Newly discovered innate response activator B cells: crucial responders against microbial sepsis

The emerging roles and therapeutic potential of B cells in sepsis

Sepsis is a life-threatening syndrome caused by anomalous host response to infection. The pathogenesis of sepsis is complex, and immune dysfunction is the central link in its occurrence and development. The sepsis immune response is not a local and transient process but a complex and continuous process involving all major cell types of innate and adaptive immunity. B cells are traditionally studied for their ability to produce antibodies in the context of mediating humoral immunity. However, over the past few years, B cells have been increasingly recognized as key modulators of adaptive and innate immunity, and they can participate in immune responses by presenting antigens, producing cytokines, and modulating other immune cells. Recently, increasing evidence links B-cell dysfunction to mechanisms of immune derangement in sepsis, which has drawn attention to the powerful properties of this unique immune cell type in sepsis. Here, we reviewed the dynamic alterations of B cells and their novel roles in animal models and patients with sepsis, and provided new perspectives for therapeutic strategies targeting B cells in sepsis.

The Forgotten Brother: The Innate-like B1 Cell in Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative disease of the central nervous system (CNS), traditionally considered a chronic autoimmune attack against the insulating myelin sheaths around axons. However, the exact etiology has not been identified and is likely multi-factorial. Recently, evidence has been accumulating that implies that autoimmune processes underlying MS may, in fact, be triggered by pathological processes initiated within the CNS. This review focuses on a relatively unexplored immune cell-the "innate-like" B1 lymphocyte. The B1 cell is a primary-natural-antibody- and anti-inflammatory-cytokine-producing cell present in the healthy brain. It has been recently shown that its frequency and function may differ between MS patients and healthy controls, but its exact involvement in the MS pathogenic process remains obscure. In this review, we propose that this enigmatic cell may play a more prominent role in MS pathology than ever imagined. We aim to shed light on the human B1 cell in health and disease, and how dysregulation in its delicate homeostatic role could impact MS. Furthermore, novel therapeutic avenues to restore B1 cells' beneficial functions will be proposed.

Innate-like B cell subsets during immune responses: Beyond antibody production

B lymphocytes are recognized for their crucial role in the adaptive immunity since they represent the only leukocyte lineage capable of differentiating into Ab-secreting cells. However, it has been demonstrated that these lymphocytes can exert several Ab-independent functions, including engulfing and processing Ags for presentation to T cells, secreting soluble mediators, providing co-stimulatory signals, and even participating in lymphoid tissues development. Beyond that, several reports claiming the existence of multiple B cell subsets contributing directly to innate immune responses have appeared. These "innate-like" B lymphocytes, whose phenotype, development pathways, tissue distribution, and functions are in most cases notoriously different from those of conventional B cells, are crucial to early protective responses against pathogens by exerting "crossover" defensive strategies that blur the established boundaries of innate and adaptive branches of immunity. Examples of these mechanisms include the rapid secretion of the polyspecific natural Abs, increased susceptibility to innate receptors-mediated activation, cytokine secretion, downstream priming of other innate cells, usage of specific variable immunoglobulin gene-segments, and other features. As these new insights emerge, it is becoming preponderant to redefine the functionality of B cells beyond their classical adaptive-immune tasks.

Inflammasome function in monocyte subsets and a risk of late-onset sepsis in preterm very low birth weight neonates

BACKGROUND

Immature immune systems predispose very low birth weight (VLBW) neonates to systemic infections in early life. Defective inflammasome function may increase a neonate's susceptibility to late-onset sepsis (LOS).

METHODS

Blood samples were taken on the 5^th day of life (DOL) for all VLBW neonates (non-LOS and before-LOS groups; N.=76), and within 24 hours of sepsis onset (LOS group; N.=39). Monocyte (MO) subsets and intracellular interleukin-1β (IL-1β) expression were analyzed using flow cytometry. Inflammasome function, defined as level of IL-1β and interleukin-18 (IL-18) was measured with enzyme-linked immunosorbent assay. IRA B cells were reported as a fraction of all B cells.

