Increased Phagocyte FcγRI Expression and Improved Fcγ-Receptor–Mediated Phagocytosis After In Vivo Recombinant Human Interferon-γ Treatment of Normal Human Subjects

Cathepsin S Is More Abundant in Serum of Mycobacterium avium subsp. paratuberculosis-Infected Dairy Cows

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of bovine paratuberculosis, a chronic granulomatous enteritis leading to economic losses and posing a risk to human health due to its zoonotic potential. The pathogen cannot reliably be detected by standard methods, and immunological procedures during the infection are not well understood. Therefore, the aim of our study was to explore host-pathogen interactions in MAP-infected dairy cows and to improve diagnostic tests. Serum proteomics analysis using quantitative label-free LC-MS/MS revealed 60 differentially abundant proteins in MAP-infected dairy cows compared to healthy controls from the same infected herd and 90 differentially abundant proteins in comparison to another control group from an uninfected herd. Pathway enrichment analysis provided new insights into the immune response to MAP and susceptibility to the infection. Furthermore, we found a higher abundance of Cathepsin S (CTSS) in the serum of MAP-infected dairy cows, which is involved in multiple enriched pathways associated with the immune system. Confirmed with Western blotting, we identified CTSS as a potential biomarker for bovine paratuberculosis. This study enabled a better understanding of procedures in the host-pathogen response to MAP and improved detection of paratuberculosis-diseased cattle.

Antibody responses to Chlamydia trachomatis vaccine candidate antigens in Chlamydia-infected women and correlation with antibody-mediated phagocytosis of elementary bodies

Murine research has revealed a significant role for antibody responses in protection against Chlamydia reinfection. To explore potential humoral immune markers of protection elicited by Chlamydia trachomatis (CT) antigens in humans in the context of presumed clinical correlates of protection, we used both an IgG1-based ELISA and a conventional total IgG ELISA to evaluate antibody responses. We evaluated responses to five CT outer membrane proteins (PmpE, PmpF, PmpG, PmpH, and MOMP), along with other promising CT antigens (Pgp3 and HSP60), negative control antigens (RecO and AtpE), and CT elementary bodies (EBs) in sera from a well-characterized cohort of 60 women with different CT infection outcomes, including two outcomes that are likely clinical correlates of protective immunity: spontaneous resolution of infection and absence of reinfection after treatment. Furthermore, we used a flow cytometry-based assay to measure antibody-mediated phagocytosis by neutrophils in these sera. Results demonstrated that IgG1 ELISA displayed higher sensitivity than conventional total IgG ELISA in assessing antibody responses to CT EBs and antigens. Pgp3 IgG1 ELISA exhibited the highest sensitivity compared to IgG1 ELISA incorporating CT EBs or other antigens, confirming Pgp3 IgG1 ELISA as an ideal assay for CT antibody detection. Most (95%) sera from women with CT infection outcomes exhibited antibody-mediated phagocytosis of CT EBs, which was significantly correlated with IgG1 antibody responses to MOMP, Pgp3, HSP60, and PmpF. However, neither IgG1 responses to CT antigens and EBs nor antibody-mediated phagocytosis were associated with clinical correlates of protection. These findings suggest that neither CT IgG1 antibody detection nor antibody-mediated phagocytosis will be useful as immune correlates of protection against CT infection in humans.

Diagnostic and Prognostic Value of Peripheral Neutrophil CD64 Index in Elderly Patients with Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) is a leading cause of hospitalization and mortality in the elderly. The peripheral blood neutrophil CD64 (nCD64) index is increasingly recognized for its association with poor pneumonia prognosis. A comprehensive investigation involving 128 elderly patients diagnosed with CAP, including 96 with non-severe CAP and 32 with severe CAP, from January 2020 to January 2021 was performed. The nCD64 index, CD4+, CD8+, C-reactive protein (CRP), white blood cell (WBC) count, procalcitonin (PCT), neutrophil (NEUT), and B lymphocyte count were determined using flow cytometry. Our findings reveal that patients with severe CAP exhibited significantly higher levels of nCD64 index, NEUT, WBC, CRP, and PCT. Intriguingly, lower CRP, nCD64 index, CURB-65 score, and PCT were associated with a higher survival rate. Notably, the nCD64 index demonstrated remarkable predictive efficiency for 28-d survival in CAP patients [area under the curve (AUC) = 0.907], surpassing other markers and even showing enhanced predictive power when combined with the CURB-65 score (AUC = 0.905). Furthermore, a negative association was observed between the nCD64 index and both CD4+, CD4+/CD8+ ratios, and B lymphocytes, highlighting its potential role in immune dysregulation. These findings underscore the critical importance of the nCD64 index in the early diagnosis, risk stratification, and prognostic evaluation of infections and immune responses in elderly CAP patients.

Human neutrophil Fc gamma receptors: different buttons for different responses

Neutrophils are fundamental cells in host defense. These leukocytes are quickly recruited from the blood to sites of infection or tissue damage. At these sites, neutrophils initiate several innate immune responses, including phagocytosis, production of reactive oxygen species, degranulation to release proteases and other antimicrobial compounds, production of inflammatory mediators, and formation of neutrophil extracellular traps. In addition to their role in innate immunity, neutrophils are now recognized as cells that also regulate adaptive immunity, via interaction with dendritic cells and lymphocytes. Neutrophils also respond to adaptive immunity by interacting with antibody molecules. Indeed, antibody molecules allow neutrophils to have antigen-specific responses. Neutrophils express different receptors for antibodies. The receptors for immunoglobulin G molecules are known as Fcγ receptors. Upon Fcγ receptor aggregation on the cell membrane, these receptors trigger distinct signal transduction cascades that activate particular cellular responses. In this review, we describe the major Fcγ receptors expressed on human neutrophils and discuss how each Fcγ receptor activates a choice of signaling pathways to stimulate particular neutrophil responses.

Role of histamine-mediated macrophage differentiation in clearance of metastatic bacterial infection

Macrophages are highly heterogeneous immune cells with a role in maintaining tissue homeostasis, especially in activating the defense response to bacterial infection. Using flow cytometric and single-cell RNA-sequencing analyses of peritoneal cells, we here show that small peritoneal macrophage and immature macrophage populations are enriched in histamine-deficient (Hdc -/-) mice, characterized by a CD11bmiF4/80loCCR2+MHCIIhi and CD11bloF4/80miTHBS1+IL-1α+ phenotype, respectively. Molecular characterization revealed that immature macrophages represent an abnormally differentiated form of large peritoneal macrophages with strong inflammatory properties. Furthermore, deficiency in histamine signaling resulted in significant impairment of the phagocytic activity of peritoneal macrophage populations, conferring high susceptibility to bacterial infection. Collectively, this study reveals the importance of histamine signaling in macrophage differentiation at the molecular level to maintain tissue homeostasis, offering a potential therapeutic target for bacterial infection-mediated diseases.

Serum CD64 as a Marker for Chronic Periprosthetic Joint Infection

Background

Serum cluster of differentiation 64 (CD64) has emerged as a diagnostic test for musculoskeletal infections. The purpose of this study was to evaluate the utility of serum CD64 in diagnosing periprosthetic joint infections (PJIs) compared to conventional markers like white blood count (WBC), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and interleukin-6 (IL-6).

