During the acute phase (1 wk of symptoms or less) of
infectious mononucleosis (IM), 70--80% of circulating
Epstein-Barr virus nuclear antigen (EBNA)-positive cells have differentiated toward plasma cells. Thus the characteristics of the infected cells in the majority of IM patients during early disease are indistinguishable from EBNA-positive
tumor cells of a previously reported child who developed
lymphoma during IM.
IgA and
IgG were the most frequent and
IgM the least frequent
immunoglobulin isotypes detected in EBNA-positive cells. In
acute disease EBNA was present in 5.5--20% of T cell-depleted blood lymphocytes but in the 2nd or 3rd wk of illness the number of EBNA-positive cells sharply decreased to 0.4--1.4%. At the same time the fraction of
antigen-positive cells containing cytoplasmic
immunoglobulins also diminished, suggesting either that differentiation of infected cells was altered during the disease or that nondifferentiated
antigen-positive cells had a survival advantage. Both the high proportion of plasmacytic EBNA-positive cells seen during
acute disease and the apparent loss of differentiation by these cells later in disease may be regulated by host
immunologic factors.
Immunoglobulin-producing EBNA-positive cells may be the source of
heterophile antibodies and other seemingly inappropriate
antibodies usually found in serum during IM; however, increased numbers of noninfected plasma cells were present in some patients and may also be a potential source of these unusual
antibodies.