Bile acids modified by the intestinal microbiota promote colorectal cancer growth by suppressing CD8+ T cell effector functions.

Concentrations of the secondary bile acid, deoxycholic acid (DCA), are aberrantly elevated in colorectal cancer (CRC) patients, but the consequences remain poorly understood. Here, we screened a library of gut microbiota-derived metabolites and identified DCA as a negative regulator for CD8+ T cell effector function. Mechanistically, DCA suppressed CD8+ T cell responses by targeting plasma membrane Ca2+ ATPase (PMCA) to inhibit Ca2+-nuclear factor of activated T cells (NFAT)2 signaling. In CRC patients, CD8+ T cell effector function negatively correlated with both DCA concentration and expression of a bacterial DCA biosynthetic gene. Bacteria harboring DCA biosynthetic genes suppressed CD8+ T cells effector function and promoted tumor growth in mice. This effect was abolished by disrupting bile acid metabolism via bile acid chelation, genetic ablation of bacterial DCA biosynthetic pathway, or specific bacteriophage. Our study demonstrated causation between microbial DCA metabolism and anti-tumor CD8+ T cell response in CRC, suggesting potential directions for anti-tumor therapy.

Gut microbial metabolite facilitates colorectal cancer development via ferroptosis inhibition.

The gut microbiota play a pivotal role in human health. Emerging evidence indicates that gut microbes participate in the progression of tumorigenesis through the generation of carcinogenic metabolites. However, the underlying molecular mechanism is largely unknown. In the present study we show that a tryptophan metabolite derived from Peptostreptococcus anaerobius, trans-3-indoleacrylic acid (IDA), facilitates colorectal carcinogenesis. Mechanistically, IDA acts as an endogenous ligand of an aryl hydrocarbon receptor (AHR) to transcriptionally upregulate the expression of ALDH1A3 (aldehyde dehydrogenase 1 family member A3), which utilizes retinal as a substrate to generate NADH, essential for ferroptosis-suppressor protein 1(FSP1)-mediated synthesis of reduced coenzyme Q10. Loss of AHR or ALDH1A3 largely abrogates IDA-promoted tumour development both in vitro and in vivo. It is interesting that P. anaerobius is significantly enriched in patients with colorectal cancer (CRC). IDA treatment or implantation of P. anaerobius promotes CRC progression in both xenograft model and ApcMin/+ mice. Together, our findings demonstrate that targeting the IDA-AHR-ALDH1A3 axis should be promising for ferroptosis-related CRC treatment.

Elevated triglyceride-glucose index predisposes to the initial episode of peritonitis in chronic peritoneal dialysis patients.

OBJECTIVE: The serum triglyceride-glucose (TyG) index is a marker of inflammation. However, the relationship between TyG index and peritoneal dialysis-related peritonitis (PDRP) is unclear. This study aimed to investigate the potential relationship between the baseline TyG index and the initial episode of PDRP. METHODS: A total of 208 peritoneal dialysis (PD) patients were enrolled from January 1, 2012, to December 31, 2019 and followed up until December 31, 2022. They were divided into 2 groups according to the median TyG. The primary outcome was the occurrence of the initial episode of PDRP while on PD therapy. Kaplan-Meier curves and Cox regression analyses were used to examine the association between them. RESULTS: Eighty-five initial episodes of PDRP were identified. The risk of PDRP was higher in the high-TyG index group (p = 0.030). Multivariate Cox regression analysis showed a higher risk of PDRP in patients with a high TyG index (HR = 1.800, 95% CI 1.511-2.815, p = 0.010). CONCLUSION: The baseline serum TyG index was an independent risk factor for the initial episode of PDRP in chronic PD patients.

