Human cytomegalovirus (HCMV) infection promotes a persistent expansion of a function-Keywords: CD94/NKG2C r Cytomegalovirus r Human r NK cells r NKG2C genotype Additional supporting information may be found in the online version of this article at the publisher's web-site

Human CMV (HCMV) infection promotes a variable and persistent expansion of functionally mature NKG2Cbright NK cells. We analyzed NKG2Cbright NK cell responses triggered by Abs from HCMV+ sera against HCMV-infected MRC5 fibroblasts. Specific Abs promoted the degranulation (i.e., CD107a expression) and the production of cytokines (TNF-α and IFN-γ) by a significant fraction of NK cells, exceeding the low natural cytotoxicity against HCMV-infected targets. NK cell–mediated Ab-dependent cell-mediated cytotoxicity was limited by viral Ag availability and HLA class I expression on infected cells early postinfection and increased at late stages, overcoming viral immunoevasion strategies. Moreover, the presence of specific IgG triggered the activation of NK cells against Ab-opsonized cell-free HCMV virions. As compared with NKG2A+ NK cells, a significant proportion of NKG2Cbright NK cells was FcεR γ-chain defective and highly responsive to Ab-driven activation, being particularly efficient in the production of antiviral cytokines, mainly TNF-α. Remarkably, the expansion of NKG2Cbright NK cells in HCMV+ subjects was related to the overall magnitude of TNF-α and IFN-γ cytokine secretion upon Ab-dependent and -independent activation. We show the power and sensitivity of the anti-HCMV response resulting from the cooperation between specific Abs and the NKG2Cbright NK-cell subset. Furthermore, we disclose the proinflammatory potential of NKG2Cbright NK cells, a variable that could influence the individual responses to other pathogens and tumors.

Human cytomegalovirus (HCMV) has been reported to reshape the NK-cell receptor (NKR) distribution, promoting an expansion of CD94/NKG2C + NK and T cells. The role of NK cells in congenital HCMV infection is ill-defined. Here we studied the expression of NKR (i.e., NKG2C, NKG2A, LILRB1, CD161) and the frequency of the NKG2C gene deletion in children with past congenital infection, both symptomatic (n = 15) and asymptomatic (n = 11), including as controls children with postnatal infection (n = 11) and noninfected (n = 20). The expansion of NKG2C + NK cells in HCMV-infected individuals appeared particularly marked and was associated with an increased number of LILRB1 + NK cells in cases with symptomatic congenital infection. Increased numbers of NKG2C + , NKG2A + , and CD161 + T cells were also associated to HCMV infection. The NKG2C deletion frequency was comparable in children with congenital HCMV infection and controls. Remarkably, the homozygous NKG2C +/+ genotype appeared associated with increased absolute numbers of NKG2C + NK cells. Moreover, HCMV-infected NKG2C +/+ children displayed higher absolute numbers of NKG2A + and total NK cells than NKG2C +/− individuals. Our study provides novel insights on the impact of HCMV infection on the homeostasis of the NK-cell compartment in children, revealing a modulatory influence of NKG2C copy number. Eur. J. Immunol. 2012. 42: 3256-3266 Immunity to infection 3257 lifelong latent state, occasionally undergoing reactivation, but may have a pathogenic role in immunodeficient and immunosuppressed patients [1][2][3]. Moreover, HCMV has been associated with atherosclerosis, lymphoproliferative disorders, and glioblastoma, as well as with an accelerated immunosenescence and a shorter lifespan [4][5][6][7]. Vertical transmission of HCMV during pregnancy is considered the most common cause of congenital infection worldwide, affecting ∼0.2-2% of infants and potentially causing fetal lesions [8][9][10]. Though most infected newborns are asymptomatic, ∼10% display a variety of clinical disorders [8,11] potentially leading to important sequelae such as mental retardation and deafness. The type of maternal infection (i.e., primary versus reactivation/reinfection) conditions the risk of congenital infection and the pregnancy stage at which transmission occurs is related to clinical severity [12][13][14][15][16]. Maternal antibodies with neutralizing activity are transferred to the fetus predominantly during the third trimester of gestation and may prevent congenital CMV disease [17]. Among other factors, fetal immune immaturity may determine the outcome of congenital infection [18,19]. An effective defense against HCMV requires the participation of T and NK cells, and the virus has developed different immune evasion strategies [20]. Patients with congenital HCMV infection have been shown to display mature CD8 + T-cell responses [21,22], and an expansion and differentiation of a specific TcR γδ + cell subset has been recently reported [23]. In contrast, information on the role of...

