FXR mediates T cell-intrinsic responses to reduced feeding during infection.

Reduced nutrient intake is a widely conserved manifestation of sickness behavior with poorly characterized effects on adaptive immune responses. During infectious challenges, naive T cells encountering their cognate antigen become activated and differentiate into highly proliferative effector T cells. Despite their evident metabolic shift upon activation, it remains unclear how effector T cells respond to changes in nutrient availability in vivo. Here, we show that spontaneous or imposed feeding reduction during infection decreases the numbers of splenic lymphocytes. Effector T cells showed cell-intrinsic responses dependent on the nuclear receptor Farnesoid X Receptor (FXR). Deletion of FXR in T cells prevented starvation-induced loss of lymphocytes and increased effector T cell fitness in nutrient-limiting conditions, but imparted greater weight loss to the host. FXR deficiency increased the contribution of glutamine and fatty acids toward respiration and enhanced cell survival under low-glucose conditions. Provision of glucose during anorexia of infection rescued effector T cells, suggesting that this sugar is a limiting nutrient for activated lymphocytes and that alternative fuel usage may affect cell survival in starved animals. Altogether, we identified a mechanism by which the host scales immune responses according to food intake, featuring FXR as a T cell-intrinsic sensor.

Trends and Health Care Outcomes Among Living Liver Donors: Are We Ready to Expand the Donor Pool With Living Liver Donations?

We studied the trends and various outcomes, including the readmission rates, health care utilization, and complications among living liver donors (LLDs) in the United States. We queried the National Database for data from 2010 to 2017 for all LLDs. The primary outcomes were 30-day and 90-day readmission rates. The secondary outcomes included health care use (length of stay [LOS], cost of care), index admission, and calendar-year mortality. Logistic regression models were fit for various outcomes. A total of 1316 LLDs underwent hepatectomy during the study period. The median donor age was 35.0 years (interquartile range, 27.4-43.6), and donors were predominantly women (54.2%). The trend of LLD surgeries remained stable at large medical centers (85.3%). The 30-day and 90-day readmission rates were low at 5% and 5.9%, respectively. Older age (50 years and older; 8%; confidence interval [CI], 0.6%-15.9%; P = 0.03) and hepatectomy at small to medium-sized hospitals were associated with increased index LOS (13.4%; 95% CI, 3.1%-24.7%; P = 0.01). Moreover, older age of donor (-11.3%; 95% CI, -20.3% to -1.4%; P = 0.03), Elixhauser score ≥3 (17%; 95% CI, 1.2%-35.3%; P = 0.03), and Medicaid insurance (24.5%; 95% CI, 1.2%-53.1%; P = 0.04) were also associated with increased cost. The overall rate of any complications during index admission was 42.8%. Male sex (odds ratio [OR], 1.63; 95% CI, 1.19-2.23) was an independent predictor of post-LLD complications. There was no index admission or calendar-year mortality reported during the study period. This is the largest national report of LLDs to date, showing that the trend of LLD surgeries is stable in the United States. With established safety, fewer complications, and less health care utilization, LLDs can be a potential source of continuation of liver transplantation in the context of changing liver allocation policies in the United States.

Cannabis use may reduce healthcare utilization and improve hospital outcomes in patients with cirrhosis.