Methods

A prospective case-control study on patients undergoing revision hip or knee arthroplasty surgery >6 weeks after their index surgery was performed at a single institution. Whole blood samples were drawn within 24 hours prior to revision surgery for white blood count, ESR, CRP, IL-6, and CD64. Intraoperative cultures were obtained during the revision, and PJI was defined using the major criteria from the 2018 Musculoskeletal Infection Society criteria. Two-sample Wilcoxon rank-sum test and Fisher's exact test were used to determine if there were significant differences in serum laboratory values between patients with and without infection. The sensitivity, specificity, positive predictive value (PPV), negative predictive value, and accuracy of each test were calculated.

Results

With an average age of 67 years, 39 patients with 15 revision THAs and 24 TKAs, were included. 19 patients (48.7%) were determined to have PJI. Patients with PJI had significantly higher CD64 (P = .036), CRP (P = .016), and ESR (P = .045). CD64 had the highest specificity (100%) and PPV (100%), moderate accuracy (69.2%), but low sensitivity (37.0%) and negative predictive value (62.5%).

Conclusions

Given the high specificity, PPV, and accuracy, CD64 may be an excellent confirmatory test to help diagnose PJI.

Point-of-care neutrophil CD64 as a rule in diagnostic test for bacterial infections in the emergency department

INTRODUCTION

Bacterial infections are frequently seen in the emergency department (ED), but can be difficult to distinguish from viral infections and some non-infectious diseases. Common biomarkers such as c-reactive protein (CRP) and white blood cell (WBC) counts fail to aid in the differential diagnosis. Neutrophil CD64 (nCD64), an IgG receptor, is suggested to be more specific for bacterial infections. This study investigated if nCD64 can distinguish bacterial infections from other infectious and non-infectious diseases in the ED.

METHODS

All COVID-19 suspected patients who visited the ED and for which a definitive diagnosis was made, were included. Blood was analyzed using an automated flow cytometer within 2 h after presentation. Patients were divided into a bacterial, viral, and non-infectious disease group. We determined the diagnostic value of nCD64 and compared this to those of CRP and WBC counts.

RESULTS

Of the 291 patients presented at the ED, 182 patients were included with a definitive diagnosis (bacterial infection n = 78; viral infection n = 64; non-infectious disease n = 40). ROC-curves were plotted, with AUCs of 0.71 [95%CI: 0.64-0.79], 0.77 [0.69-0.84] and 0.64 [0.55-0.73] for nCD64, WBC counts and CRP, respectively. In the bacterial group, nCD64 MFI was significantly higher compared to the other groups (p < 0.01). A cut-off of 9.4 AU MFI for nCD64 corresponded with a positive predictive value of 1.00 (sensitivity of 0.27, a specificity of 1.00, and an NPV of 0.64). Furthermore, a diagnostic algorithm was constructed which can serve as an example of what a future biomarker prediction model could look like.

CONCLUSION

For patients in the ED presenting with a suspected infection, nCD64 measured with automatic flow cytometry, has a high specificity and positive predictive value for diagnosing a bacterial infection. However, a low nCD64 cannot rule out a bacterial infection. For future purposes, nCD64 should be combined with additional tests to form an algorithm that adequately diagnoses infectious diseases.

Microbiota-dependent and -independent postnatal development of salivary immunity

While saliva regulates the interplay between the microbiota and the oral immune system, the mechanisms establishing postnatal salivary immunity are ill-defined. Here, we show that high levels of neutrophils and neonatal Fc receptor (FcRn)-transferred maternal IgG are temporarily present in the neonatal murine salivary glands in a microbiota-independent manner. During weaning, neutrophils, FcRn, and IgG decrease in the salivary glands, while the polymeric immunoglobulin receptor (pIgR) is upregulated in a growth arrest-specific 6 (GAS6)-dependent manner independent of the microbiota. Production of salivary IgA begins following weaning and relies on CD4-help, IL-17, and the microbiota. The weaning phase is characterized by a transient accumulation of dendritic cells capable of migrating from the oral mucosa to the salivary glands upon exposure to microbial challenges and activating T cells. This study reveals the postnatal mechanisms developed in the salivary glands to induce immunity and proposes the salivary glands as an immune inductive site.

FcγRI FG-loop functions as a pH sensitive switch for IgG binding and release

Understanding the molecular mechanism underlying the hierarchic binding between FcγRs and IgG antibodies is critical for therapeutic antibody engineering and FcγR functions. The recent determination of crystal structures of FcγRI-Fc complexes, however, resulted in two controversial mechanisms for the high affinity receptor binding to IgG. Here, we describe high resolution structures of a bovine FG-loop variant of FcγRI in complex with the Fc fragment of IgG₁ crystallized in three different conditions at neutral pH, confirming the characteristic FG loop-Fc interaction is critical to the high affinity immunoglobulin binding. We showed that the FcγRI D2-domain FG-loop functioned as a pH-sensing switch for IgG binding. Further live cell imaging of FcγRI-mediated internalization of immune complexes showed a pH sensitive temporal-spatial antibody-antigen uptake and release. Taken together, we demonstrate that the structures of FcγRI-Fc crystallized at neutral and acidic pH, respectively, represent the high and low affinity binding states of the receptor for IgG uptake and release. These results support a role for FcγRI in antigen delivery, highlight the importance of Fc glycan in antibody binding to the high affinity receptor and provide new insights to future antibody engineering.

Longitudinal assessment of the inflammatory response: The next step in personalized medicine after severe trauma

Infections in trauma patients are an increasing and substantial cause of morbidity, contributing to a mortality rate of 5-8% after trauma. With increased early survival rates, up to 30-50% of multitrauma patients develop an infectious complication. Trauma leads to a complex inflammatory cascade, in which neutrophils play a key role. Understanding the functions and characteristics of these cells is important for the understanding of their involvement in the development of infectious complications. Recently, analysis of neutrophil phenotype and function as complex biomarkers, has become accessible for point-of-care decision making after trauma. There is an intriguing relation between the neutrophil functional phenotype on admission, and the clinical course (e.g., infectious complications) of trauma patients. Potential neutrophil based cellular diagnostics include subsets based on neutrophil receptor expression, responsiveness of neutrophils to formyl-peptides and FcγRI (CD64) expression representing the infectious state of a patient. It is now possible to recognize patients at risk for infectious complications when presented at the trauma bay. These patients display increased numbers of neutrophil subsets, decreased responsiveness to fMLF and/or increased CD64 expression. The next step is to measure these biomarkers over time in trauma patients at risk for infectious complications, to guide decision making regarding timing and extent of surgery and administration of (preventive) antibiotics.

Leveraging Antibody, B Cell and Fc Receptor Interactions to Understand Heterogeneous Immune Responses in Tuberculosis

Despite over a century of research, Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), continues to kill 1.5 million people annually. Though less than 10% of infected individuals develop active disease, the specific host immune responses that lead to Mtb transmission and death, as well as those that are protective, are not yet fully defined. Recent immune correlative studies demonstrate that the spectrum of infection and disease is more heterogenous than has been classically defined. Moreover, emerging translational and animal model data attribute a diverse immune repertoire to TB outcomes. Thus, protective and detrimental immune responses to Mtb likely encompass a framework that is broader than T helper type 1 (Th1) immunity. Antibodies, Fc receptor interactions and B cells are underexplored host responses to Mtb. Poised at the interface of initial bacterial host interactions and in granulomatous lesions, antibodies and Fc receptors expressed on macrophages, neutrophils, dendritic cells, natural killer cells, T and B cells have the potential to influence local and systemic adaptive immune responses. Broadening the paradigm of protective immunity will offer new paths to improve diagnostics and vaccines to reduce the morbidity and mortality of TB.

