Human B1 cells in umbilical cord and adult peripheral blood express the novel phenotype CD20+CD27+CD43+CD70−

Human B1 cells consist of CD20+CD27+CD43+CD70− cells bearing a skewed B cell receptor repertoire, and are present in umbilical cord and adult peripheral blood

A CD25− Positive Population of Activated B1 Cells Expresses LIFR and Responds to LIF

B1 B cells defend against infectious microorganisms by spontaneous secretion of broadly reactive “natural” immunoglobulin that appears in the absence of immunization. Among many distinguishing characteristics, B1 B cells display evidence of activation that includes phosphorylated STAT3. In order to identify the origin of pSTAT3 we examined interleukin-2 receptor (IL-2R) expression on B1 cells. We found that some (about 1/5) B1a cells express the IL-2R α chain, CD25. Although lacking CD122 and unresponsive to IL-2, B1a cells marked by CD25 express increased levels of activated signaling intermediates, interruption of which results in diminished CD25. Further, CD25+ B1a cells contain most of the pSTAT3 found in the B1a population as a whole. Moreover, CD25+ B1a cells express leukemia inhibitory factor receptor (LIFR), and respond to LIF by upregulating pSTAT3. Together, these results define a new subset of B1a cells that is marked by activation-dependent CD25 expression, expresses substantial amounts of activated STAT3, and contains a functional LIFR

Natural Antibodies in Health and Disease

Natural antibodies (NAbs) are found in normal individuals in the absence of exogenous antigenic stimulation. Natural antibodies rapidly recognize and protect against pathogens that have not been previously encountered. NAbs also cross-react with several self-antigens, which, besides their role as a first line of defense against pathogens, affords them the ability to perform important housekeeping functions in healthy organisms. Such housekeeping functions include the clearance of oxidized damaged structures and/or apoptotic cells, which prevents the induction of pro-inflammatory effects. In addition, NAbs play a role in preventing the expansion of specific auto-reactive clones, thereby behaving as regulatory elements in acute or chronic inflammation. To maintain the non-pathogenic balance between the dual pathogen/self-antigen cross-reactivities of NAbs, a strict regulation in NAb secretion and function is necessary to avoid autoimmune disease. Actually, some of the NAbs related auto-reactivities, such as anti-DNA and anti-MOG, have been associated with autoimmunity. Furthermore, NAbs have been shown to bind to ‘neo-self’ carbohydrate antigens on glycolipids and glycoproteins found on malignant but not normal cells, which suggests NAbs may take part in tumor immunosurveillance. Many aspects regarding NAbs have yet to be studied in more detail: the reactivity and function of NAbs in health and disease, the behavior of the NAb repertoire with increasing age, the regulation of natural antibody production and auto-reactivity, the ways to specifically activate NAbs producing cells with desired specificities, the characteristics of human NAbs, among others. This special topics eBook consists of a number of articles exploring the cells that produce NAbs as well as the characteristics, function, specificity, and/or the role of natural antibodies in health and disease

B-CD8+ T Cell Interactions in the Anti-Idiotypic Response against a Self-Antibody

P3 is a murine, germline, IgM mAb that recognizes N-glycolylated gangliosides and other self-antigens. This antibody is able to induce an anti-idiotypic IgG response and B-T idiotypic cascade, even in the absence of any adjuvant or carrier protein. P3 mAb immunization induces the expression of activation markers in a significant percentage of B-1a cells in vivo. Interestingly, transfer of both B-1a and B-2 to BALB/Xid mice was required to recover anti-P3 IgG response in this model. In fact, P3 mAb activated B-2 cells, in vitro, inducing secretion of IFN-γ and IL-4, although this activation was not detected ex vivo. Interestingly, naïve CD8+ T cells increased the expression of activation markers and IFN-γ secretion in the presence of B-1a cells isolated from P3 mAb-immunized mice, even without in vitro restimulation. In contrast, B-2 cells were able to stimulate CD8+ T cells only if P3 was added in vitro. Using bioinformatics, a MHC class I-binding peptide from P3 VH region was identified. P3 mAb was able to induce a specific CTL response in vivo against cells presenting this peptide. Both humoral and CTL anti-idiotypic responses could be mechanisms to protect against the self-reactive antibody, contributing to keeping the tolerance to self-antigens

B-1a cells protect mice from sepsis-induced acute lung injury

Abstract Background Sepsis morbidity and mortality are aggravated by acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Mouse B-1a cells are a phenotypically and functionally unique sub-population of B cells, providing immediate protection against infection by releasing natural antibodies and immunomodulatory molecules. We hypothesize that B-1a cells ameliorate sepsis-induced ALI. Methods Sepsis was induced in C57BL/6 mice by cecal ligation and puncture (CLP). PBS or B-1a cells were adoptively transferred into the septic mice intraperitoneally. After 20 h of CLP, lungs were harvested and assessed by PCR and ELISA for pro-inflammatory cytokines (IL-6, IL-1β) and chemokine (MIP-2) expression, by histology for injury, by TUNEL and cleaved caspase-3 for apoptosis, and by myeloperoxidase (MPO) assay for neutrophil infiltration. Results We found that septic mice adoptively transferred with B-1a cells significantly decreased the mRNA and protein levels of IL-6, IL-1β and MIP-2 in the lungs compared to PBS-treated mice. Mice treated with B-1a cells showed dramatic improvement in lung injury compared to PBS-treated mice after sepsis. We found apoptosis in the lungs was significantly inhibited in B-1a cell injected mice compared to PBS-treated mice after sepsis. B-1a cell treatment significantly down-regulated MPO levels in the lungs compared to PBS-treated mice in sepsis. The protective outcomes of B-1a cells in ALI was further confirmed by using B-1a cell deficient CD19−/− mice, which showed significant increase in the lung injury scores following sepsis as compared to WT mice. Conclusions Our results demonstrate a novel therapeutic potential of B-1a cells to treat sepsis-induced ALI