How B cells remember? A sophisticated cytoplasmic tail of mIgG is pivotal for the enhanced transmembrane signaling of IgG-switched memory B cells

Mechanical control of antigen detection and discrimination by T and B cell receptors

The adaptive immune response is orchestrated by just two cell types, T cells and B cells. Both cells possess the remarkable ability to recognize virtually any antigen through their respective antigen receptors-the T cell receptor (TCR) and B cell receptor (BCR). Despite extensive investigations into the biochemical signaling events triggered by antigen recognition in these cells, our ability to predict or control the outcome of T and B cell activation remains elusive. This challenge is compounded by the sensitivity of T and B cells to the biophysical properties of antigens and the cells presenting them-a phenomenon we are just beginning to understand. Recent insights underscore the central role of mechanical forces in this process, governing the conformation, signaling activity, and spatial organization of TCRs and BCRs within the cell membrane, ultimately eliciting distinct cellular responses. Traditionally, T cells and B cells have been studied independently, with researchers working in parallel to decipher the mechanisms of activation. While these investigations have unveiled many overlaps in how these cell types sense and respond to antigens, notable differences exist. To fully grasp their biology and harness it for therapeutic purposes, these distinctions must be considered. This review compares and contrasts the TCR and BCR, placing emphasis on the role of mechanical force in regulating the activity of both receptors to shape cellular and humoral adaptive immune responses.

Immunization with a peptide mimicking lipoteichoic acid induces memory B cells in BALB/c mice

BACKGROUND

There is an urgent clinical need for developing novel immunoprophylaxis and immunotherapy strategies against Staphylococcus aureus (S. aureus). In our previous work, immunization with a tetra-branched multiple antigenic peptide, named MAP2-3 that mimics lipoteichoic acid, a cell wall component of S. aureus, successfully induced a humoral immune response and protected BALB/c mice against S. aureus systemic infection. In this study, we further investigated whether vaccination with MAP2-3 can elicit immunologic memory.

METHODS

BALB/c mice were immunized with MAP2-3 five times. After one month of the last vaccination, mice were challenged with heat-killed S. aureus via intraperitoneal injection. After a 7-day inoculation, the percentage of plasma cells, memory B cells, effector memory T cells, and follicular helper T cells were detected by flow cytometry. The levels of IL-6, IL-21, IL-2, and IFN-γ were measured by real-time PCR and ELISA. Flow cytometry results were compared by using one-way ANOVA or Mann-Whitney test, real-time PCR results were compared by using one-way ANOVA, and ELISA results were compared by using one-way ANOVA or student's t-test.

RESULTS

The percentage of plasma cells and memory B cells in the spleen and bone marrow from the MAP2-3 immunized mice was significantly higher than that from the control mice. The percentage of effector memory T cells in spleens and lymphoid nodes as well as follicular helper T cells in spleens from the MAP2-3 immunized mice were also higher. Moreover, the levels of IL-6 and IL-21, two critical cytokines for the development of memory B cells, were significantly higher in the isolated splenocytes from immunized mice after lipoteichoic acid stimulation.

CONCLUSIONS

Immunization with MAP2-3 can efficiently induce memory B cells and memory T cells.

Identification of a novel amphioxus leucine-rich repeat receptor involved in phagocytosis reveals a role for Slit2-N-type LRR in bacterial elimination