Utility of monocyte parameters in diagnosing Sputum Smear Negative Pulmonary TB

Background - Smear-negative TB (SNTB) may remain undetected for a long duration and new bio-markers are needed for diagnosis. Our study investigated monocyte parameters in this regard.

Thirty cases each of SNTB, sputum positive cases and healthy controls were included. Full blood count and immune-phenotyping for ‘monocyte parameters’ by flow cytometry were performed using CD45, CD16, CD14, CD64 and HLA-DR The percentage of monocyte subsets and MFI of CD64 and HLA- DR noted and data statistically compared.

The monocyte to lymphocyte ratio, percentage of intermediate monocytes, expression of CD64 on total as well as intermediate monocytes were significantly elevated in cases with SNTB as compared to healthy controls (p value, 0.07, 0.07, 0.001, 0.001 respectively). The cut off value for MFI CD64 on total and intermediate monocyte was >18 and >19.6 respectively.

Thus monocyte parameters can serve as useful biomarkers for diagnosing tuberculosis in the sputum negative group.

Antimicrobial Activity of Neutrophils Against Mycobacteria

The mycobacterium genus contains a broad range of species, including the human pathogens M. tuberculosis and M. leprae. These bacteria are best known for their residence inside host cells. Neutrophils are frequently observed at sites of mycobacterial infection, but their role in clearance is not well understood. In this review, we discuss how neutrophils attempt to control mycobacterial infections, either through the ingestion of bacteria into intracellular phagosomes, or the release of neutrophil extracellular traps (NETs). Despite their powerful antimicrobial activity, including the production of reactive oxidants such as hypochlorous acid, neutrophils appear ineffective in killing pathogenic mycobacteria. We explore mycobacterial resistance mechanisms, and how thwarting neutrophil action exacerbates disease pathology. A better understanding of how mycobacteria protect themselves from neutrophils will aid the development of novel strategies that facilitate bacterial clearance and limit host tissue damage.

Blood neutrophils from children with COVID-19 exhibit both inflammatory and anti-inflammatory markers

Background

Perhaps reflecting that children with COVID-19 rarely exhibit severe respiratory symptoms and often remain asymptomatic, little attention has been paid to explore the immune response in pediatric COVID-19. Here, we analyzed the phenotype and function of circulating neutrophils from children with COVID-19.

Methods

An observational study including 182 children with COVID-19, 21 children with multisystem inflammatory syndrome (MIS-C), and 40 healthy children was performed in Buenos Aires, Argentina. Neutrophil phenotype was analyzed by flow cytometry in blood samples. Cytokine production, plasma levels of IgG antibodies directed to the spike protein of SARS-CoV-2 and citrullinated histone H3 were measured by ELISA. Cell-free DNA was quantified by fluorometry.

Findings

Compared with healthy controls, neutrophils from children with COVID-19 showed a lower expression of CD11b, CD66b, and L-selectin but a higher expression of the activation markers HLA-DR, CD64 and PECAM-1 and the inhibitory receptors LAIR-1 and PD-L1. No differences in the production of cytokines and NETs were observed. Interestingly, the expression of CD64 in neutrophils and the serum concentration of IgG antibodies directed to the spike protein of SARS-CoV-2 distinguished asymptomatic from mild and moderate COVID-19.

Interpretation

Acute lung injury is a prominent feature of severe COVID-19 in adults. A low expression of adhesion molecules together with a high expression of inhibitory receptors in neutrophils from children with COVID-19 might prevent tissue infiltration by neutrophils preserving lung function.

Differential expression of CD64 in patients with Mycobacterium tuberculosis infection: A potential biomarker for clinical diagnosis and prognosis

To evaluate the clinical utility of neutrophil (n)CD64 index to diagnose pulmonary tuberculosis (PTB) and extrapulmonary TB (ePTB) and to predict the outcome of Mycobacterium tuberculosis infection. We recruited 189 patients with active TB and 140 controls and measured the differential expression of nCD64 index using flow cytometry. The receiver operating characteristics (ROC) curve analysis was performed to estimate the diagnostic performance of the nCD64 index and T‐SPOT.TB assay for the diagnosis of TB. Furthermore, we analysed whether the nCD64 index in patients with TB was correlated with inflammatory indicators. Finally, we assessed the prognosis of patients by following the dynamic changes of the nCD64 index once a week. The nCD64 index was significantly higher in active TB group (PTB and ePTB), than in the anti‐TB and healthy controls (HC) groups. The sensitivity and specificity of nCD64 index for the differential diagnosis of PTB and pneumonia (PN) patients were 68.33% and 77.55%, respectively. The sensitivity and specificity of nCD64 index for the diagnosis of tuberculous meningitis (TBM) were 53.85% and 100%, respectively. Furthermore, there was a weak correlation between the nCD64 index and inflammatory indicators. More importantly, with the improvement in patient condition, the nCD64 index started to decline in the first week of anti‐TB therapy and significantly decreased at 4 weeks after treatment. Our study demonstrated that the CD64 assay is a rapid, non‐invasive and stable method for clinical application, and the nCD64 index can serve as a potential biomarker for the diagnosis and prognosis of TB.

Evaluation of synovial fluid neutrophil CD64 index as a screening biomarker of prosthetic joint infection

AIMS

Prosthetic joint infection (PJI) remains a major clinical challenge. Neutrophil CD64 index, Fc-gamma receptor 1 (FcγR1), plays an important role in mediating inflammation of bacterial infections and therefore could be a valuable biomarker for PJI. The aim of this study is to compare the neutrophil CD64 index in synovial and blood diagnostic ability with the standard clinical tests for discrimination PJI and aseptic implant failure.

METHODS

A total of 50 patients undergoing revision hip and knee arthroplasty were enrolled into a prospective study. According to Musculoskeletal Infection Society (MSIS) criteria, 25 patients were classified as infected and 25 as not infected. In all patients, neutrophil CD64 index and percentage of polymorphonuclear neutrophils (PMN%) in synovial fluid, serum CRP, ESR, and serum CD64 index levels were measured preoperatively. Receiver operating characteristic (ROC) curves and the area under the curve (AUC) were analyzed for each biomarker.

RESULTS

Serum CD64 index showed no significant difference between the two groups (p = 0.091). Synovial fluid CD64 index and PMN% discriminated good differentiation between groups of PJI and aseptic failure with AUC of 0.946 (95% confidence interval (CI) 0.842 to 0.990) and 0.938 (95% CI 0.832 to 0.987) separately. The optimal threshold value of synovial CD64 index for the diagnosis of PJI was 0.85, with a sensitivity of 92.00%, a specificity of 96.00%, and diagnostic odds ratio (DOR) of 227.11.

CONCLUSION

The present study demonstrates that CD64 index in synovial fluid could be a promising laboratory marker for screening PJI. The cut-off values of 0.85 for synovial CD64 index has the potential to distinguish aseptic failure from PJI. Cite this article: Bone Joint J 2020;102-B(4):463-469.

Expression, Role, and Regulation of Neutrophil Fcγ Receptors

Neutrophils are best known for their critical role in host defense, for which they utilize multiple innate immune mechanisms, including microbe-associated pattern recognition, phagocytosis, production of reactive oxygen species, and the release of potent proteases, mediators, antimicrobials, and neutrophil extracellular traps. Beyond their well-established contribution to innate immunity, neutrophils were more recently reported to interact with various other cell types, including cells from the adaptive immune system, thereby enabling neutrophils to tune the overall immune response of the host. Neutrophils express different receptors for IgG antibodies (Fcγ receptors), which facilitate the engulfment of IgG-opsonized microbes and trigger cell activation upon cross-linking of several receptors. Indeed, FcγRs (via IgG antibodies) confer neutrophils with a key feature of the adaptive immunity: an antigen-specific cell response. This review summarizes the expression and function of FcγRs on human neutrophils in health and disease and how they are affected by polymorphisms in the FCGR loci. Additionally, we will discuss the role of neutrophils in providing help to marginal zone B cells for the production of antibodies, which in turn may trigger neutrophil effector functions when engaging FcγRs.