CD94/NKG2C and lack of FcεRγ (FcRγ) expression are considered markers of the adaptive NK cell response to human CMV (HCMV) infection. Despite the fact that FcRγ− and NKG2Cbright NK cells share some phenotypic, epigenetic, and functional features, their relationship remains unclear. To address this issue, a systematic analysis of NKG2Cbright and FcRγ expression was carried out in NK cells from a cohort of healthy young adults (n = 81) considering NKG2C copy number, previously related to the magnitude of NKG2C+ NK cell expansion. NKG2Cbright and FcRγ− NK cells coincided in a subgroup of HCMV+ individuals, pointing to a common host–virus interaction pattern. Even though FcRγ loss was often confined to expanded NKG2Cbright NK cells, both markers appeared occasionally dissociated, consistent with the existence of distinct adaptive NK cell subsets. Remarkably, FcRγ loss was mostly accumulated within the NKG2Cbright subset in NKG2C+/+ subjects, whereas NKG2C−FcRγ− NK cell subpopulations were more frequently detected in NKG2C+/del donors and also in NKG2Cdel/del individuals, independently of activating killer Ig–like receptor expression. The distribution of other NK receptors (i.e., killer Ig–like receptor, LILRB1, or CD57) supported a sequential differentiation from NKG2CbrightFcRγ+ to NKG2CbrightFcRγ− NK cells. Noticeably, NKG2Cbright NK cells produced more TNF-α in response to Ab-dependent activation, regardless of their FcRγ levels. Moreover, the TNF-α response of NKG2C−FcRγ− subpopulations was lower than that of concurrent NKG2CbrightFcRγ− NK cells, further supporting that FcRγ levels and enhanced potential for cytokine production are uncoupled. Overall, our data extend the characterization of adaptive NK cell subsets that differentiate in response to HCMV, supporting a relationship between their distribution and NKG2C copy number.

HSV-1 establishes life-long latency that can result in clinical relapses or in asymptomatic virus shedding. Although virtually all adults have been exposed to HSV-1, the clinical course varies remarkably. Genetic host variability could be related to this clinical diversity. In this study, we analyzed the contribution of gene families in chromosomes 1, 6, 12, and 19, which encode key regulators of the innate and adaptive immunity, in a cohort of 302 individuals. Class I and class II alleles of the HLA system, the copy-number variation of NK cell receptor genes (KIR and NKG2C), the combinations of killer cell Ig-like receptor and their HLA ligands, and CD16A and CD32A allotypes of variable affinity for IgG subclasses were all studied. Although no major susceptibility locus for HSV-1 was identified, our results show that the risk of suffering clinical HSV-1 infection is modified by MHC class I allotypes (B*18, C*15, and the group of alleles encoding A19), the high-affinity receptor/ligand pair KIR2DL2/HLA-C1, and the CD16A-158V/F dimorphism. Conversely, HLA class II and CD32A polymorphisms and NKG2C deletion did not seem to influence the clinical course of herpetic infection. Collectively, these findings support an important role in host defense against herpetic infection for several polymorphic genes implicated in adaptive immunity and in surveillance of its subversion. They confirm the crucial role of cytotoxic cells (CTL and NK) and the contribution of genetic diversity to the clinical course of HSV-1 infection.