G protein-coupled receptor 35 attenuates nonalcoholic steatohepatitis by reprogramming cholesterol homeostasis in hepatocytes.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. Fat accumulation "sensitizes" the liver to insult and leads to nonalcoholic steatohepatitis (NASH). G protein-coupled receptor 35 (GPR35) is involved in metabolic stresses, but its role in NAFLD is unknown. We report that hepatocyte GPR35 mitigates NASH by regulating hepatic cholesterol homeostasis. Specifically, we found that GPR35 overexpression in hepatocytes protected against high-fat/cholesterol/fructose (HFCF) diet-induced steatohepatitis, whereas loss of GPR35 had the opposite effect. Administration of the GPR35 agonist kynurenic acid (Kyna) suppressed HFCF diet-induced steatohepatitis in mice. Kyna/GPR35 induced expression of StAR-related lipid transfer protein 4 (STARD4) through the ERK1/2 signaling pathway, ultimately resulting in hepatic cholesterol esterification and bile acid synthesis (BAS). The overexpression of STARD4 increased the expression of the BAS rate-limiting enzymes cytochrome P450 family 7 subfamily A member 1 (CYP7A1) and CYP8B1, promoting the conversion of cholesterol to bile acid. The protective effect induced by GPR35 overexpression in hepatocytes disappeared in hepatocyte STARD4-knockdown mice. STARD4 overexpression in hepatocytes reversed the aggravation of HFCF diet-induced steatohepatitis caused by the loss of GPR35 expression in hepatocytes in mice. Our findings indicate that the GPR35-STARD4 axis is a promising therapeutic target for NAFLD.

Identification and functional analysis of Dmrt1 gene and the SoxE gene in the sexual development of sea cucumber, Apostichopus japonicus.

Members of the Doublesex and Mab-3-related transcription factor (Dmrt) gene family handle various vital functions in several biological processes, including sex determination/differentiation and gonad development. Dmrt1 and Sox9 (SoxE in invertebrates) exhibit a very conserved interaction function during testis formation in vertebrates. However, the dynamic expression pattern and functional roles of the Dmrt gene family and SoxE have not yet been identified in any echinoderm species. Herein, five members of the Dmrt gene family (Dmrt1, 2, 3a, 3b and 5) and the ancestor SoxE gene were identified from the genome of Apostichopus japonicus. Expression studies of Dmrt family genes and SoxE in different tissues of adult males and females revealed different expression patterns of each gene. Transcription of Dmrt2, Dmrt3a and Dmrt3b was higher expressed in the tube feet and coelomocytes instead of in gonadal tissues. The expression of Dmrt1 was found to be sustained throughout spermatogenesis. Knocking-down of Dmrt1 by means of RNA interference (RNAi) led to the downregulation of SoxE and upregulation of the ovarian regulator foxl2 in the testes. This indicates that Dmrt1 may be a positive regulator of SoxE and may play a role in the development of the testes in the sea cucumber. The expression level of SoxE was higher in the ovaries than in the testes, and knocking down of SoxE by RNAi reduced SoxE and Dmrt1 expression but conversely increased the expression of foxl2 in the testes. In summary, this study indicates that Dmrt1 and SoxE are indispensable for testicular differentiation, and SoxE might play a functional role during ovary differentiation in the sea cucumber.

A2AR limits IL-15-induced generation of CD39+ NK cells with high cytotoxicity.

CD39-mediated inhibition of natural killer (NK) cell activity has been demonstrated, but the characteristics of CD39+ NK cells in humans are not known. We investigated the characteristics of human circulating CD39+ NK cells. In healthy donors, the proportion of circulating CD39+ NK cells in total NK cells was relatively low compared with that of CD39- NK cells. Nonetheless, a higher proportion of CD39+ NK cells expressed CD107a. Similarly, a higher proportion of CD39+ NK cells expressed CD107a in patients with hepatitis B virus or patients with hepatocellular carcinoma. Stimulation with NK-sensitive K562 cells or interleukin (IL)-12/IL-18 activated CD39+ NK cells to express higher levels of CD107a, IFN-γ and TNF-α, relative to CD39- NK cells. Importantly, IL-15 induced the generation of CD39+ NK cells. In contrast, A2A adenosine receptor (A2AR) ligation suppressed the generation of CD39+ NK cells by inhibiting IL-15 signaling. These data for the first time demonstrated that A2AR counteracts IL-15-induced generation of human CD39+ NK cells, which have a stronger cytotoxicity than CD39- NK cells. IL-15-induced human CD39+ NK cells might be better choice for immunotherapy based on adoptive transfer of NK cells.

A modified nutrition risk screening 2002 predicts the risk of death among hospitalized patients with COVID-19.