Can biomarkers improve the rational use of antibiotics?

PURPOSE OF REVIEW

We aim to review recent literature about the use of biomarkers to guide the initiation and duration of antibiotic treatments for suspected bacterial infections.

RECENT FINDINGS

Several good quality meta-analyses show that procalcitonin can be safely used to guide antibiotic-related decisions, especially for respiratory infections, thereby decreasing unnecessary antibiotic exposure. Furthermore, the use of CRP-based algorithms to guide antibiotic initiation in primary care patients with acute respiratory infections is associated with a reduction in antibiotic use without an increase in adverse events. Regarding neutrophil CD64 and serum amyloid A, more good-quality evidence is needed to assess their utility as biomarkers to tailor antibiotic use. Finally, transcriptomics, metabolomics and proteomics are promising tools for the development of tests to differentiate specific host responses to viral, bacterial and noninfectious stimuli, but such tests still need further validation.

SUMMARY

Evidence shows that the use of biomarkers, procalcitonin and CRP, can safely reduce unnecessary antibiotic prescriptions in certain infectious syndromes. The clinical utility of host-based strategies such as transcriptomics, metabolomics and proteomics for the diagnosis of infectious diseases has yet to be evaluated, as well as considerations such as costs, technical complexity and result turnaround time.

Update on Neutrophil Function in Severe Inflammation

Neutrophils are main players in the effector phase of the host defense against micro-organisms and have a major role in the innate immune response. Neutrophils show phenotypic heterogeneity and functional flexibility, which highlight their importance in regulation of immune function. However, neutrophils can play a dual role and besides their antimicrobial function, deregulation of neutrophils and their hyperactivity can lead to tissue damage in severe inflammation or trauma. Neutrophils also have an important role in the modulation of the immune system in response to severe injury and trauma. In this review we will provide an overview of the current understanding of neutrophil subpopulations and their function during and post-infection and discuss the possible mechanisms of immune modulation by neutrophils in severe inflammation.

Time Course of CD64, a Leukocyte Activation Marker, During Cardiopulmonary Bypass Surgery

Distinction between inflammation secondary to surgery, especially coronary artery bypass graft with cardiopulmonary bypass (CPB), and inflammation due to infection is difficult in surgical intensive care unit (ICU) patients. Development of biomarkers of infection could help clinicians in the early identification and thus treatment of sepsis in these patients. We compared the time course of the neutrophil CD64 index, a high affinity immunoglobulin FC γ receptor I whose expression is increased in bacterial infection, in 39 patients undergoing cardiac surgery with CPB and 11 patients admitted to the ICU with severe sepsis or septic shock. The CD64 index was significantly more elevated in septic patients than in patients who had CPB except at day 5. The CD64 index increased moderately on day 1 after cardiac surgery but the value remained lower than in septic patients. The duration for which the CD64 index was greater than 1.0 was longer in septic than in CPB patients. Receiver operating curves to differentiate CPB from sepsis on day 1 were not significantly different between C-reactive protein (CRP) concentrations and CD 64 index. Nevertheless, combination of low CD64 index with low CRP concentrations on day 1 ruled out sepsis except in three patients. There were no correlations between the CD64 index and cytokine levels (tumor necrosis factor [TNF]-α, interferon [IFN]γ, interleukin [IL]-6, IL-10, IL-8, IL-12) measured in subpopulations. In conclusion, CD64 index only in combination with CRP concentrations could be used to discriminate inflammation due to surgery from that due to infection in this particular population.

Correlation of Neutrophil CD64 with Clinical Profile and Outcome of Sepsis Patients during Intensive Care Unit Stay

Introduction:

Neutrophil CD64 (nCD64) has been found to identify sepsis from nonseptic patients. It is also reported to be a predictor of survival and severity of sepsis. The goal of this study was to correlate serial nCD64 with Intensive Care Unit (ICU) outcome and severity of sepsis.

Materials and Methods:

A prospective observational study was conducted in 12-bedded critical care unit of a tertiary care center. Adult patients with sepsis were included in this study. Demographics, illness severity scores, clinical parameters, laboratory data, and 28-day outcome were recorded. Serial nCD64 analysis was done (on days 0, 4, and 8) in consecutive patients.

Results:

Fifty-one consecutive patients were included in the study. Median Acute Physiology and Chronic Health Evaluation II was 16 (12–20) and mean Sequential Organ Failure Assessment was 9 (8–10). Compared to survivors, nonsurvivors had higher nCD64 on day 8 (P = 0.001). nCD64 was higher in the septic shock group compared to sepsis group on days 0 and 8 (P < 0.05). Survivors showed improving trend of nCD64 over time while nonsurvivors did not. This trend was similar in the presence or absence of septic shock. nCD64 count was a good predictor of the septic shock on day 0 (area under the curve [AUC] = 0.747, P = 0.010) and moderate predictor at day 8 (AUC = 0.679, P = 0.028).

Conclusion:

Monitoring serial nCD64 during ICU stay may be helpful in determining the clinical course of septic patients.

Novel biomarkers for sepsis: A narrative review

BACKGROUND

Sepsis is a prevalent condition among hospitalized patients that carries a high risk of morbidity and mortality. Rapid recognition of sepsis as the cause of deterioration is desirable, so effective treatment can be initiated rapidly. Traditionally, diagnosis was based on presence of two or more positive SIRS criteria due to infection. However, recently published sepsis-3 criteria put more emphasis on organ dysfunction caused by infection in the definition of sepsis. Regardless of this, no gold standard for diagnosis exist, and clinicians still rely on a number of traditional and novel biomarkers to discriminate between patients with and without infection, as the cause of deterioration.

METHOD

Narrative review of current literature.

RESULTS

A number of the most promising biomarkers for diagnoses and prognostication of sepsis are presented.

CONCLUSION

Procalcitonin, presepsin, CD64, suPAR, and sTREM-1 are the best evaluated biomarkers for diagnosis and prognostication of sepsis to date. All have limitations in differentiation between infected and non-infected patients with SIRS, and their future role in diagnosis needs to be evaluated. It is important to test utility, performance, and validity of future biomarkers before implementing them in routine clinical care.

Neutrophils Are Central to Antibody-Mediated Protection against Genital Chlamydia

Determining the effector populations involved in humoral protection against genital chlamydia infection is crucial to development of an effective chlamydial vaccine. Antibody has been implicated in protection studies in multiple animal models, and we previously showed that the passive transfer of immune serum alone does not confer immunity in the mouse. Using the Chlamydia muridarum model of genital infection, we demonstrate a protective role for both Chlamydia-specific immunoglobulin G (IgG) and polymorphonuclear neutrophils and show the importance of an antibody/effector cell interaction in mediating humoral immunity. While neutrophils were found to contribute significantly to antibody-mediated protection in vivo, natural killer (NK) cells were dispensable for protective immunity. Furthermore, gamma interferon (IFN-γ)-stimulated primary peritoneal neutrophils (PPNs) killed chlamydiae in vitro in an antibody-dependent manner. The results from this study support the view that an IFN-γ-activated effector cell population cooperates with antibody to protect against genital chlamydia and establish neutrophils as a key effector cell in this response.

