A subset of HLA-DP molecules serve as ligands for the natural cytotoxicity receptor NKp44.

Natural killer (NK) cells can recognize virus-infected and stressed cells1 using activating and inhibitory receptors, many of which interact with HLA class I. Although early studies also suggested a functional impact of HLA class II on NK cell activity2,3, the NK cell receptors that specifically recognize HLA class II molecules have never been identified. We investigated whether two major families of NK cell receptors, killer-cell immunoglobulin-like receptors (KIRs) and natural cytotoxicity receptors (NCRs), contained receptors that bound to HLA class II, and identified a direct interaction between the NK cell receptor NKp44 and a subset of HLA-DP molecules, including HLA-DP401, one of the most frequent class II allotypes in white populations4. Using NKp44ζ+ reporter cells and primary human NKp44+ NK cells, we demonstrated that interactions between NKp44 and HLA-DP401 trigger functional NK cell responses. This interaction between a subset of HLA-DP molecules and NKp44 implicates HLA class II as a component of the innate immune response, much like HLA class I. It also provides a potential mechanism for the described associations between HLA-DP subtypes and several disease outcomes, including hepatitis B virus infection5-7, graft-versus-host disease8 and inflammatory bowel disease9,10.

TLR7-mediated activation of XBP1 correlates with the IFNα production in humans.

The transcription factor X-box binding protein 1 (XBP1) represents a key component of the endoplasmatic reticulum (ER) stress response and is required for the production of several pro-inflammatory cytokines. XBP1 is furthermore essential for the development and survival of plasmacytoid dendritic cells (pDCs), and has recently been suggested to be involved in toll-like receptor (TLR) 2/4 signaling. Activation of TLR7 on pDCs results in an upregulation of pro-inflammatory cytokines, such as type I interferons (IFN-I), and has been implicated in several autoimmune and inflammatory diseases, but the role of XBP1 in this process remains unknown. Here, we show that signaling via TLR7 leads to an upregulation of XBP1 and IFNα-production. XBP1 mRNA expression levels positively correlated with the production of IFNα, while blocking of XBP1 mRNA splicing significantly reduced mRNA transcripts of IFNα. In conclusion, these data suggest a central role of XBP1 in TLR7-induced IFNα production and identify XBP1 as a potential novel therapeutic target in IFNα-driven autoimmune and inflammatory diseases.

Sequence variations in HCV core-derived epitopes alter binding of KIR2DL3 to HLA-C∗03:04 and modulate NK cell function.

BACKGROUND & AIMS: Both natural killer (NK) cells and human leukocyte antigen (HLA)/killer cell immunoglobulin like receptor (KIR) interactions have been shown to play an important role in the control, clearance and progression of hepatitis C virus (HCV) disease. Here we aimed at elucidating the effects of viral peptides derived from HCV on HLA stabilization, changes in KIR binding and primary NK cell function. METHODS: Transporter for antigen presentation-deficient 722.221 cells stably transfected with HLA-C∗03:04 were used to screen 200 overlapping peptides, covering the non-structural protein 3 (NS3) and core protein of HCV genotype 1, for their ability to bind and stabilize HLA-C∗03:04. Binding of KIR2DL3 to the HLA-peptide complex was assessed using a KIR2DL3-IgG fusion construct. Primary NK cells were isolated from healthy donors to investigate the effects of identified peptides on KIR2DL3(+) NK cell function. RESULTS: Thirty-one peptides able to stabilize HLA-C∗03:04 were identified. One 9mer peptide, YIPLVGAPL, resulted in significantly higher KIR2DL3 binding to HLA-C∗03:04(+) 722.221 cells and suppression of primary KIR2DL3(+) NK cell function. Interestingly this sequence exhibited a high frequency of mutations in different HCV genotypes. These genotype-specific peptides showed lower HLA-C∗03:04 stabilization, decreased binding of the inhibitory KIR2DL3 and lower inhibition of NK cell function. CONCLUSIONS: Taken together we show that a viral peptide derived from the core protein of HCV genotype 1 binding to HLA-C∗03:04 results in a sequence-dependent engagement of the inhibitory NK cell receptor KIR2DL3, while the large majority of the remaining 30 HLA-C∗03:04 binding HCV core peptides did not. These data show that sequence variations within HCV can modulate NK cell function, providing potential pathways for viral escape. LAY SUMMARY: We identified a HCV peptide that dampens NK cell responses, and thereby possibly prevents killing of infected cells through this part of the innate immune system. This is facilitated via presentation of the viral peptide on HLA∗03:04 to the inhibitory KIR receptor KIR2DL3 on NK cells. Naturally occurring sequence mutations in the peptide alter these interactions making the inhibition less efficient.