INTRODUCTION AND OBJECTIVES: Previous studies reveal conflicting data on the effect of cannabis use in patients with cirrhosis. This research evaluates the impact of cannabis on hepatic decompensation, health care utilization, and mortality in patients with cirrhosis. MATERIAL AND METHODS: A retrospective analysis of the State Inpatient Database (SID) was performed evaluating patients from Colorado and Washington in 2011 to represent pre-cannabis legalization and 2015 to represent post-cannabis legalization. Multivariable analysis was performed to study the impact of cannabis on the rate of admissions with hepatic decompensations, healthcare utilization, and mortality in patients with cirrhosis. RESULTS: Cannabis use was detected in 370 (2.1%) of 17,520 cirrhotics admitted in 2011 and in 1162 (5.3%) of 21,917 cirrhotics in 2015 (p-value <0.001). On multivariable analysis, cirrhotics utilizing cannabis after its legalization experienced a decreased rate of admissions related to hepatorenal syndrome (Odds Ratio (OR): 0.51; 95% Confidence Interval (CI): 0.34-0.78) and ascites (OR: 0.73; 95% CI: 0.63-0.84). Cirrhotics with an etiology of disease other than alcohol and hepatitis C had a higher risk of admission for hepatic encephalopathy if they utilized cannabis [OR: 1.57; 95% CI: 1.16-2.13]. Decreased length of stay (-1.15 days; 95% CI: -1.62, -0.68), total charges (-$15,852; 95% CI: -$21,009, -$10,694), and inpatient mortality (OR: 0.68; 95% CI: 0.51-0.91) were also observed in cirrhotics utilizing cannabis after legalization compared to cirrhotics not utilizing cannabis or utilizing cannabis prior to legalization. CONCLUSION: Cannabis use in patients with cirrhosis resulted in mixed outcomes regarding hospital admissions with hepatic decompensation. A trend towards decreased hospital utilization and mortality was noted in cannabis users after legalization. These observations need to be confirmed with a longitudinal randomized study.

Outcomes of hepatitis C virus seropositive donors to hepatitis C virus seronegative liver recipients: A large single center analysis.

INTRODUCTION AND OBJECTIVES: The success of direct-acting antivirals (DAA) has transformed the management of hepatitis C virus (HCV) infection and has led to the expansion of the deceased donor organ pool for liver transplantation. MATERIAL AND METHODS: We present a single center retrospective review of liver transplantations performed on HCV-seronegative recipients from HCV-seropositive organs from 11/2017 to 05/2020. HCV nucleic acid testing (NAT) was performed on HCV-seropositive donors to assess active HCV infection. RESULTS: 42 HCV-seronegative recipients underwent a liver transplant from a HCV-seropositive donor, including 21 NAT negative (20 liver, 1 simultaneous liver kidney transplant) and 21 NAT positive liver transplants. Two (9.5%) HCV antibody positive/NAT negative recipients developed HCV viremia and achieved sustained virologic response with DAA therapy. The remaining patients with available data (19 patients) remained polymerase chain reaction (PCR) negative at 6 months. 20 (95%) of HCV antibody positive/NAT positive recipients had a confirmed HCV viremia. 100% of patients with available data (15 patients) achieved SVR. Observed events include 1 mortality and graft loss and equivalent rates of post-transplant complications between NAT positive and NAT negative recipients. CONCLUSIONS: HCV-seropositive organs can be safely transplanted into HCV-seronegative patients with minimal complications post-transplant.

Anti-CD40 antibody 2C10 binds to a conformational epitope at the CD40-CD154 interface that is conserved among primate species.

The antagonistic anti-CD40 antibody, 2C10, and its recombinant primate derivative, 2C10R4, are potent immunosuppressive antibodies whose utility in allo- and xenotransplantation have been demonstrated in nonhuman primate studies. In this study, we defined the 2C10 binding epitope and found only slight differences in affinity of 2C10 for CD40 derived from four primate species. Staining of truncation mutants mapped the 2C10 binding epitope to the N-terminal portion of CD40. Alanine scanning mutagenesis of the first 60 residues in the CD40 ectodomain highlighted key amino acids important for binding of 2C10 and for binding of the noncross-blocking anti-CD40 antibodies 3A8 and 5D12. All four 2C10-binding residues defined by mutagenesis clustered near the membrane-distal tip of CD40 and partially overlap the CD154 binding surface. In contrast, the overlapping 3A8 and 5D12 epitopes map to an opposing surface away from the CD154 binding domain. This biochemical characterization of 2C10 confirms the validity of nonhuman primate studies in the translation of this therapeutic antibody and provides insight its mechanism of action.

Validation of Risk Score in Predicting Early Readmissions in Decompensated Cirrhotic Patients: A Model Based on the Administrative Database.