Human CD64-targeted non-viral siRNA delivery system for blood monocyte gene modulation

A subset of phagocytes including inflammatory monocytes in blood migrate and give rise to macrophages in inflammatory tissues which generated the idea that blood monocytes are the therapeutic targets for drug delivery. Fc gamma receptor I (CD64) is a membrane receptor for the Fc region of immunoglobulin G, primarily expressed on monocyte-lineage, and H22 a monoclonal antibody for human CD64 had shown rapid blood monocyte binding and occupation in clinical studies. Small interfering RNA-mediated gene silencing as a therapeutic has been proposed and is a promising strategy in terms of its "knock-down" ability on the target gene prior to translation. However, its instability and off-targeting effect must be overcome for success in clinical studies. In this study, we developed a non-viral delivery system composed of oligo-nona-arginine (9R) and anti-human CD64 single chain antibodies (H22) for human monocyte-specific siRNA delivery. A targeted and efficient siRNA delivery mediated by anti-CD64 scFv-9R was observed in CD64 positive human leukemia cells, THP-1. With primary human blood cells, anti-CD64 scFv-9R mediated gene silencing was quantitatively confirmed representing blood monocyte selective gene delivery. These results demonstrate the potential of anti-CD64 scFv-9R mediated siRNA delivery for the treatment of human inflammatory diseases via blood monocytes gene delivery.

The Expression Level of Neutrophil CD64 Is a Useful Marker of Systemic Inflammation Associated with HIV Infection

CD64 is an Fc-gamma-receptor type 1. The expression level of neutrophil CD64 (nCD64) is a known bacterial infection marker, and it also increases in viral infections. We examined the absolute nCD64 before and after the initiation of antiretroviral therapy (ART) to determine its role as an infection and inflammation marker of human immunodeficiency virus (HIV) infection. In this prospective observational study, 94 HIV-infected patients were enrolled and classified into ART (n = 62), ART naive (n = 24), and acute/early phase groups (n = 8). The median nCD64 was 1,430 molecules/cell in the ART group, 2,994 in the ART naive group, 4,625 in the acute/early phase group, and 1,196 in the healthy control group. The nCD64 in the ART group was significantly higher compared with the healthy controls (p = .041), and the nCD64 in the ART naive and acute/early phase groups was significantly higher compared with the ART group (both p < .001). In the ART naive group, nCD64 was significantly higher in patients with than without concomitant infections (3,942 ± 1,519 vs. 2,300 ± 784, p = .004). However, this was influenced by the fact that nCD64 elevated as the stage of HIV infection progressed. nCD64 decreased significantly during the 24 weeks after starting ART (p = .004), although an upward trend in nCD64 was observed at weeks 2 and 4, without symptoms. When immune reconstitution inflammatory syndrome occurred, nCD64 elevated with a wider range than did C-reactive protein. This preliminary study suggests that nCD64 would be useful as a marker of the systemic inflammation of HIV-infected patients.

IFNγ is Required for Optimal Antibody-Mediated Immunity against Genital Chlamydia Infection

Defining the mechanisms of immunity conferred by the combination of antibody and CD4⁺ T cells is fundamental to designing an efficacious chlamydial vaccine. Using the Chlamydia muridarum genital infection model of mice, which replicates many features of human C. trachomatis infection and avoids the characteristic low virulence of C. trachomatis in the mouse, we previously demonstrated a significant role for antibody in immunity to chlamydial infection. We found that antibody alone was not protective. Instead, protection appeared to be conferred through an undefined antibody-cell interaction. Using gene knockout mice and in vivo cellular depletion methods, our data suggest that antibody-mediated protection is dependent on the activation of an effector cell population in genital tract tissues by CD4⁺ T cells. Furthermore, the CD4⁺ T cell-secreted cytokine gamma interferon (IFN-γ) was found to be a key component of the protective antibody response. The protective function of IFN-γ was not related to the immunoglobulin class or to the magnitude of the Chlamydia-specific antibody response or to recruitment of an effector cell population to genital tract tissue. Rather, IFN-γ appears to be necessary for activation of the effector cell population that functions in antibody-mediated chlamydial immunity. Our results confirm the central role of antibody in immunity to chlamydia reinfection and demonstrate a key function for IFN-γ in antibody-mediated protection.

The many faces of FcγRI: implications for therapeutic antibody function

Fcγ receptor I (FcγRI or CD64) is the sole human Fc receptor with high affinity for monovalent IgG. While it contains an immunoreceptor tyrosine-based activation motif in its cytoplasmic domain, binding of FcγRI can result in a complex array of activating and inhibitory outcomes. For instance, binding of monomeric IgG provides a low-intensity tonic signal through FcγRI that is necessary for full interferon γ receptor signaling in the same cell. Interaction of FcγRI with larger high-avidity complexes can result in phagocytosis, the generation of reactive oxygen species, as well as the synthesis and release of inflammatory cytokines. However, numerous reports also document potent anti-inflammatory effects brought about by FcγRI engagement with immune complexes such as the inhibition of IFNγ and TLR4 signaling, and secretion of interleukin-10. This has led to conflicting hypotheses regarding the function of FcγRI, especially with regard to its role in the efficacy of several therapeutic monoclonal antibodies. While many of these issues are still unclear, continued characterization of the regulation and context dependence of FcγRI function, as well as the molecular mechanisms responsible for these various outcomes, will improve our understanding of FcγRI biology as well as the therapeutic strategies designed to harness or constrain its actions.

CD64 and Group II Secretory Phospholipase A2 (sPLA2-IIA) as Biomarkers for Distinguishing Adult Sepsis and Bacterial Infections in the Emergency Department

INTRODUCTION

Early diagnosis of sepsis and bacterial infection is imperative as treatment relies on early antibiotic administration. There is a need to develop new biomarkers to detect patients with sepsis and bacterial infection as early as possible, thereby enabling prompt antibiotic treatment and improving the survival rate.

METHODS

Fifty-one adult patients with suspected bacterial sepsis on admission to the Emergency Department (ED) of a teaching hospital were included into the study. All relevant cultures and serology tests were performed. Serum levels for Group II Secretory Phospholipase A2 (sPLA2-IIA) and CD64 were subsequently analyzed.

RESULTS AND DISCUSSION

Sepsis was confirmed in 42 patients from a total of 51 recruited subjects. Twenty-one patients had culture-confirmed bacterial infections. Both biomarkers were shown to be good in distinguishing sepsis from non-sepsis groups. CD64 and sPLA2-IIA also demonstrated a strong correlation with early sepsis diagnosis in adults. The area under the curve (AUC) of both Receiver Operating Characteristic curves showed that sPLA2-IIA was better than CD64 (AUC = 0.93, 95% confidence interval (CI) = 0.83-0.97 and AUC = 0.88, 95% CI = 0.82-0.99, respectively). The optimum cutoff value was 2.13μg/l for sPLA2-IIA (sensitivity = 91%, specificity = 78%) and 45 antigen bound cell (abc) for CD64 (sensitivity = 81%, specificity = 89%). In diagnosing bacterial infections, sPLA2-IIA showed superiority over CD64 (AUC = 0.97, 95% CI = 0.85-0.96, and AUC = 0.95, 95% CI = 0.93-1.00, respectively). The optimum cutoff value for bacterial infection was 5.63μg/l for sPLA2-IIA (sensitivity = 94%, specificity = 94%) and 46abc for CD64 (sensitivity = 94%, specificity = 83%).

