Increase of atypical lymphocytes expressing CD4+/CD45RO+ in an infectious mononucleosis-like syndrome associated with hepatitis A virus infection.

Subpopulations of regular and atypical lymphocytes in the peripheral blood of a 24-year-old man with an infectious mononucleosis (IM)-like syndrome associated with hepatitis A virus (HAV) infection were analyzed. The ratio of CD4+ to CD8+ cells was in the normal range (1.19 and 1.23 in the regular and atypical lymphocytes, respectively), with no increase in CD8+ cells. The percentage of CD8+/CD11b- cells was not increased in the atypical lymphocytes. However, CD45RO+ was expressed on 86.3% of CD4+ atypical lymphocytes. The present data suggest that atypical lymphocytes expressing CD4+/CD45RO+ may play the role of helper T cells in the immune system in the development of IM-like syndrome associated with HAV infection.