The FASEB Journal • Research Communication Soluble ligands for the NKG2D receptor are released during HIV-1 infection and impair NKG2D expression and cytotoxicity of NK cells Giulia Matusali,* Hyppolite Kuekou Tchidjou, † Giuseppe Pontrelli, † Stefania Bernardi, † Gabriella D’Ettorre, ‡ Vincenzo Vullo, ‡ Anna Rita Buonomini,  Massimo Andreoni,  Angela Santoni, § Cristina Cerboni, § and Margherita Doria* ,1 *Laboratory of Immunoinfectivology and † University Department of Pediatrics (DPUO), Bambino Gesù Children’s Hospital, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Rome, Italy; ‡ Department of Public Health and Infectious Diseases and § Department of Molecular Medicine, Istituto Pasteur-Fondazione Cenci Bolognetti, Sapienza University of Rome, Rome, Italy; and  Department of Clinical Infectious Diseases, Tor Vergata University, Rome, Italy ABSTRACT In humans, the interaction of the natural killer group 2 member D (NKG2D)-activating receptor on natural killer (NK) and CD8  T cells with its major histocompatibility complex class I-related chain (MIC) and UL16 binding protein (ULBP) ligands (NKG2DLs) promotes recognition and elimination of stressed cells, such as tumor or infected cells. Here, we investigated the capacity of HIV-1 to modulate NKG2DL expression and escape NGK2D-mediated immunosurveillance. In CD4  T lymphocytes, both cell surface expression and release of MICA, MICB, and ULBP2 were up-regulated >2-fold by HIV-1 infection. In HIV-infected CD4  T lymphocytes or Jurkat T-cell lines, increased shedding of soluble NKG2DLs (sNKG2DLs) was impaired by a matrix metalloproteinase inhibitor (MMPI). Moreover, naive HIV  patients displayed increased plasma sMICA and sULBP2 levels and reduced NKG2D expression on NK and CD8  T cells compared to patients receiving highly active antiretroviral therapy (HAART) or healthy donors. In individual patients, HAART uptake resulted in the drop of sNKG2DL and recovery of NKG2D expression. Finally, sNKG2DLs in patients’ plasma down-regulated NKG2D on NK and CD8  T cells and impaired NKG2D-mediated cytotoxicity of NK cells. Thus, NKG2D detuning by sNKG2DLs may promote HIV-1 immune evasion and compromise host resis- tance to opportunistic infections, but HAART and MMPI have the potential to avoid such immune dysfunction.—Matusali, G., Tchidjou, H. K., Pon- trelli, G., Bernardi, S., D’Ettorre, G., Vullo, V., Buonomini, A. R., Andreoni, M., Santoni, A., Cer- boni, C., Doria, M. Soluble ligands for the NKG2D receptor are released during HIV-1 infection and impair NKG2D expression and cytotoxicity of NK cells. FASEB J. 27, 2440 –2450 (2013). www.fasebj.org Key Words: immune evasion  MICA/B  ULBP  shedding Recent evidence demonstrates that natural killer (NK) cells play an important role in the control of human immunodeficiency virus type 1 (HIV-1) infec- tion (1). NK cells can kill virus-infected and tumor cells without prior antigen exposure and are regu- lated through the balance of signals delivered by two heterogeneous families of inhibitory and activating receptors. The signals elicited by the interaction of the human leukocyte antigen class I (HLA-I) mole- cules on target cells and their cognate inhibitory receptors on NK cells normally dominate to maintain NK cells in a resting state (2). Among the NK cell receptors that deliver activating signals, NK group 2 member D (NKG2D) is one of the most potent. NKG2D is present on the membrane of all NK cells and CD8 + and  T cells and recognizes several 1 Correspondence: Laboratory of Immunoinfectivology, Bambino Gesù Children’s Hospital, Piazza S. Onofrio 4, 00165, Rome, Italy. E-mail: doria@uniroma2.it doi: 10.1096/fj.12-223057 Abbreviations: 7-AAD, 7-aminoactinomycin D; Atv, atazana- vir; CFSE, 5,6-carboxyfluorescein diacetate succinimidyl ester; dpa, days postactivation; ELISA, enzyme-linked immunosor- bent assay; E:T, effector:target; GAM, goat anti-mouse IgG; HAART, highly active antiretroviral therapy; HD, healthy donor; HIV-1, human immunodeficiency virus type 1; HLA, human leukocyte antigen; HLA-I, human leukocyte antigen class I; mAb, monoclonal antibody; MFI, mean fluorescence intensity; MICA, major histocompatibility complex class I-re- lated chain A; MICB, major histocompatibility complex class I-related chain B; MMP, matrix metalloproteinase; MMPI, matrix metalloproteinase inhibitor; n.i., not infected; NK, natural killer; NKG2D, natural killer group 2 member D; NKG2DL, natural killer group 2 member D ligand; PBMC, peripheral blood mononuclear cell; PE, phycoerythrin; PFA, paraformaldehyde; SEB, Staphylococcus aureus enterotoxin B; sMICA, soluble major histocompatibility complex class I-re- lated chain A; sNKG2DL, soluble natural killer group 2 member D ligand; sULBP, soluble UL16 binding protein; ULBP1– 6, UL16 binding protein 1– 6; VSV-G, vesicular sto- matitis virus glycoprotein 2440 0892-6638/13/0027-2440 © FASEB