OBJECTIVES: The aim of this study was to evaluate the ability of a modified Nutrition Risk Screening 2002 (modified NRS) compared with other nutrition screening tools such as NRS 2002, Mini Nutrition Assessment Short Form (MNA-SF), and Malnutrition Universal Screening Tool (MUST) on predicting the risk of death in patients with coronavirus disease 2019 (COVID-19). METHODS: We retrospectively collected data of patients who were admitted to the West campus of Union Hospital, Tongji Medical College, Huazhong University of Science and Technology between January 25th, 2020 to April 24th, 2020. The nutritional status of the patients was assessed by modified NRS, NRS 2002, MNA-SF, and MUST. According to the score of modified NRS, patients were divided into malnutrition risk group (score ≥3) and normal nutrition group (score <3). Clinical characteristics were compared between the two groups. Kaplan meier survival curve was used to analyze the difference of compositing survival rate between the two groups. The predictive efficacy of different nutritional scales on the outcome of death was detected by Receiver operating characteristic (ROC) analysis. RESULTS: The modified NRS, NRS 2002, MNA-SF, and MUST identified malnutrition risk in 71.4%, 57.9%, 73.9%, and 43.4% of the patients, respectively. The patients were divided into malnutrition risk group and normal nutrition group by modified NRS score. Patients in the malnutrition risk group were older (65 y vs. 56 y) and with more severe and critical cases (42.30% vs. 5.20%) and diabetes cases (21.50% vs. 9.80%), worse prognosis (death of 13.80% vs. 0.50%), longer hospital stay (29 days vs. 23 days), lower albumin (31.85 g/L vs. 38.55 g/L) and prealbumin (201.95 mg/L vs. 280.25 mg/L) compared with the normal nutrition group (P were <0.001, respectively). There were more patients with chronic respiratory disease in malnutrition risk group (9.70 vs. 2.10%, P = 0.001). BMI was lower in malnutrition risk group (23.45 kg/m2vs. 24.15 kg/m2, P = 0.017). Kaplan meier survival curve demonstrated that the survival of malnutrition risk group was significantly lower than normal nutrition group (P < 0.001). The area under the ROC curve (AUC) of the modified NRS scale (0.895) outperformed NRS 2002 (0.758), MNA-SF (0.688), and MUST (0.485). The former three scales could predict the risk of death (P were < 0.001), while MUST could not (P = 0.690). CONCLUSIONS: Patients with COVID-19 at risk of malnutrition have a worse prognosis than those with normal nutrition. The modified NRS scale could effectively predict the risk of death among patients with COVID-19.

Kynurenic acid ameliorates NLRP3 inflammasome activation by blocking calcium mobilization via GPR35.

The inflammasome has been linked to diverse inflammatory and metabolic diseases, and tight control of inflammasome activation is necessary to avoid excessive inflammation. Kynurenic acid (KA) is a tryptophan metabolite in the kynurenine pathway. However, the roles and mechanisms of the regulation of inflammasome activation by KA have not yet been fully elucidated. Here, we found that KA suppressed caspase-1 activation and IL-1ß production in macrophages by specifically inhibiting canonical and noncanonical activation of the NLRP3 inflammasome. Mechanistically, KA reduced calcium mobilization through G-protein receptor 35 (GPR35), resulting in reduced mitochondrial damage and decreased mtROS production, thus blocking NLRP3 inflammasome assembly and activation. Importantly, KA prevented lipopolysaccharide-induced systemic inflammation, monosodium urate-induced peritoneal inflammation, and high-fat diet-induced metabolic disorder. Thus, KA ameliorated inflammation and metabolic disorders by blocking calcium mobilization-mediated NLRP3 inflammasome activation via GPR35. Our data reveal a novel mechanism for KA in the modulation of inflammasome activation and suggest that GPR35 might be a promising target for improving NLRP3 inflammasome-associated diseases by regulating calcium mobilization.

Risk of Malnutrition Is Common in Patients with Coronavirus Disease 2019 (COVID-19) in Wuhan, China: A Cross-sectional Study.

