The work was supported by grants from the National Institutes of Health. When someone gets a vaccine or is exposed to a new infectious agent, cells that recognize the invader but had never have been called into action before — called naive cells — respond by dividing like crazy and developing infection-fighting functions.
This creates a large pool of so-called memory cells, named for their ability to remember the specific infectious agent and respond effectively to repeat threats later. Over time, the large pool shrinks to a small number of long-term memory cells, which are primed to provide late protection. But scientists have debated how these memory cells are maintained and ready to strike for so long after the initial exposure.
This study found that one way the pool is maintained for years after vaccination is through the development of several unique features. On the surface and through the actions of their genes, they look like cells that have never been exposed to an infection, but on their DNA the researchers found a fingerprint, called a methylation pattern, that identifies them as having been through battle as an infection-fighting cell, which are called effector cells.
The research could have far-reaching implications. The new findings also upend the common top-down view of the brain. Get highlights of the most important news delivered to your email inbox.
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In more distant parts of the body, T cells are exposed to only small amounts of the virus, and some of those cells become long-term memory T cells specific to that virus.
These maintain a low level of constant vigilance, in case the virus ever returns. Vaccination When developing vaccines, the goal is usually to generate a stable population of long-term memory T cells. This study suggests that the best way to do that is to give a small amount of antigen, and, for vaccines that require multiple injections, not to give them too frequently. He adds that the amount of antigen for inducing a long-term memory T cells likely varies depending on the route of immunization and the form of antigen, and so the dosage for each vaccine will have to be determined through experiments.
He says the findings will likely not impact flu-vaccine design because existing dosages have already been optimized over many decades. However, the findings should be applicable to vaccines now under development for other diseases, such as HIV, tuberculosis and dengue fever, says Chen. Massachusetts Institute of Technology. Search MIT. Search websites, locations, and people. Enter keywords to search for news articles: Submit. Browse By. Interestingly, the absence of spleen and tonsils does not affect secondary responses to tetanus, suggesting an organ independent maintenance and reactivation for human memory B cells Memory B cells that reside in lymphoid organs and recirculate after re-exposure to antigen are phenotypically the same and do not represent different stages of maturity.
Additionally, it has been demonstrated that the human spleen is a major reservoir of long-lived vaccinia-specific memory B cells The route by which an antigen enters the body systemic vs. Protein antigens usually trigger B cells receiving T-cell help while polysaccharide antigens induce CSR in the absence of T-cell help.
Polysaccharide B cell responses to vaccination in humans have been reviewed in Mitchell et al. Antibody responses to soluble protein antigens and membrane proteins primarily induce IgG1, but are accompanied with lower levels of the other subclasses. On the other hand, antibody responses to bacterial capsular polysaccharide antigens is almost only restricted to IgG2 IgG4 antibodies are often formed following repeated or long-term exposure to antigen in a non-infectious setting Homeostatic IgA responses employ a polyreactive repertoire to bind to a broad subset of microbiota species and tend to be of low affinity.
In contrast, mucosal pathogens and vaccines elicit high-affinity, T-cell dependent antibody responses , Mucosal IgA responses through a T-cell dependent reaction that place in mucosal lymphoid follicles, such as intestinal Peyers' patches and mesenteric lymph nodes together called MALT for Mucosa-Associated Lymphoid Tissues Human IgA subtypes show distinct anatomical expression patterns, with monomeric IgA1 dominating in the serum and dimeric IgA2 in the gut Very few studies in humans have compared the induction of IgA and IgG secreting cells following various routes of immunization.
An early study compared oral, intranasal and systemic influenza virus vaccines in healthy adults. Additionally, oral and intranasal administration of antigen-induced IgA influenza-specific antibodies in external secretions In addition, immunization of African green monkeys with a live-attenuated H5N1 influenza vaccine resulted in more serum IgG neutralizing antibodies than IgA However, serum IgA antibodies had a molecular composition IgA1 vs.
IgA2 and J chain level distinct from that of IgA antibodies secreted in the gut, suggesting the involvement of different plasma cell populations Finally, analysis of long-term transcriptional profile between blood IgG and IgA influenza-reactive plasmablasts as well as influenza-negative IgA plasmablasts did not reveal any specialization based on isotype.
These data suggest that IgG and IgA vaccine—positive plasmablasts are largely similar, whereas IgA vaccine—negative plasmablasts appear to be transcriptionally distinct from antigen-induced peripheral blood plasmablasts Significant efforts in the HIV field are focusing on the design of vaccines that would induce the generation of broadly neutralizing antibodies bNAbs. Understanding the immunology behind the development of antibody potency and breadth following immunization is crucial in this context, not only to the HIV community The success of most vaccines relies on the generation of antibodies to provide protection against subsequent infection.
As discussed earlier in this review, Tfh cells are critical for the production of high-affinity B cell clones in the GC and thus the generation of long term memory, i. The feasibility of assessing GCs and Tfh responses from human lymph nodes has been limited, as GC B cells do not circulate in the blood, and lymph nodes are rarely sampled Recently, fine needle aspirates of the draining lymph nodes were used to longitudinally sample GC B cells and GC Tfh cells in non-human primates.