Early readmission in patients with decompensated liver cirrhosis leads to an enormous burden on health care use. A retrospective cohort study using the 2013 and 2014 Nationwide Readmission Database (NRD) was conducted. Patients with a diagnoses of cirrhosis and at least one feature of decompensation were included. The primary outcome was to develop a validated risk model for early readmission. Secondary outcomes were to study the 30-day all-cause readmission rate and the most common reasons for readmission. A multivariable logistic regression model was fit to identify predictors of readmissions. Finally, a risk model, the Mumtaz readmission risk score, was developed for prediction of 30-day readmission based on the 2013 NRD and validated on the 2014 NRD. A total of 123,011 patients were included. The 30-day readmission rate was 27%, with 79.6% of patients readmitted with liver-related diagnoses. Age <65 years; Medicare or Medicaid insurance; nonalcoholic etiology of cirrhosis; ≥3 Elixhauser score; presence of hepatic encephalopathy, ascites, variceal bleeding, hepatocellular carcinoma, paracentesis, or hemodialysis; and discharge against medical advice were independent predictors of 30-day readmission. This validated model enabled patients with decompensated cirrhosis to be stratified into groups with low (<20%), medium, (20%-30%), and high (>30%) risk of 30-day readmissions. Conclusion: One third of patients with decompensated cirrhosis are readmitted within 30 days of discharge. The use of a simple risk scoring model with high generalizability, based on demographics, clinical features, and interventions, can bring refinement to the prediction of 30-day readmission in high-risk patients; the Mumtaz readmission risk score highlights the need for targeted interventions in order to decrease rates of readmission within this population.

Management of hepatic hydrothorax and effect on length of stay, mortality, cost, and 30-day hospital readmission.

BACKGROUND AND AIM: Cirrhosis-related complications are associated with high inpatient mortality, cost, and length of stay. There is a lack of multi-centered studies on interventions for hepatic hydrothorax and its impact on patient outcomes. The aim of this study was to determine the effect of performing thoracentesis for hepatic hydrothorax on hospital length of stay, mortality, cost, and 30-day readmission. METHODS: A retrospective analysis of the Nationwide Inpatient Sample between 2002 and 2013 and Nationwide Readmission Database during 2013 was performed including patients with a primary diagnosis of hydrothorax or pleural effusion and a secondary diagnosis of cirrhosis based on International Classification of Disease 9 codes. Univariate and multivariate analyses were performed to determine the effect of thoracentesis on patient outcomes during their hospital stay. RESULTS: Of the 37 443 patients included from the Nationwide Inpatient Sample, 26 889 (72%) patients underwent thoracentesis. Thoracentesis was associated with a longer length of stay (4.56 days, 95% confidence interval [CI]: 2.40-6.72) and higher total cost ($9449, 95% CI: 3706-15 191). There was no significant difference in inpatient mortality between patients who underwent thoracentesis compared with those who did not. Of the 2371 patients included from the Nationwide Readmission Database, 870 (33%) were readmitted within 30 days. Thoracentesis was not a predictor of readmission; however, transjugular intrahepatic portosystemic shunt (odds ratio: 4.89, 95% CI: 1.17-20.39) and length of stay (odds ratio: 1.02, 95% CI: 1.001-1.05) on index admission were predictors of readmission. CONCLUSION: When considering treatment for hepatic hydrothorax, many factors should contribute to determining the best intervention. While performing thoracentesis may provide immediate relief to symptomatic patients, it should not be considered a long-term intervention given that it increases hospital cost, was associated with longer length of stays, and did not improve mortality.

A validated risk model for prediction of early readmission in patients with hepatic encephalopathy.