The basal chordate amphioxus is a model for tracing the origin and evolution of vertebrate immunity. To explore the evolution of immunoreceptor signaling pathways, we searched the associated receptors of the amphioxus B. belcheri (Bb) homolog of immunoreceptor signaling adaptor protein Grb2. Mass-spectrum analysis of BbGrb2 immunoprecipitates from B. belcheri intestine lysates revealed a folate receptor (FR) domain- and leucine-rich repeat (LRR)-containing protein (FrLRR). Sequence and structural analysis showed that FrLRR is a membrane protein with a predicted curved solenoid structure. The N-terminal Fr domain contains very few folate-binding sites; the following LRR region is a Slit2-type LRR, and a GPI-anchored site was predicted at the C-terminus. RT-PCR analysis showed FrLRR is a transcription-mediated fusion gene of BbFR-like and BbSlit2-N-like genes. Genomic DNA structure analysis implied the B. belcheri FrLRR gene locus and the corresponding locus in B. floridae might be generated by exon shuffling of a Slit2-N-like gene into an FR gene. RT-qPCR, immunostaining and immunoblot results showed that FrLRR was primarily distributed in B. belcheri intestinal tissue. We further demonstrated that FrLRR localized to the cell membrane and lysosomes. Functionally, FrLRR mediated and promoted bacteria-binding and phagocytosis, and FrLRR antibody blocking or Grb2 knockdown inhibited FrLRR-mediated phagocytosis. Interestingly, we found that human Slit2-N (hSlit2-N) also mediated direct bacteria-binding and phagocytosis which was inhibited by Slit2-N antibody blocking or Grb2 knockdown. Together, these results indicate FrLRR and hSlit2-N may function as phagocytotic-receptors to promote phagocytosis through Grb2, implying the Slit2-N-type-LRR-containing proteins play a role in bacterial binding and elimination.

Assessment of adaptive immune responses of dairy cows with Burkholderia contaminans-induced mastitis

Burkholderia contaminans, an emerging pathogen related to cystic fibrosis, is known to cause potentially fatal infections in humans and ruminants, especially in immunocompromised individuals. However, the immune responses in cows following its infection have not been fully elucidated. In this study, T- and B-lymphocytes-mediated immune responses were evaluated in 15 B. contaminans-induced mastitis cows and 15 healthy cows with multi-parameter flow cytometry. The results showed that infection with B. contaminans was associated with a significant decrease in the number and percentage of B lymphocytes but with a significant increase in the proportion of IgG⁺CD27⁺ B lymphocytes. This indicated that humoral immune response may not be adequate to fight intracellular infection, which could contribute to the persistent bacterial infection. In addition, B. contaminans infection induced significant increase of γδ T cells and double positive (DP) CD4⁺CD8⁺ T cells but not CD4⁺ or CD8⁺ (single positive) T cells in blood. Phenotypic analysis showed that the percentages of activated WC1⁺ γδ T cells in peripheral blood were increased in the B. contaminans infected cows. Interestingly, intracellular cytokine staining showed that cattle naturally infected with B. contaminans exhibited multifunctional TNF-α⁺IFN-γ⁺IL-2⁺ B. contaminans-specific DP T cells. Our results, for the first time, revealed a potential role of IgG⁺CD27⁺ B cells, CD4⁺CD8⁺ T cells and WC1⁺ γδ T cells in the defense of B. contaminans-induced mastitis in cows.

Character of β-lymphocytes differentiation in women with hypertensive disorders during pregnancy

The aim of the work was to identify the features of B-lymphocyte differentiation in women with hypertensive disorders of various origins, to establish their relationship with indicators of the elastic properties of the vascular wall, and to develop additional diagnostic criteria for the severity of preeclampsia. We examined 193 women at 24-40 weeks of gestation. Of these, 39 women with chronic arterial hypertension, 35 women with preeclampsia that developed against the background of chronic arterial hypertension, 55 with preeclampsia. The control group consisted of 64 women without hypertensive disorders. To assess the elastic properties of the vascular wall, a sphygmographic attachment of the "Poly-Spectrum-8" hardware-software complex ("Neurosoft" Ivanovo) was used. The relative content of B-lymphocytes (CD19 + and CD20 +), regulatory B-cells (CD20 + IL-10 +), switched (CD19 + CD27 + IgD-) and non-switched (CD19 + CD27 + IgD +) memory cells, plasma cells (CD19 + CD20-CD38 +) in the general population of B-lymphocytes was assessed by flow cytometry on a FACSCantoII flow cytometer using the FACS Diva program. Statistical analysis was carried out using the programs "Statistica for Windows 6.0", "Microsoft Excel 2010" and "MedCals". All subjects with hypertensive disorders showed an increase in the stiffness of the arteries of the muscular and elastic types, the most pronounced in the groups of patients with PE, the maximum in women with CAH and associated PE. An increased level of B1-lymphocytes in the peripheral blood is also noted in all hypertensive disorders. There were revealed positive correlations of high strength between: the level of CD20 + cells and the velocity of pulse wave propagation through the arteries of the muscular type (PWVm) in all groups with hypertensive disorders; the content of B1 cells and PWVM in moderate preeclampsia; level emory B-cells and PWV in elastic-type arteries in women with CAH and associated PE. The ROC analysis of the relative content of B1 cells in the general population of B lymphocytes and the content of IL-10-producing cells in the population of CD20 + lymphocytes (Breg) in women with moderate and severe PE revealed criteria for the differential diagnosis of preeclampsia of varying severity. The presence of hypertensive disorders of various origins is accompanied by a decrease in the elasticity of the arterial vascular wall, which is most pronounced in patients with CAH and associated PE. These changes are largely correlated with the level of B cells. As additional criteria for determining the severity of PE, the relative content of B1 cells and IL-10-producing cells in the population of Breg CD20 + lymphocytes can be used.

