During childhood, infections with cytomegalovirus (CMV) and Epstein-Barr virus (EBV) can occur in close temporal proximity. interleukin-15 (IL-15) and IL-12p70. Remarkably, EBV infection of peripheral blood mononuclear cells (PBMC) from EBV? CMV+ children increased NKG2C+ NK cell proportions. A similar tendency was seen in cocultures of PBMC with EBV+ lymphoblastoid B-cell lines (LCL) and IL-15. After K562 challenge, NKG2C+ NK cells excelled in regard to degranulation PTC-209 HBr and production of gamma interferon, regardless of whether there was previous coculture with LCL. Taken together, our data suggest that dual latency with these herpesviruses during childhood could contribute to an environment supporting differentiation and maintenance of distinct NK cell populations. This viral imprint may affect subsequent immune responses through altered distributions of effector cells. INTRODUCTION Epstein-Barr virus (EBV) and cytomegalovirus (CMV) are two ubiquitous and persistent herpesviruses commonly contracted during infancy. The course of primary EBV and CMV infection during childhood is typically asymptomatic, whereas infection with EBV during adolescence or adulthood is PTC-209 HBr more severe and often causes infectious mononucleosis (1). After the resolution of primary infection, EBV and CMV become latent, express a highly restricted set of genes, and reside in B and myeloid cells, respectively (1, 2). EBV and CMV can reactivate from latency to produce viral progeny. However, in immunocompetent individuals, no symptoms are evident since reactivation events are tightly controlled by immune cells (1, 2). Natural killer (NK) and CD8+ T (cytotoxic) cells play a key role in the defense against virus-infected cells. CMV, in particular, can drive the differentiation of highly mature (also known as late or terminally differentiated) cytotoxic T cells, phenotypically characterized by the lack of CD28 and expression of CD57 surface markers (3). High expression of CD57 has been linked to elevated lytic granule content in T cells (4, 5). In line with this, highly differentiated CD8+ T cells have a lower activation threshold and a strong capacity to lyse target cells and produce cytokines (3, 6). Differentiation of NK cells is driven by multiple cytokines in addition to cell-cell interactions (7). Recent findings propose that NK cells differentiate further once they enter peripheral sites, i.e., develop to CD56dim cells from the less mature CD56bright cells, whereby they sequentially lose NKG2A, acquire killer immunoglobulin receptors, and upregulate CD57 (7C10). CMV also drives differentiation in NK cells, and NKG2C is one of the PTC-209 HBr NK cell receptors specifically associated with CMV carriage (11C14). Coculture studies have shown that CMV-infected fibroblasts, together with interleukin-15 (IL-15), can induce the expansion of NKG2C+ NK cells (15). Although the precise molecular mechanism for recognition of CMV-infected cells in humans remains unclear, a specific ligand for NKG2C has been recognized as the nonclassical HLA class I molecule HLA-E (16). As for T cells, CD57 expression on NK cells has been suggested to be a marker of highly differentiated memory-like NK cells (17), which is corroborated by findings from a murine CMV infection model (18). Acute viral infections, such as HIV-1 (19) and Rabbit Polyclonal to TEAD1 hantavirus (20), or chronic viruses, such as hepatitis (21), have been associated with NKG2C+ NK cell expansion in CMV-seropositive (CMV+) subjects. No significant role for EBV in driving the terminal differentiation of lymphocytes has been described (11, 22, 23). To our knowledge, however, no studies have yet focused on the possible synergistic role of EBV and CMV coinfection on antiviral effector cell maturation. Notably, earlier studies from our group have suggested a synergistic protective effect of EBV and CMV coinfection against IgE sensitization (24), and distinct modulation of NK cell gamma interferon (IFN-) production capacity by the two viruses (25). This raises the intriguing possibility of interplay of CMV and EBV latency and that this interplay may have a functional imprint on subsequent immune responses early in life. We investigate here the possible effect of EBV coinfection on CMV-driven differentiation of NK and T cells and on functional responses in a cohort of 5-year-old healthy children. We demonstrate that coinfection with EBV and CMV is associated with the highest proportions of NKG2C+ NK cells, as well as memory-like CD57+ NKG2C+ NK cells, compared to single infection with CMV. Further, data herein suggest that the enrichment of NKG2C+ NK cells mediated by EBV coinfection may operate through NK cell interaction with HLA-E+ EBV+ B PTC-209 HBr cells in the.