Early antiretroviral therapy favors post-treatment SIV control associated with the expansion of enhanced memory CD8+ T-cells.

HIV remission can be achieved in some people, called post-treatment HIV controllers, after antiretroviral treatment discontinuation. Treatment initiation close to the time of infection was suggested to favor post-treatment control, but the circumstances and mechanisms leading to this outcome remain unclear. Here we evaluate the impact of early (week 4) vs. late (week 24 post-infection) treatment initiation in SIVmac251-infected male cynomolgus macaques receiving 2 years of therapy before analytical treatment interruption. We show that early treatment strongly promotes post-treatment control, which is not related to a lower frequency of infected cells at treatment interruption. Rather, early treatment favors the development of long-term memory CD8+ T cells with enhanced proliferative and SIV suppressive capacity that are able to mediate a robust secondary-like response upon viral rebound. Our model allows us to formally demonstrate a link between treatment initiation during primary infection and the promotion of post-treatment control and provides results that may guide the development of new immunotherapies for HIV remission.

HIV-1 evades a Gag mutation that abrogates killer cell immunoglobulin-like receptor binding and disinhibits natural killer cells in infected individuals with KIR2DL2+/HLA-C*03: 04+ genotype.

: HIV-1 sequence variations impact binding of inhibitory killer cell immunoglobulin-like receptors (KIRs) to human leukocyte antigen class I (HLA-I) molecules modulating natural killer cell function. HIV-1 strains encoding amino acids that mediate binding of inhibitory KIRs might therefore have a selective benefit in individuals expressing the respective KIR/HLA genotypes. Here, we demonstrate that HIV-1 clade C avoids a p24 Gag mutation that abolishes binding of KIR2DL2 to HLA-C03:04 and disinhibits natural killer cells in individual encoding for this genotype.

Peptide-specific engagement of the activating NK cell receptor KIR2DS1.

The activating NK cell receptor KIR2DS1 has been shown to be involved in many disorders including autoimmune diseases, malignancies and pregnancy outcomes. However, the precise ligands and functions of this receptor remain unclear. We aimed to gain a better understanding of the factors involved in the binding of KIR2DS1 and its inhibitory counterpart KIR2DL1 to HLA class I molecules, and the consequences for KIR2DS1+ NK-cell function. A systematic screen that assessed binding to 97 HLA-I proteins confirmed that KIR2DS1-binding was narrowly restricted to HLA-C group 2 complexes, while KIR2DL1 showed a broader binding specificity. Using KIR2DS1ζ+ Jurkat reporter-cells and peptide-pulsed 721.221.TAP1KO-HLA-C*06:02 cells, we identified the synthetic peptide SRGPVHHLL presented by HLA-C*06:02 that strongly engaged KIR2DS1- and KIR2DL1-binding. Functional analysis showed that this HLA-C*06:02-presented peptide can furthermore activate primary KIR2DS1(+) NK cell clones. Thus, we demonstrated peptide-dependent binding of the activating NK cell receptor KIR2DS1, providing new insights into the underlying mechanisms involved in KIR2DS1-related disorders.

Enhanced binding of antibodies generated during chronic HIV infection to mucus component MUC16.

Transmission of HIV across mucosal barriers accounts for the majority of HIV infections worldwide. Thus, efforts aimed at enhancing protective immunity at these sites are a top priority, including increasing virus-specific antibodies (Abs) and antiviral activity at mucosal sites. Mucin proteins, including the largest cell-associated mucin, mucin 16 (MUC16), help form mucus to provide a physical barrier to incoming pathogens. Here, we describe a natural interaction between Abs and MUC16 that is enhanced in specific disease settings such as chronic HIV infection. Binding to MUC16 was independent of IgG subclass, but strongly associated with shorter Ab glycan profiles, with agalactosylated (G0) Abs demonstrating the highest binding to MUC16. Binding of Abs to epithelial cells was diminished following MUC16 knockdown, and the MUC16 N-linked glycans were critical for binding. Further, agalactosylated VRC01 captured HIV more efficiently in MUC16. These data point to a novel opportunity to enrich Abs at mucosal sites by targeting Abs to MUC16 through changes in Fc glycosylation, potentially blocking viral movement and sequestering the virus far from the epithelial border. Thus, next-generation vaccines or monoclonal therapeutics may enhance protective immunity by tuning Ab glycosylation to promote the enrichment of Abs at mucosal barriers.