Figure 1

MNV-1, but not MNV-3, induces B cells to upregulate antigen presentation molecules. (a) Duplicate wells of M12 cells were inoculated with mock inoculum (black bars), MNV-1 (gray bars), or MNV-3 (white bars) at MOI 5. At 2 d.p.i., cell were stained with antibodies to MHC I, MHC II, CD40, CD80, and CD86. Flow cytometry was carried out as described in the Methods and isotype control antibodies were used to set gates. The experiment was repeated three times and data from all experimental replicates were averaged. Statistical comparisons were made between mock and each virus strain; and MNV-1 and MNV-3. (b) The same experiment described for panel A was repeated two additional times, performing parallel M12 and RAW 264.7 cell infections. RAW 264.7 cells were stained for surface markers at 1 d.p.i. because of the faster viral replication kinetics in this cell line. Data for MHC I levels are presented as the fold-difference in expression on infected cells compared to mock-inoculated cells. The same trend (increased expression on MNV-1-infected M12 cells and MNV-3-infected RAW 264.7 cells) was observed for MHC II, CD40, CD80, and CD86 as well (data not shown). (c) Groups (n=2) of B6 mice were mock-inoculated (black bars) or infected p.o. with 10⁷ TCID₅₀ units MNV-1 (gray bars) or MNV-3 (white bars). At 2 d.p.i., Peyer’s patches were dissected, pooled for each mouse, and single cell suspensions were generated. Cells were stained for CD19, MHC I, MHC II, CD40, CD80, and CD86 and assessed by flow cytometry. Data are reported as the percentage of CD19⁺ cells expressing each antigen presentation molecule. The experiment was repeated three times and data from all experimental replicates were averaged. Statistical comparisons were made between mock and each virus strain; and MNV-1 and MNV-3. (d) Groups of B6 (black bars), B2M^−/− (gray bars), and MHC II^−/− (white bars) mice were infected p.o. with 10⁷ TCID₅₀ units MNV-1 or MNV-3, as indicated on the x axis. At 3 d.p.i., the indicated tissues were dissected and viral titers were determined by plaque assay. The data are reported as pfu per gram of tissue and the data for all mice per group (n=6–8 mice over three experiments) are averaged. Dashed lines indicate the limit of detection for each tissue. B6 mice were compared with B2M^−/− and MHC II^−/− strains, and B2M^−/− and MHC II^−/− were compared with each other, for statistical purposes for each virus strain. d.p.i., days post infection; MOI, multiplicity of infection; p.o., perorally.

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