CONCLUSIONS

sPLA2-IIA showed superior performance in sepsis and bacterial infection diagnosis compared to CD64. sPLA2-IIA appears to be an excellent biomarker for sepsis screening and for diagnosing bacterial infections, whereas CD64 could be used for screening bacterial infections. Both biomarkers either alone or in combination with other markers may assist in decision making for early antimicrobial administration. We recommend incorporating sPLA2-IIA and CD64 into the diagnostic algorithm of sepsis in ED.

FcγR requirements leading to successful immunotherapy

Monoclonal antibody (mAb) immunotherapy is currently experiencing an unprecedented amount of success, delivering blockbuster sales for the pharmaceutical industry. Having experienced several false dawns and overcoming technical issues which limited progress, we are now entering a golden period where mAbs are becoming a mainstay of treatment regimes for diseases ranging from cancer to autoimmunity. In this review, we discuss how these mAbs are most likely working and focus in particular on the key receptors that they interact with to precipitate their therapeutic effects. Although their targets may vary, their engagement with Fcγ receptors (FcγRs) on numerous immune effector cells is almost universal, and here we review their roles in delivering successful immunotherapy.

Elevated Membrane and Soluble CD64: A Novel Marker Reflecting Altered FcγR Function and Disease in Early Rheumatoid Arthritis That Can Be Regulated by Anti-Rheumatic Treatment

OBJECTIVES

Fc receptors (FcR) interacting with immune complexes (ICs) is a central event in the immune pathogenesis of rheumatoid arthritis (RA). Here we asked if a specific FcR is linked to RA pathogenesis and if FcR activities relate to disease and treatment outcome in early RA.

MATERIAL AND METHODS

Twenty autoantibody-positive RA patients and 33 HC were included. The patients were evaluated before and after treatment with methotrexate and prednisolone. At follow-up, the EULAR response criteria were applied to determine the individual treatment outcomes. Serum immunoglobulin levels were measured and the expression of FcR for IgG (FcγR) and IgA (FcαR) on peripheral blood monocytes were determined by flow cytometry. The monocytic FcγR function was evaluated by human IgG1 and IgG3 IC-binding and TNFα stimulated release. Plasma levels of soluble FcRs (sFcRs) were determined with ELISA.

RESULTS

The IgG1 and IgG3 levels were elevated in the RA sera. The RA monocytes expressed more CD64 and cell surface-bound IgG than HC monocytes, and showed an impaired FcγR function as reflected by changes in IC-binding and decreased IC-stimulated TNFα secretion. These findings correlated significantly with different disease activity markers. Furthermore, sFcRs were elevated in the patient plasma, and sCD64 was specific for RA (compared with a reference group of patients with active psoriatic arthritis). Following treatment, immunoglobulins and sFcR levels were reduced, whereas membrane CD64 was only decreased in patients with good response to treatment.

CONCLUSIONS

Early RA patients display increased membrane and soluble CD64 and an impaired FcγR function correlating with joint disease activity. Beneficial responses of anti-rheumatic treatment in patients reduce CD64. These data suggest sCD64 as an important objective biomarker in RA.

Up-regulation of CD64-expressing monocytes with impaired FcγR function reflects disease activity in polyarticular psoriatic arthritis

OBJECTIVES

The aim of this study was to assess monocyte Fc receptor (FcR) status and function in patients with active psoriatic arthritis (PsA) in relation to healthy controls (HC) and to disease activity.

METHOD

The study population comprised 23 patients with active polyarticular PsA and 33 age- and gender-matched HC. Immunoglobulin (Ig) levels, inflammatory laboratory parameters, patient-reported outcomes of joint disease activity, skin scoring (Psoriasis Area and Severity Index, PASI), and joint status were determined in the patients. Monocytes were analysed for the expression of FcRs for IgG (FcγR) class I (CD64), IIa (CD32a), IIb (CD32b), and III (CD16), the FcR for IgA (FcαR) (CD89), and surface-bound IgG. The monocytic FcγR function was assessed by evaluating IgG immune complex (IC) binding and tumour necrosis factor (TNF)-α production following IgG-IC stimulation. The monocytes were further subdivided and analysed according to their CD14 and CD16 expression.

RESULTS

The PsA patients presented elevated serum levels of IgG1, 2, and 3 and increased numbers of CD64(+) monocytes. Furthermore, the PsA monocytes exhibited increased cell-bound IgG, and the FcγR function was affected in terms of reduced IgG-IC-mediated TNF-α release. These findings correlated significantly with different markers of joint disease activity. PsA was also accompanied by an increase in the CD16 low-expressing monocyte subset.

CONCLUSIONS

An intensified humoral immune response affects monocytes and their FcR status in active polyarticular PsA. The up-regulated CD64(+) monocytes seem to be have an important role in psoriatic joint inflammation. These cells may prove to be a useful target in future PsA therapeutic interventions.

Neutrophil CD64 expression as a diagnostic marker for sepsis in adult patients: a meta-analysis

INTRODUCTION

Neutrophil CD64 (nCD64) expression appears to be a promising marker of bacterial infections. The aim of this meta-analysis was to assess the accuracy of nCD64 expression for the diagnosis of sepsis in critically ill adult patients.

METHODS

We systematically searched PubMed, Embase, ISI Web of Knowledge, and the Cochrane Library for literature published between database inception and 19 May 2014, as well as reference lists of identified primary studies. Studies were included if they included assessment of the accuracy of nCD64 expression for sepsis diagnosis in adult patients and provided sufficient information to construct a 2×2 contingency table.

RESULTS

A total of 8 studies comprising 1986 patients fulfilled the inclusion criteria for the final analysis. The pooled sensitivity and specificity were 0.76 (95 % confidence interval [CI], 0.73-0.78) and 0.85 (95 % CI, 0.82-0.87), respectively. The positive likelihood ratio, negative likelihood ratio and diagnostic odds ratio were 8.15 (95 % CI, 3.82-17.36), 0.16 (95 % CI, 0.09-0.30), and 60.41 (95 % CI, 15.87-229.90), respectively. The area under the summary receiver operating characteristic curve of nCD64 expression with Q* value were 0.95 (Q* =0.89).

CONCLUSIONS

On the basis of our meta-analysis, nCD64 expression is a helpful marker for early diagnosis of sepsis in critically ill patients. The results of the test should not be used alone to diagnose sepsis, but instead should be interpreted in combination with medical history, physical examination, and other test results.

Neutrophil CD64 level as a rapid and promising diagnostic tool for infectious diseases in elderly patients

AIM

We examined the utility of the neutrophil CD64 level as a rapid and sensitive diagnostic marker for infections in febrile aged patients.

METHODS

The expression level of CD64 per neutrophil was quantitatively measured with flow cytometry using a QuantiBrite kit in samples from febrile (aged >65 years) patients. Information about the presence or absence of infectious disease was retrospectively obtained from each patient's medical record in which attending physicians were obliged to write down a tentative diagnosis after resolution of manifestations.

RESULTS

With receiver operating characteristic curve evaluation using the results, a CD64 level >2000 molecules per neutrophil was sensitive and specific for detecting infection. Among 102 patients suspected of having infection, 72 patients were diagnosed with infectious diseases, and 30 patients had non-infectious diseases. The sensitivity and specificity of determination of the neutrophil CD64 level were 88% and 63%, respectively. However, considering the high frequency of infections in elderly patients (71% in the present study), the post-test probability reached as high as 93%. The positive likelihood ratio was 2.4, and the negative likelihood ratio was 0.2.