Genomic features of humoral immunity support tolerance model in Egyptian rousette bats

Bats asymptomatically harbor many viruses that can cause severe human diseases. The Egyptian rousette bat (ERB) is the only known reservoir for Marburgviruses and Sosuga virus, making it an exceptional animal model to study antiviral mechanisms in an asymptomatic host. With this goal in mind, we constructed and annotated the immunoglobulin heavy chain locus, finding an expansion on immunoglobulin variable genes associated with protective human antibodies to different viruses. We also annotated two functional and distinct immunoglobulin epsilon genes and four distinctive functional immunoglobulin gamma genes. We described the Fc receptor repertoire in ERBs, including features that may affect activation potential, and discovered the lack of evolutionary conserved short pentraxins. These findings reinforce the hypothesis that a differential threshold of regulation and/or absence of key immune mediators may promote tolerance and decrease inflammation in ERBs.

Structural and immunogenomic insights into B-cell receptor activation

B cells express B-cell receptors (BCRs) which recognize antigen to trigger signaling cascades for B-cell activation and subsequent antibody production. BCR activation has a crucial influence on B-cell fate. How BCR is activated upon encountering antigen remains to be solved, although tremendous progresses have been achieved in the past few years. Here, we summarize the models that have been proposed to explain BCR activation, including the cross-linking model, the conformation-induced oligomerization model, the dissociation activation model, and the conformational change model. Especially, we elucidate the partially resolved structures of antibodies and/or BCRs by far and discusse how these current structural and further immunogenomic messages and more importantly the future studies may shed light on the explanation of BCR activation and the relevant diseases in the case of dysregulation.

Growth of B Cell Receptor Microclusters Is Regulated by PIP2 and PIP3 Equilibrium and Dock2 Recruitment and Activation

The growth of B cell receptor (BCR) microclusters upon antigen stimulation drives B cell activation. Here, we show that PI3K-mediated PIP₃ production is required for the growth of BCR microclusters. This growth is likely inhibited by PTEN and dependent on its plasma membrane binding and lipid phosphatase activities. Mechanistically, we find that PIP₃-dependent recruitment and activation of a guanine nucleotide exchange factor, Dock2, is required for the sustained growth of BCR microclusters through remodeling of the F-actin cytoskeleton. As a consequence, Dock2 deficiency significantly disrupts the structure of the B cell immunological synapse. Finally, we find that primary B cells from systemic lupus erythematosus (SLE) patients exhibit more prominent BCR and PI3K microclusters than B cells from healthy controls. These results demonstrate the importance of a PI3K- and PTEN-governed PIP₂ and PIP₃ equilibrium in regulating the activation of B cells through Dock2-controlled growth of BCR microclusters.

A cold-blooded view of adaptive immunity

The adaptive immune system arose 500 million years ago in ectothermic (cold-blooded) vertebrates. Classically, the adaptive immune system has been defined by the presence of lymphocytes expressing recombination-activating gene (RAG)-dependent antigen receptors and the MHC. These features are found in all jawed vertebrates, including cartilaginous and bony fish, amphibians and reptiles and are most likely also found in the oldest class of jawed vertebrates, the extinct placoderms. However, with the discovery of an adaptive immune system in jawless fish based on an entirely different set of antigen receptors - the variable lymphocyte receptors - the divergence of T and B cells, and perhaps innate-like lymphocytes, goes back to the origin of all vertebrates. This Review explores how recent developments in comparative immunology have furthered our understanding of the origins and function of the adaptive immune system.