INTRODUCTION AND AIM: Hepatic encephalopathy (HE) is a common complication in cirrhotics and is associated with an increased healthcare burden. Our aim was to study independent predictors of 30-day readmission and develop a readmission risk model in patients with HE. Secondary aims included studying readmission rates, cost, and the impact of readmission on mortality. MATERIALS AND METHODS: We utilized the 2013 Nationwide Readmission Database (NRD) for hospitalized patients with HE. A risk assessment model based on index hospitalization variables for predicting 30-day readmission was developed using multivariate logistic regression and validated with the 2014 NRD. Patients were stratified into Low Risk and High Risk groups. Cox regression models were fit to identify predictors of calendar-year mortality. RESULTS: Of 24,473 cirrhosis patients hospitalized with HE, 32.4% were readmitted within 30 days. Predictors of readmission included presence of ascites (OR: 1.19; 95% CI: 1.06-1.33), receiving paracentesis (OR: 1.43; 95% CI: 1.26-1.62) and acute kidney injury (OR: 1.11; 95% CI: 1.00-1.22). Our validated model stratified patients into Low Risk and High Risk of 30-day readmissions (29% and 40%, respectively). The cost of the first readmission was higher than index admission in the 30-day readmission cohort ($14,198 vs. $10,386; p-value <0.001). Thirty-day readmission was the strongest predictor of calendar-year mortality (HR: 4.03; 95% CI: 3.49-4.65). CONCLUSIONS: Nearly one-third of patients with HE were readmitted within 30 days, and early readmission adversely impacted healthcare utilization and calendar-year mortality. With our proposed simple risk assessment model, patients at high risk for early readmissions can be identified to potentially avert poor outcomes.

Rotational Thromboelastometry or Conventional Coagulation Tests in Liver Transplantation: Comparing Blood Loss, Transfusions, and Cost.

INTRODUCTION: Orthotopic liver transplantation (OLT) can be associated with significant bleeding requiring multiple blood product transfusions. Rotational thromboelastometry (ROTEM) is a point-of-care device that has been used to monitor coagulation during OLT. Whether it reduces blood loss/transfusions during OLT remains controversial. MATERIALS AND METHODS: We aim to compare ROTEM with conventional coagulation tests (aPTT, PT, INR, platelet count, fibrinogen) to guide transfusion of platelets, cryoprecipitate, and fresh frozen plasma (FFP) during OLT over 3 years. Thirty-four patients who had transfusions guided by ROTEM were compared to 34 controls who received transfusions guided by conventional coagulation tests (CCT). Intraoperative blood loss, type/ amount of blood products transfused, and direct costs were compared between the two groups. RESULTS: The ROTEM group had significantly less intra-operative blood loss (2.0 vs. 3.0 L, p = 0.04) and fresh frozen plasma (FFP) transfusion (4 units vs. 6.5 units, p = 0.015) compared to the CCT group (2.0L vs. 3.0L, p = 0.04). However, total number of patients transfused cryoprecipitate was increased in ROTEM (n = 25;73%) as compared to CCT (n = 19; 56%), p = 0.033. The direct cost of blood products plus testing was reduced in the ROTEM group ($113,142.89 vs. $127,814.77). CONCLUSION: In conclusion implementation of a ROTEM-guided transfusion algorithm resulted in a reduction in intra-operative blood loss, FFP transfusion and a decrease in direct cost during OLT. ROTEM is a useful and safe point of care device in OLT setting.

An indeterminate nodule in the cirrhotic liver discovered by surveillance imaging is a prelude to malignancy.

BACKGROUND: Surveillance imaging often shows indeterminate lesions in the cirrhotic liver, which may represent early hepatocellular carcinoma (HCC), dysplastic or regenerative nodules, or vascular shunts. The risk of HCC after identification of an indeterminate nodule is not well described. METHODS: We identified 252 patients with cirrhosis and at least one indeterminate nodule discovered on surveillance imaging over a 4-year period. The incidence of HCC development within 2 years of nodule identification was measured along with baseline risk factors associated with developing HCC. RESULTS: The incidence of HCC in this population was 21% (53 of 252), and risk factors associated with HCC included chronic viral hepatitis, male gender, and low platelet count. The median time from identification of an indeterminate nodule to diagnosis of HCC was 2.7 months. Patients with indeterminate nodules who developed HCC were more likely have to have an indeterminate nodule with arterial enhancement. CONCLUSIONS: The 2-year incidence of HCC in the setting of cirrhosis and an indeterminate nodule discovered by surveillance imaging may be as high as one in five persons. Early follow-up imaging, biopsy, or empiric treatment should be considered for those at higher risk. Further, this population is well suited for early detection biomarker and chemoprevention studies.