CONCLUSIONS

Considering the frequency of infectious diseases in elderly patients, determination of the neutrophil CD64 level helps detect infectious diseases.

Interferon-gamma Therapy Activates Human Monocytes for Enhanced Phagocytosis ofMycobacterium aviumComplex in HIV-Infected Individuals

Defective immunological function of cells of the macrophage lineage contributes to the pathogenesis of HIV-1 infection. Because monocyte/macrophage function is enhanced by cytokines such as interferon-gamma (IFN-gamma), the use of this immunomodulator is of potential clinical interest as adjunctive immunotherapy in immunosuppressed individuals. In this study, we show that adjunctive IFN-gamma treatment in an HIV-infected individual with Mycobacterium avium complex (MAC) infection increased phagocytosis of MAC by blood monocytes when compared to cells from an HIV-infected patient who was receiving standard chemotherapy alone. Enhanced phagocytic efficiency resulting from IFN-gamma therapy was associated with increased surface expression of MHC II (HLA-DR), a phagocytic receptor (CD16), and the activation marker (CD69), although the levels of activation markers were dissimilar at baseline in the two participants. These results imply that IFN-gamma may be useful in restoring antimycobacterial function in immunosuppressed patients.

Automated analysis of flow cytometric data for measuring neutrophil CD64 expression using a multi-instrument compatible probability state model

BACKGROUND

Leuko64™ (Trillium Diagnostics) is a flow cytometric assay that measures neutrophil CD64 expression and serves as an in vitro indicator of infection/sepsis or the presence of a systemic acute inflammatory response. Leuko64 assay currently utilizes QuantiCALC, a semiautomated software that employs cluster algorithms to define cell populations. The software reduces subjective gating decisions, resulting in interanalyst variability of <5%. We evaluated a completely automated approach to measuring neutrophil CD64 expression using GemStone™ (Verity Software House) and probability state modeling (PSM).

METHODS

Four hundred and fifty-seven human blood samples were processed using the Leuko64 assay. Samples were analyzed on four different flow cytometer models: BD FACSCanto II, BD FACScan, BC Gallios/Navios, and BC FC500. A probability state model was designed to identify calibration beads and three leukocyte subpopulations based on differences in intensity levels of several parameters. PSM automatically calculates CD64 index values for each cell population using equations programmed into the model. GemStone software uses PSM that requires no operator intervention, thus totally automating data analysis and internal quality control flagging. Expert analysis with the predicate method (QuantiCALC) was performed. Interanalyst precision was evaluated for both methods of data analysis.

RESULTS

PSM with GemStone correlates well with the expert manual analysis, r(2) = 0.99675 for the neutrophil CD64 index values with no intermethod bias detected. The average interanalyst imprecision for the QuantiCALC method was 1.06% (range 0.00-7.94%), which was reduced to 0.00% with the GemStone PSM. The operator-to-operator agreement in GemStone was a perfect correlation, r(2) = 1.000.

CONCLUSION

Automated quantification of CD64 index values produced results that strongly correlate with expert analysis using a standard gate-based data analysis method. PSM successfully evaluated flow cytometric data generated by multiple instruments across multiple lots of the Leuko64 kit in all 457 cases. The probability-based method provides greater objectivity, higher data analysis speed, and allows for greater precision for in vitro diagnostic flow cytometric assays.

Characterization of the biological anti-staphylococcal functionality of hUK-66 IgG1, a humanized monoclonal antibody as substantial component for an immunotherapeutic approach

Multi-antigen immunotherapy approaches against Staphylococcus aureus are expected to have the best chance of clinical success when used in combinatorial therapy, potentially incorporating opsonic killing of bacteria and toxin neutralization. We recently reported the development of a murine monoclonal antibody specific for the immunodominant staphylococcal antigen A (IsaA), which showed highly efficient staphylococcal killing in experimental infection models of S. aureus. If IsaA-specific antibodies are to be used as a component of combination therapy in humans, the binding specificity and biological activity of the humanized variant must be preserved. Here, we describe the functional characterization of a humanized monoclonal IgG1 variant designated, hUK-66. The humanized antibody showed comparable binding kinetics to those of its murine parent, and recognized the target antigen IsaA on the surface of clinically relevant S. aureus lineages. Furthermore, hUK-66 enhances the killing of S. aureus in whole blood (a physiological environment) samples from healthy subjects and patients prone to staphylococcal infections such as diabetes and dialysis patients, and patients with generalized artery occlusive disease indicating no interference with already present natural antibodies. Taken together, these data indicate that hUK-66 mediates bacterial killing even in high risk patients and thus, could play a role for immunotherapy strategies to combat severe S. aureus infections.

The assessment of neutrophil CD64 count as an early warning marker of joint replacement infection

120,000 hip and knee replacements are performed each year in the UK and more than 1 % of these require revision surgery due to infection. Current diagnostic tests used to diagnose infection of joint replacements, including the current gold standard C-reactive protein, which offers poor specificity when diagnosing infection in the post-operative period. In the post-operative period these tests are unable to differentiate between physiological inflammation and infection of the replacement. Early treatment through antibiotic and washout therapy is essential to eradicate infection, saving the patient and the NHS the stress of revision surgery, which offers a much poorer prognosis than the original operative procedure. Thus, a superior marker is required and CD64 has been proposed to fulfil the necessary requirements of an effective marker. Data from several studies utilising a flow cytometer support the view that CD64 is firstly, a good marker of systemic infection and secondly, when studied in conjunction with musculoskeletal infections alone, is a sensitive and specific marker of this type of infection. However, meta-analysis of studies in this field concludes that more highly powered studies are needed before definite conclusions can be drawn. Despite this, the studies do portray a strong case for CD64 being the future of diagnosis of post-operative infection.

Diagnostic accuracy of neutrophil CD64 expression in neonatal infection: A meta-analysis

Objective

*Liu-Qun Jia and Yong-Chun Shen contributed equally to this work and are joint first authors. The aim of the present study was to establish the predictive values of neutrophil CD64 expression in diagnosing neonatal infection.

Methods

A comprehensive search of the PubMed and Embase® literature databases identified outcome data from published studies estimating the diagnostic accuracy of neutrophil CD64 expression for neonatal infection. Summary estimates for sensitivity, specificity, diagnostic odds ratios (DOR) and the area under the summary receiver operating characteristic curve (AUC) were calculated using a bivariate random-effects approach.

Results

Twelve studies including 1915 neonates were analysed. Summary estimates (95% confidence intervals) for CD64 expression in the diagnosis of neonatal infection were: sensitivity, 0.78 (0.75, 0.81); specificity, 0.81 (0.78, 0.83); DOR, 21.27 (11.71, 38.65); positive-likelihood ratio, 4.53 (3.22, 6.36); negative-likelihood ratio, 0.23 (0.14, 0.37); AUC, 0.89.

Conclusions

Neutrophil CD64 expression can be used as an additional test in the diagnosis of neonatal infection. Results of a CD64 assay should not be used alone to diagnose such infections, but should be interpreted in combination with other test results and clinical findings.

Neutrophil CD64 expression as a biomarker in the early diagnosis of bacterial infection: a meta-analysis

BACKGROUND

Neutrophil CD64 expression is widely reported as an efficacious biomarker to differentiate infected patients from other non-infected patients. This meta-analysis was conducted to comprehensively and quantitatively summarize the accuracy of neutrophil CD64 in the early diagnosis of bacterial infection.

