Pathogenesis of an Infectious Mononucleosis-like Disease Induced by a Murine γ-Herpesvirus: Role for a Viral Superantigen?

The murine γ-herpesvirus 68 has many similarities to EBV, and induces a syndrome comparable to infectious mononucleosis (IM). The frequency of activated CD8⁺ T cells (CD62L^lo) in the peripheral blood increased greater than fourfold by 21 d after infection of C57BL/6J (H-2^b) mice, and remained high for at least a further month. The spectrum of T cell receptor usage was greatly skewed, with as many as 75% of the CD8⁺ T cells in the blood expressing a Vβ4⁺ phenotype. Interestingly, the Vβ4 dominance was also seen, to varying extents, in H-2^k, H-2^d, H-2^u, and H-2^q strains of mice. In addition, although CD4 depletion from day 11 had no effect on the Vβ4 bias of the T cells, the Vβ4⁺CD8⁺ expansion was absent in H-2IA^b–deficient congenic mice. However, the numbers of cycling cells in the CD4 antibody–depleted mice and mice that are CD4 deficient as a consequence of the deletion of MHC class II, were generally lower. The findings suggest that the IM-like disease is driven both by cytokines provided by CD4⁺ T cells and by a viral superantigen presented by MHC class II glycoproteins to Vβ4⁺CD8⁺ T cells.