BACKGROUND: The coronavirus disease 2019 (COVID-19) has quickly spread across the world. However, the nutritional status of COVID-19 patients has not yet been extensively examined. OBJECTIVES: The aim of this study was to evaluate the nutritional status of COVID-19 patients and to identify factors independently associated with malnutrition risk. METHODS: In this single-center, cross-sectional study, we analyzed data from 760 hospitalized COVID-19 patients between 29 January 2020 and 15 March 2020. Based on the Nutrition Risk Screening (NRS) 2002 score, we divided patients into the normal nutrition group (NRS score <3) and the malnutrition risk group (NRS score ≥3). The associations of age, gender, symptoms, comorbidities, BMI, serum albumin and prealbumin concentrations, disease severity, activities of daily living (ADL) score, and clinical outcomes with malnutrition risk were analyzed. Multivariable logistic regression analysis was used to identify independent factors associated with malnutrition risk. RESULTS: Of patients with COVID-19, 82.6% were at risk of malnutrition. There were statistical differences in the age, incidence of fever, BMI, serum albumin and prealbumin concentrations, ADL score, and disease severity between the 2 groups. Multivariable logistic regression analysis revealed that age ≥65 y (vs. <65 y; OR: 5.40; P < 0.001), serum albumin <35 g/L (vs. ≥35 g/L; OR: 3.61; P < 0.001), serum prealbumin <150 mg/L (vs. ≥150 mg/L; OR: 2.88; P = 0.042), critical cases (vs. moderate cases; OR: 4.46; P < 0.001), ADL score 41-60 (vs. ADL score 100; OR: 4.50; P = 0.012), and ADL score ≤40 (vs. ADL score 100; OR: 9.49; P < 0.001) were significantly associated with the risk of malnutrition in COVID-19 patients. CONCLUSIONS: This study showed that prevalence of malnutrition risk was high in COVID-19 patients. Older age, low serum albumin and prealbumin concentrations, ADL score <60, and disease severity were independent factors associated with malnutrition risk.

RTEF-1 Inhibits Vascular Smooth Muscle Cell Calcification through Regulating Wnt/ß-Catenin Signaling Pathway.

Vascular calcification (VC) is highly prevailing in cardiovascular disease, diabetes mellitus, and chronic kidney disease and, when present, is associated with cardiovascular events and mortality. The osteogenic differentiation of vascular smooth muscle cells (VSMCs) is regarded as the foundation for mediating VC. Related transcriptional enhancer factor (RTEF-1), also named as transcriptional enhanced associate domain (TEAD) 4 or transcriptional enhancer factor-3 (TEF-3), is a nuclear transcriptional factor with a potent effect on cardiovascular diseases, apart from its oncogenic role in the canonical Hippo pathway. However, the role and mechanism of RTEF-1 in VC, particularly in calcification of VSMCs, are poorly understood. Our results showed that RTEF-1 was reduced in calcified VSMCs. RTEF-1 significantly ameliorated ß-glycerophosphate (ß-GP)-induced VSMCs calcification, as detected by alizarin red staining and calcium content assay. Also, RTEF-1 reduced alkaline phosphatase (ALP) activity and decreased expressions of osteoblast markers such as Osteocalcin and Runt-related transcription factor-2 (Runx2), but increased expression of contractile protein, including SM α-actin (α-SMA). Additionally, RTEF-1 inhibited ß-GP-activated Wnt/ß-catenin pathway which plays a critical role in calcification and osteogenic differentiation of VSMCs. Specifically, RTEF-1 reduced the levels of Wnt3a, p-ß-catenin (Ser675), glycogen synthase kinase-3ß (GSK-3ß), and p-GSK-3ß (Ser9), but increased the levels of p-ß-catenin (Ser33/37). Also, RTEF-1 increased the ratio of p-ß-catenin (Ser33/37) to ß-catenin proteins and decreased the ratio of p-GSK-3ß (Ser9) to GSK-3ß protein. LiCl, a Wnt/ß-catenin signaling activator, was observed to reverse the protective effect of RTEF-1 overexpression on VSMCs calcification induced by ß-GP. Accordingly, Dickkopf-1 (Dkk1), a Wnt antagonist, attenuated the role of RTEF-1 deficiency in ß-GP-induced VSMCs calcification. Taken together, we concluded that RTEF-1 ameliorated ß-GP-induced calcification and osteoblastic differentiation of VSMCs by inhibiting Wnt/ß-catenin signaling pathway.

Metabolism of Natural Killer Cells and Other Innate Lymphoid Cells.