Inflammatory markers are associated with outcome in patients with unresectable hepatocellular carcinoma undergoing transarterial chemoembolization.

BACKGROUND: The serum neutrophil-lymphocyte ratio (NLR) is associated with outcomes in several solid organ cancers, including hepatocellular carcinoma (HCC). METHODS: We reviewed our experience in patients with HCC who underwent transarterial chemoembolization (TACE) as the initial treatment. Serum complete blood counts were used to calculate the NLR before and after TACE. The Kaplan-Meier method was used to determine survival and significant differences between groups by the log-rank test. RESULTS: There were 103 patients identified who underwent TACE for HCC. The median age was 60.5 years. Median overall survival was 12.6 (95% confidence interval 8.3-17) months. Median survival in patients with a high preprocedural NLR was 4.2 months compared to 15 months in those with a normal NLR (p = 0.021). In those whose NLR either rose 1 month after treatment or remained elevated, survival was worse compared to those who normalized or remained normal (18.6 vs. 10.6 months, p = 0.026). The same was true at 6 months (21.3 vs. 9.5 months, p = 0.002). An unresponsive NLR was associated with very poor outcome (median survival 3.7 months). Multivariate analysis of clinicopathologic factors showed that presence of extrahepatic disease and high NLR were independent factors associated with worse survival. CONCLUSIONS: Our study demonstrates that periprocedural trends of serum NLR are associated with outcome in unresectable HCC undergoing TACE. Serum NLR is easy to calculate from a routine complete blood count with differential. Along with liver function, serum NLR may be helpful to clinicians in providing prognostic information and monitoring response to therapy.

Hepatic preservation injury: severity of hepatitis C recurrence and survival after liver transplantation.

BACKGROUND: Preservation injury in the HCV liver transplant population has been reported to correlate with poorer survival outcomes compared to preservation injury in the non-HCV liver transplant population. However, determinants of progression to cirrhosis in HCV infection remain poorly defined in this population. AIM: This study aimed to determine if the presence and severity of preservation injury impact the acceleration of HCV recurrence and survival after liver transplant. METHODS: We retrospectively reviewed liver transplant HCV patients over a 10-year period. Biopsies from postoperative day 7 were assessed for preservation injury and 4- and 12-month biopsies were assessed for fibrosis. Patients with Ishak fibrosis >0.8 Units/year were considered rapid fibrosers. RESULTS: Our study group consisted of 255 patients. The mean age was 49.3 years old, 180 (70.6 %) were male, and 221 (86.7 %) were Caucasian. The incidence of preservation injury on the 7-day biopsy was 69.0 %. A strong correlation between postoperative peak AST within the first week and preservation injury was found. The overall prevalence of rapid fibrosers at 4 months, 1 and 2 years was 47.4, 75.2, and 58.9 %, respectively. The prevalence of rapid fibrosers at 4 months, 1 and 2 years between patients with or without preservation injury was not statistically significant (p = 0.39, p = 0.46, and p = 0.53, respectively). No differences were seen between patients with and without PI in terms of patient and graft survival. CONCLUSION: In this study, the presence and severity of preservation injury were not associated with development of rapid HCV recurrence or worsening in survival.

Best radiological response to trans-arterial chemoembolization for hepatocellular carcinoma does not imply better outcomes.

