65, and ORF73 were synthesized as described previously [4]. Fifty nanograms of each GST-fusion protein was applied to western blotting. Since molecular sizes of these GST-fusion proteins range 41–60 kDa, 50 ng protein is corresponding to 0.8–1.2 pmol. The serum from mice and anti-GST rabbit polyclonal antibody were used as the primary antibodies. Anti-mouse or rabbit IgG antibodies (BD Bioscience) were used as the secondary antibodies; signals were detected with a chemiluminescence solution (Westdura, Pierce Biotechnology, Rockford, IL). Student’s t-test was applied for the comparison of mRNA levels and the KSHV neutralization assay.