Natural killer (NK) cells are the host's first line of defense against tumors and viral infections without prior sensitization. It is increasingly accepted that NK cells belong to the innate lymphoid cell (ILC) family. Other ILCs, comprising ILC1s, ILC2s, ILC3s and lymphoid tissue inducer (LTi) cells, are largely non-cytotoxic, tissue-resident cells, which function to protect local microenvironments against tissue insults and maintain homeostasis. Recently, evidence has accumulated that metabolism supports many aspects of the biology of NK cells and other ILCs, and that metabolic reprogramming regulates their development and function. Here, we outline the current understanding of ILC metabolism, and describe how metabolic processes are affected, and how metabolic defects are coupled to dysfunction of ILCs, in disease settings. Furthermore, we summarize the current and potential directions for immunotherapy involving targeting of ILC metabolism. Finally, we discuss the open questions in the rapidly expanding field of ILC metabolism.

Immunogenic chemotherapy effectively inhibits KRAS-Driven lung cancer.

Immunogenic chemotherapy has been shown to be effective against several cancer types. Here, we identified trametinib as an inducer of immunogenic cell death (ICD), and found that it exerts beneficial antitumor effects if used in combination with interleukin (IL)-12 in a Kras-mutant mouse model of spontaneous lung cancer. Tumor cells treated with trametinib showed the hallmarks of ICD, including cell-surface expression of calreticulin, release of high mobility group box 1 (HMGB1) from the nucleus, and activation of dendritic cells. Tumor-bearing mice treated with both trametinib and IL-12 showed increased infiltration and proliferation of T cells within the tumor, as well as increased effector function of NK cells and T cells, indicating that this therapeutic combination can improve the quality of the immune response. Taken together, our results provide a potential new therapeutic regimen for the treatment of KRAS-mutant lung adenocarcinomas.

Low-Dose Gemcitabine Treatment Enhances Immunogenicity and Natural Killer Cell-Driven Tumor Immunity in Lung Cancer.

Gemcitabine has been used as first-line chemotherapy against lung cancer, but many patients experience cancer recurrence. Activation of anti-tumor immunity in vivo has become an important way to prevent recurrence. Anti-tumor immune responses are often dependent upon the immunogenicity of tumors. In our study, we observed that low-dose gemcitabine treatment enhanced the immunogenicity of lung cancer by increasing the exposure of calreticulin, high mobility group box 1, and upregulating expression of NKG2D ligands. Further studies demonstrated that low-dose gemcitabine treatment increased interferon-γ expression and NK-cell activation in mice. Low-dose gemcitabine treatment was sufficient for inhibiting tumor growth with few side effects in vivo. These data suggest that low-dose gemcitabine-induced immunochemotherapy activated antitumor immunity in immunocompetent patients.

Natural Killer Cells in the Lungs.

The lungs, a special site that is frequently challenged by tumors, pathogens and other environmental insults, are populated by large numbers of innate immune cells. Among these, natural killer (NK) cells are gaining increasing attention. Recent studies have revealed that NK cells are heterogeneous populations consisting of distinct subpopulations with diverse characteristics, some of which are determined by their local tissue microenvironment. Most current information about NK cells comes from studies of NK cells from the peripheral blood of humans and NK cells from the spleen and bone marrow of mice. However, the functions and phenotypes of lung NK cells differ from those of NK cells in other tissues. Here, we provide an overview of human and mouse lung NK cells in the context of homeostasis, pathogenic infections, asthma, chronic obstructive pulmonary disease (COPD) and lung cancer, mainly focusing on their phenotype, function, frequency, and their potential role in pathogenesis or immune defense. A comprehensive understanding of the biology of NK cells in the lungs will aid the development of NK cell-based immunotherapies for the treatment of lung diseases.

Author Correction: Memory formation and long-term maintenance of IL-7Rα+ ILC1s via a lymph node-liver axis.

The original version of this Article contained errors in Figs. 1 and 6. In Fig. 1c, the label 'CD49a+IL-7Rα+ ILC1' incorrectly read 'CD49a+IL-7Rα- ILC1'. In Fig. 6b, the label 'LNx (e)/ILN-deficient mice (c)' incorrectly read 'LNx (c)/ILN-deficient mice (e)'. These errors have now been corrected in both the PDF and HTML versions of the Article.

Memory formation and long-term maintenance of IL-7Rα+ ILC1s via a lymph node-liver axis.