INTRODUCTION: Regional therapy with trans-arterial chemoembolization (TACE) is a common treatment for unresectable hepatocellular carcinoma (HCC). Outcomes were examined in patients with the best radiological response (BR) after the initial TACE. METHODS: This was a retrospective cohort study of patients who underwent TACE as the initial treatment for HCC between the years 2000 and 2010. BR was defined as complete disappearance of the tumour or no enhancement with contrast on the first cross-sectional imaging study after the initial TACE. RESULTS: Seventy-eight out of 104 total consecutive patients were identified with the potential for a BR to TACE therapy for unresectable HCC, and 24 met the criteria for BR. Patients with BR had a median survival of 12.8 months (2.2-54.9) compared with 18.9 months(1.3-56.7) for the entire cohort (P= 0.313). The median time to progression was 10.6 months (1.2-24.3) in the BR group and 3.2 months (0.7-49.2) in the patients without a BR (P= 0.003). DISCUSSION: BR to initial TACE for unresectable HCC is associated with comparable survival to those without BR in spite of a longer time to cancer progression. It may be reasonable to consider further therapy such as repeat TACE or biological/systemic therapy in patients with HCC even when the radiological response to the initial TACE is favourable.

Hepatic Resection and Transplant in Glycogen Storage Diseases.

Patients with glycogen storage diseases pose unique management challenges to clinicians.These challenges are exacerbated wheneverthey undergo surgery as the basic anomaly in their glycogen storage pathways make them susceptible to organic acidosis, which may in turn complicate their preoperative, intraoperative, and postoperative course. Because of the rarity of these diseases, clinicians may not be aware of the specific management concerns. In the case reported here, a 37-year-old patient with glycogen storage disease type 1 underwentleft hepatectomy for hepatic adenomatosis, which was complicated by intraoperative severe lactic acidosis that was successfully treated. After successful hepatectomy, the patient underwent liver transplant without major lactic acidosis or hemodynamic instability. Early recognition and aggressive management of blood sugar and lactic acidosis in patients with glycogen storage diseases can allow for successful outcomes even when complex surgical procedures are required.

Liver Transplant for Management of Hepatic Complications of Dyskeratosis Congenita: A Case Report.

Dyskeratosis congenita, a rare genetic disorder typified by progressive bone marrow failure, is classically characterized by the triad of abnormal skin pigmentation, nail dystrophy, and oral leukoplakia; however, it is a multisystem disease. Although hepatic involvement occurs in about 7% of patients with dyskeratosis congenita, end-stage liver disease is rare. Treatment of dyskeratosis congenita generally involves hematopoietic stem cell transplant. For patients with hepatic failure, liver transplant can be an option. Here, we describe a case of a patient with dyskeratosis congenita who presented with liver failure and pulmonary failure, precluding him from hematopoietic stem cell transplant. After liver transplant, the patient had significant improvements in pulmonary function and transfusion requirements, allowing the patient to qualify for hematopoietic stem cell transplant. Although hematopoietic stem cell transplant is typically the first step in the management of dyskeratosis congenita, for patients with severe hepatic manifestations of the disease, a liver transplant first approach may result in better disease management.

Nuclear receptor LXRß controls fitness and functionality of activated T cells.

T cells increase cholesterol biosynthesis upon activation to generate substrates for cellular growth and proliferation. The ubiquitously expressed liver X receptor ß (LXRß) encoded by the Nr1h2 gene is a critical regulator of cholesterol homeostasis in mammalian cells; however, its cell-intrinsic role in T cell biology remains poorly understood. We report that ablation of LXRß in T cells leads to spontaneous T cell activation and T lymphocytopenia. Unexpectedly, analysis of mixed bone marrow chimeric mice revealed a cell-autonomous survival defect that reduced the fitness of LXRß-deficient effector T cells, suggesting that the heightened immune activation in mice harboring LXRß-deficient T cells was due to impaired regulatory T (T reg) cell functionality. Indeed, we found that single-copy deletion of Nr1h2 in T reg cells disrupted activated T reg cell metabolism and fitness and resulted in early-onset fatal autoimmune disease. Our study demonstrated an indispensable requirement for T reg cell-intrinsic LXRß function in immune homeostasis and provides a basis for immunological therapies through targeting of this receptor.