RESULTS

Stimulation of classical MO in non-LOS cells demonstrated a higher expression of intracellular IL-1β in comparison to MO from before LOS group. Serum from the LOS group revealed a higher level of IL-18. Stimulation of mononuclear cultures from samples taken during LOS resulted in significantly increased supernatant level of IL-1β and IL-18 in comparison to samples taken on 5^th DOL. No changes in the levels of IRA B cells were detected with the onset of sepsis.

CONCLUSIONS

We did not observe a difference in the functioning of the inflammasome within monocytes taken on 5^th DOL from premature VLBW neonates. Furthermore, there was no observable change in the IRA B cells of the septic and non-septic groups. The decreased expression of intracellular IL-1β within classical MO of the before-LOS group may be an independent risk factor for LOS development.

Role of circulating lymphocytes in patients with sepsis

Sepsis is a systemic inflammatory response syndrome due to infection. The incidence rate is estimated to be up to 19 million cases worldwide per year and the number of cases is rising. Infection triggers a complex and prolonged host response, in which both the innate and adaptive immune response are involved. The disturbance of immune system cells plays a key role in the induction of abnormal levels of immunoregulatory molecules. Furthermore, the involvement of effector immune system cells also impairs the host response to the infective agents and tissue damage. Recently, postmortem studies of patients who died of sepsis have provided important insights into why septic patients die and showed an extensive depletion of CD4 and CD8 lymphocytes and they found that circulating blood cells showed similar findings. Thus, the knowledge of the characterization of circulating lymphocyte abnormalities is relevant for the understanding of the sepsis pathophysiology. In addition, monitoring the immune response in sepsis, including circulating lymphocyte subsets count, appears to be potential biomarker for predicting the clinical outcome of the patient. This paper analyzes the lymphocyte involvement and dysfunction found in patients with sepsis and new opportunities to prevent sepsis and guide therapeutic intervention have been revealed.

Monocyte heterogeneity in cardiovascular disease

Only a few decades ago, students of the pathophysiology of cardiovascular disease paid little heed to the involvement of inflammation and immunity. Multiple lines of evidence now point to the participation of innate and adaptive immunity and inflammatory signaling in a variety of cardiovascular conditions. Hence, interest has burgeoned in this intersection. This review will focus on the contribution of innate immunity to both acute injury to the heart muscle itself, notably myocardial infarction, and to chronic inflammation in the artery wall, namely atherosclerosis, the cause of most myocardial infarctions. Our discussion of the operation of innate immunity in cardiovascular diseases will focus on functions of the mononuclear phagocytes, with special attention to emerging data regarding the participation of different functional subsets of these cells in cardiovascular pathophysiology.

Early alterations of B cells in patients with septic shock

Introduction

It has recently been proposed that B lymphocytes are involved in sepsis pathogenesis. The goal of this study is to investigate potential abnormalities in a subset distribution and activation of circulating B lymphocytes in patients with septic shock.

Methods

This observational prospective study was conducted in a medical-surgical ICU. All patients with septic shock were eligible for inclusion. B-cell phenotypes (CD19+CD69+, CD19+CD23+, CD19+CD5+, CD19+CD80, CD19+CD86+, CD19+CD40 and CD19+CD95+) were assessed by quantitative flow cytometry upon admission to the ICU and 3, 7, 14 and 28 d later.

Results

Fifty-two patients were included. Thirty-six healthy volunteers matched for age and sex were used as controls. The patients had lymphopenia that was maintained during 28 d of follow-up. In patients with septic shock who died, the percentage of CD19+CD23+ was lower during the 7 d of follow-up than it was in survival patients. Moreover, the percentage of CD80+ and CD95+ expression on B cells was higher in patients who died than in survivors. Receiver operating characteristic curve analysis showed that a CD19+CD23+ value of 64.6% at ICU admission enabled discrimination between survivors and nonsurvivors with a sensitivity of 90.9% and a specificity of 80.0% (P = 0.0001).

Conclusions

Patients with septic shock who survive and those who don't have different patterns of abnormalities in circulating B lymphocytes. At ICU admission, a low percentage of CD23+ and a high of CD80+ and CD95+ on B cells were associated with increased mortality of patients with septic shock. Moreover, a drop in circulating B cells persisted during 28 d of ICU follow-up.