Natural killer (NK) cells are reported to have immunological memory, with CD49a+ liver-resident NK cells shown to confer hapten-specific memory responses, but how this memory is induced or maintained is unclear. Here we show that memory type I innate lymphoid cells (ILC1s), which express IL-7Rα, are generated in the lymph nodes (LNs) and require IL-7R signaling to maintain their longevity in the liver. Hapten sensitization initiates CXCR3-dependent recruitment of IL-7Rα+ ILC1s into skin-draining LNs, where they are primed and acquire hapten-specific memory potential. Memory IL-7Rα+ ILC1s then exit draining LNs and are preferentially recruited, via CXCR6, to reside in the liver. Moreover, long-term blockade of IL-7R signaling significantly reduces ILC1-mediated memory responses. Thus, our results identify a memory IL-7Rα+ ILC1 population and reveal a LN-liver axis that is essential for ILC1 memory generation and long-term maintenance.

Dysfunction of Natural Killer Cells by FBP1-Induced Inhibition of Glycolysis during Lung Cancer Progression.

Natural killer (NK) cells are effector lymphocytes with pivotal roles in the resistance against various tumors; dysfunction of NK cells often results in advanced tumor progression. Tumors develop in three stages comprising initiation, promotion, and progression, but little is known about the interrelationships between NK cells and tumor cells at different stages of tumor development. Here, we demonstrated that NK cells prevented tumor initiation potently but did not prevent tumor promotion or tumor progression in Kras-driven lung cancer. Moreover, loss of the antitumor effect in NK cells was closely associated with their dysfunctional state during tumor promotion and progression. Mechanistically, aberrant fructose-1,6-bisphosphatase (FBP1) expression in NK cells elicited their dysfunction by inhibiting glycolysis and impairing viability. Thus, our results show dynamic alterations of NK cells during tumor development and uncover a novel mechanism involved in NK cell dysfunction, suggesting potential directions for NK cell-based cancer immunotherapy involving FBP1 targeting.

Detection and Characterization of Hepatitis E Virus in Goats at Slaughterhouse in Tai'an Region, China.

BACKGROUND: Hepatitis E virus (HEV) is a significant pathogen of viral hepatitis and can be transmitted through fecal-oral route. Epidemiological data concerning HEV in goats, however, are relatively sparse to date. Here, the prevalence and characteristics of HEV isolated from goats at slaughterhouse were investigated in Tai'an region, China. METHODS: Anti-HEV immunoglobulin G (IgG) in blood samples and HEV RNA in the liver samples were determined by using an enzyme-linked immunosorbent assay (ELISA) and a nested reverse transcription polymerase chain reaction (RT-PCR), respectively. In addition, partial nucleotide sequences of open reading frame 2 (ORF-2) of HEV isolates were analyzed. RESULTS: Fifty goat blood samples (46.7%, 50/120) were masculine for anti-HEV IgG. HEV RNA was detected in 2 liver samples (4.0%, 2/50) and belonged to genotype 4 subtype 4 h, with high identity (91.2-93%) with cow HEV strains detected in the same province, China. CONCLUSIONS: These findings demonstrated that goats may be an important reservoir for HEV and can become a major source of HEV infection in humans via food chain.

Cytoplasm-Translocated Ku70/80 Complex Sensing of HBV DNA Induces Hepatitis-Associated Chemokine Secretion.

Chronic hepatitis B virus (HBV) infection remains a serious disease, mainly due to its severe pathological consequences, which are difficult to cure using current therapies. When the immune system responds to hepatocytes experiencing rapid HBV replication, effector cells (such as HBV-specific CD8+ T cells, NK cells, NKT cells, and other subtypes of immune cells) infiltrate the liver and cause hepatitis. However, the precise recruitment of these cells remains unclear. In the present study, we found that the cytoplasm-translocated Ku70/80 complex in liver-derived cells sensed cytosolic HBV DNA and promoted hepatitis-associated chemokine secretion. Upon sensing HBV DNA, DNA-dependent protein kinase catalytic subunit and PARP1 were assembled. Then, IRF1 was activated and translocated into the nucleus, which upregulated CCL3 and CCL5 expression. Because CCR5, a major chemokine receptor for CCL3 and CCL5, is known to be critical in hepatitis B, Ku70/80 sensing of HBV DNA likely plays a critical role in immune cell recruitment in response to HBV infection.