Apprising the choice of bariatric surgery in patients with compensated cirrhosis with morbid obesity: results of a national analysis.

Bariatric surgery (BS) was proved safe in carefully selected patients with compensated cirrhosis (CC). However, limited data exist on differential impact of bariatric surgery type on clinical outcomes and health care utilization. This retrospective study utilizes the 2010-2014 Nationwide Readmissions Database. We included obese adults with CC who underwent the two most commonly used BS, Roux-en-Y (RYGB) and laparoscopic sleeve gastrectomy (LSG). Those with decompensation within 6 months of BS were excluded. Rates of hepatic decompensation (new-onset ascites, variceal bleed, encephalopathy, spontaneous bacterial peritonitis, and/or hepatorenal syndrome), surgical complications, health care utilization, and mortality were compared between RYGB and LSG. Multivariable analysis was performed to fit various models. A total of 3032 patients with CC underwent BS, including 1864 (61.5%) RYGB and 1168 (38.5%) LSG. The majority (56%) of BS were performed at large, metropolitan teaching hospitals. There were no significant differences in various decompensations and surgical complications comparing RYGB to LSG. Healthcare utilization including index length of stay (RYGB: 3.4 days vs LSG: 3.0 days), 30-day readmission rate (RYGB: 9.5% vs LSG: 3.7%), and cost of admission (RYGB: $14,006 vs LSG: $12,523) were higher in RYGB (p values < 0.001). Index admission and calendar year mortality could not be analyzed due to the few number of events. Two types of bariatric surgeries in obese patients with compensated cirrhosis have similar rates of decompensated cirrhosis events and surgical complications. However, RYGB procedure incurred increased healthcare utilization. Therefore, LSG may be the preferred BS for patients with CC. Prospective, randomized studies comparing the types of BS are needed to confirm our observations.

Temporal dynamics of persistent germinal centers and memory B cell differentiation following respiratory virus infection.

Following infection or immunization, memory B cells (MBCs) and long-lived plasma cells provide humoral immunity that can last for decades. Most principles of MBC biology have been determined with hapten-protein carrier models or fluorescent protein immunizations. Here, we examine the temporal dynamics of the germinal center (GC) B cell and MBC response following mouse influenza A virus infection. We find that antiviral B cell responses within the lung-draining mediastinal lymph node (mLN) and the spleen are distinct in regard to duration, enrichment for antigen-binding cells, and class switching dynamics. While splenic GCs dissolve after 6 weeks post-infection, mLN hemagglutinin-specific (HA+) GCs can persist for 22 weeks. Persistent GCs continuously differentiate MBCs, with "peak" and "late" GCs contributing equal numbers of HA+ MBCs to the long-lived compartment. Our findings highlight critical aspects of persistent GC responses and MBC differentiation following respiratory virus infection with direct implications for developing effective vaccination strategies.

Assembly of a spatial circuit of T-bet-expressing T and B lymphocytes is required for antiviral humoral immunity.

Effective antiviral immunity requires generation of T and B lymphocytes expressing the transcription factor T-bet, a regulator of type 1 inflammatory responses. Using T-bet expression as an endogenous marker for cells participating in a type 1 response, we report coordinated interactions of T-bet-expressing T and B lymphocytes on the basis of their dynamic colocalization at the T cell zone and B follicle boundary (T-B boundary) and germinal centers (GCs) during lung influenza infection. We demonstrate that the assembly of this circuit takes place in distinct anatomical niches within the draining lymph node, guided by CXCR3 that enables positioning of TH1 cells at the T-B boundary. The encounter of B and TH1 cells at the T-B boundary enables IFN-γ produced by the latter to induce IgG2c class switching. Within GCs, T-bet+ TFH cells represent a specialized stable sublineage required for GC growth but dispensable for IgG2c class switching. Our studies show that during respiratory viral infection, T-bet-expressing T and B lymphocytes form a circuit assembled in a spatiotemporally controlled manner that acts as a functional unit enabling a robust and coherent humoral response tailored for optimal antiviral immunity.