METHODS

A systematic review of related studies was conducted, and the sensitivity, specificity, and other data about the accuracy of CD64 expression on neutrophils were pooled using random effects models with 95% confidence intervals (CI) as the effect measurements. Summary receiver operating characteristic (SROC) curves and the Q* value were also calculated in the meta-analysis. Heterogeneity was tested, as well as the publication bias. Potential sources of heterogeneity were explored by assessing whether or not certain covariates significantly influenced the summary diagnostic odds ratio (SDOR).

RESULTS

A total of 26 studies including 3944 patients met the inclusion criteria for the final analysis. The summary estimate was 0.76 (95% CI 0.74-0.78) for sensitivity and 0.85 (95% CI 0.83-0.86) for specificity. The positive likelihood ratio (PLR), negative likelihood ratio (NLR), SDOR, and area under the SROC of neutrophil CD64 expression with Q* value were 6.67 (95% CI 4.67-9.53), 0.24 (95% CI 0.18-0.31), 34.29 (95% CI 19.59-60.01), and 0.92 (Q*=0.85), respectively. The pooled data from the included studies had high heterogeneity and the Egger test suggested a publication bias.

CONCLUSIONS

On the basis of our meta-analysis, neutrophil CD64 expression could be a promising and meaningful biomarker for diagnosing bacterial infection. Nevertheless, more large prospective studies should be carried out before the neutrophil CD64 test is used widely in the clinical setting because of the various cut-off values.

Innate immune deficiency of extremely premature neonates can be reversed by interferon-γ

BACKGROUND

Bacterial sepsis is a major threat in neonates born prematurely, and is associated with elevated morbidity and mortality. Little is known on the innate immune response to bacteria among extremely premature infants.

METHODOLOGY/PRINCIPAL FINDINGS

We compared innate immune functions to bacteria commonly causing sepsis in 21 infants of less than 28 wks of gestational age, 24 infants born between 28 and 32 wks of gestational age, 25 term newborns and 20 healthy adults. Levels of surface expression of innate immune receptors (CD14, TLR2, TLR4, and MD-2) for Gram-positive and Gram-negative bacteria were measured in cord blood leukocytes at the time of birth. The cytokine response to bacteria of those leukocytes as well as plasma-dependent opsonophagocytosis of bacteria by target leukocytes was also measured in the presence or absence of interferon-γ. Leukocytes from extremely premature infants expressed very low levels of receptors important for bacterial recognition. Leukocyte inflammatory responses to bacteria and opsonophagocytic activity of plasma from premature infants were also severely impaired compared to term newborns or adults. These innate immune defects could be corrected when blood from premature infants was incubated ex vivo 12 hrs with interferon-γ.

CONCLUSION/SIGNIFICANCE

Premature infants display markedly impaired innate immune functions, which likely account for their propensity to develop bacterial sepsis during the neonatal period. The fetal innate immune response progressively matures in the last three months in utero. Ex vivo treatment of leukocytes from premature neonates with interferon-γ reversed their innate immune responses deficiency to bacteria. These data represent a promising proof-of-concept to treat premature newborns at the time of delivery with pharmacological agents aimed at maturing innate immune responses in order to prevent neonatal sepsis.

Human IgG isotypes and activating Fcγ receptors in the interaction of Salmonella enterica serovar Typhimurium with phagocytic cells

Several classes and multiple subclasses of immunoglobulins are produced towards protein and polysaccharide antigens in response to Salmonella infection and play a key role in protection against systemic disease. The targeting of Salmonella to Fc receptors (FcR) on phagocytes is a key step in the antibody-mediated antibacterial functions of host cells. We wished to compare the relative efficiency of different human IgG subclasses, which targeted the Salmonella enterica OmpA surface protein in modulating the interaction of bacteria with human phagocytes. To this end, we developed a novel system by tagging OmpA with a foreign CD52 mimotope (TSSPSAD) and opsonizing the bacteria with a panel of humanized CD52 antibodies that share the same antigen-binding V-region, but have constant regions of different subclasses. Our data revealed that opsonization with all the IgG subclasses increases Salmonella uptake by human phagocytes. IgG3 resulted in the highest level of bacterial uptake and the highest average bacterial load per infected cell, which was closely followed by IgG1, then IgG4 and lastly IgG2. Phagocytosis mediated by IgG1, IgG3 and IgG4 had a higher dependency on FcγRI than FcγRIIA, whereas IgG2-mediated phagocytosis required FcγRIIA more than FcγRI. The results show that IgG binding to OmpA increases the uptake of Salmonella by human phagocytic cells and that the efficiency of this process depends both on the subclass of the IgG and the type of FcR that is available for antibody binding.

Neutrophil CD64: diagnostic accuracy and prognostic value in patients presenting to the emergency department

The purpose of this study was to evaluate the diagnostic accuracy and prognostic value of neutrophil CD64 expression for bacterial infection in febrile adult patients presenting to our hospital emergency department. We prospectively included 132 patients with fever ≥ 38ºC (≥ 100.4ºF) during the last 24 hours and we measured CD64 expression on neutrophils the day after admission at the emergency department. We followed the patients until full recovery or death. There were 115 (87%) patients with bacterial infection and 108 (94%) of them survived. There were 17 (13%) patients without bacterial infection and 12 (71%) of them survived. Patients with bacterial infection and patients who survived showed a CD64 index higher when compared with patients without bacterial infection and patients who died, respectively (3.7 ± 3.2 vs. 2.5 ± 2.3; p = 0.03; and 3.7 ± 3.1 vs. 1.7 ± 0.6; p = 0.002; Mann-Whitney U test). The receiver operating characteristic (ROC) curve analysis for detecting bacterial infection and predicting survival with the CD64 index showed an area under curve (AUC) of 0.66 (95% CI, 0.52-0.8; p = 0.03) and 0.71 (95% CI, 0.57-0.85; p = 0.01), respectively. Diagnostic accuracy and prognostic value of CD64 expression was good in adult patients with fever.

Impaired phagocytosis of apoptotic cells by macrophages in chronic granulomatous disease is reversed by IFN-γ in a nitric oxide-dependent manner

Immunodeficiency in chronic granulomatous disease (CGD) is well characterized. Less understood are exaggerated sterile inflammation and autoimmunity associated with CGD. Impaired recognition and clearance of apoptotic cells resulting in their disintegration may contribute to CGD inflammation. We hypothesized that priming of macrophages (Ms) with IFN-γ would enhance impaired engulfment of apoptotic cells in CGD. Diverse M populations from CGD (gp91(phox)(-/-)) and wild-type mice, as well as human Ms differentiated from monocytes and promyelocytic leukemia PLB-985 cells (with and without mutation of the gp91(phox)), demonstrated enhanced engulfment of apoptotic cells in response to IFN-γ priming. Priming with IFN-γ was also associated with increased uptake of Ig-opsonized targets, latex beads, and fluid phase markers, and it was accompanied by activation of the Rho GTPase Rac. Enhanced Rac activation and phagocytosis following IFN-γ priming were dependent on NO production via inducible NO synthase and activation of protein kinase G. Notably, endogenous production of TNF-α in response to IFN-γ priming was critically required for inducible NO synthase upregulation, NO production, Rac activation, and enhanced phagocytosis. Treatment of CGD mice with IFN-γ also enhanced uptake of apoptotic cells by M in vivo via the signaling pathway. Importantly, during acute sterile peritonitis, IFN-γ treatment reduced excess accumulation of apoptotic neutrophils and enhanced phagocytosis by CGD Ms. These data support the hypothesis that in addition to correcting immunodeficiency in CGD, IFN-γ priming of Ms restores clearance of apoptotic cells and may thereby contribute to resolution of exaggerated CGD inflammation.