The lymph node fine needle aspiration technique has proven effective in terms of how many cells were recovered from the biopsy as well as in not disrupting the ongoing GC. The authors found that neutralizing antibodies in non-human primates correlate with GC B cell magnitude and Tfh help quality They also found that GCs peak weeks after the initial immunization.
Proteins that are not of extreme stability can be degraded, exposing epitopes that would normally be hidden or non-existent on a more native protein conformation. Slow immunogen release could improve the availability of intact antigen and epitopes of interest for the duration of the GC response Germline-targeting strategies aim to activate B cell precursors with potential interest for bNAbs generation, so that they will enter the GC, be selected and affinity matured and will generate memory B cells.
A vaccination protocol based on B-cell lineage differs from classic protocols in the fact that they may prime with one immunogen and boost with another or with a sequence of several different immunogens — It has been recently demonstrated that only immunogens above a certain affinity and in multimeric form are capable of inducing GCs dominated by B cells from a bNAb precursor starting with low precursor frequency These B cells successfully competed in GCs, underwent somatic hypermutation and differentiated into memory B cells.
Overall this study demonstrates that germline-targeting immunogens can overcome affinity, avidity, and inter-clonal GC competition challenges with high-affinity multimeric designs. Plasmablasts have been extensively studied in humans, especially in the context of influenza vaccination and infection. Little is known about B cells that become activated but do not differentiate into plasmablasts. We demonstrated that the CD21 low population was comprised of recent GC graduates that were refractory to GC reentry and seemed to be predisposed to differentiation into long-lived plasma cells Although clonally related to memory B cells and plasmablasts, CD21 low B cells form distinct clades within phylogenetic trees based on the accumulation of variable gene mutations.
Additionally, it is of great interest to understand how different vaccine compositions will affect the generation of memory B cells and LLPCs. Seasonal influenza vaccines exist as live-attenuated influenza virus LAIV , which more closely resembles natural immunity after infection, or as inactivated vaccines. LAIV have been used mostly in children but do not induce strong systemic antibody responses in adults The same was true for two different avian pandemic LAIV vaccines H5N1, H7N9 , although these vaccines elicited a long-term immune memory that was revealed after administration of a matched inactivated vaccine — To understand how LAIV vaccines can prime such a memory response, a detailed analysis of B cell responses in systemic and local lymphoid tissues in a non-human primate model was performed Interestingly, the authors found that the LAIV vaccine induced robust GCs in the mediastinal lung-draining lymph node and that both HA-reactive plasmablasts and memory B cells were found in the mediastinal lymph nodes after immunization.
Finally, it is believed that adjuvants can modulate humoral responses and retain antigen at the site of injection. Most studies have been done with alum and it remains unknown how other adjuvants such as AS03 and MF59 act on GCs and antigen release In the context of influenza vaccines, adjuvanted vaccines administered in patients with impaired immune responses, such as infants and the elderly, were shown to be beneficial — The generation of memory B cells and long-lived plasma cells is crucial to the long-term effectiveness of vaccines.
Understanding how to induce these different populations and modulate their effects both in animal models and human is essential to the design of better vaccines. Thus, the design of new immunogens, how to release them, as well as the mechanisms of actions of various adjuvants are the future of vaccines protecting against challenging or emerging infectious diseases.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We thank Patrick C. Wilson and Christopher T.
Stamper for critical discussion. Duration of humoral immunity to common viral and vaccine antigens. N Engl J Med. Multiple layers of B cell memory with different effector functions.
Nat Immunol. Memory B and memory plasma cells. Immunol Rev. Different B cell populations mediate early and late memory during an endogenous immune response. Class-switched memory B cells remodel BCRs within secondary germinal centers. Fas is required for clonal selection in germinal centers and the subsequent establishment of the memory B cell repertoire.
Cutting edge: hierarchy of maturity of murine memory B cell subsets. J Immunol. CD80 and PD-L2 define functionally distinct memory B cell subsets that are independent of antibody isotype. Memory B cells without somatic hypermutation are generated from Bcl6-deficient B cells. T-independent type II immune responses generate memory B cells. J Exp Med. Distinct cellular pathways select germline-encoded and somatically mutated antibodies into immunological memory.
A germinal center-independent pathway generates unswitched memory B cells early in the primary response. Generation of memory B cells inside and outside germinal centers. Eur J Immunol. A temporal switch in the germinal center determines differential output of memory B and plasma cells.
The generation of antibody-secreting plasma cells. Nat Rev Immunol. Plasma cell ontogeny defined by quantitative changes in blimp-1 expression. Early appearance of germinal center-derived memory B cells and plasma cells in blood after primary immunization. Rapid cloning of high-affinity human monoclonal antibodies against influenza virus.
Elucidation of seventeen human peripheral blood B-cell subsets and quantification of the tetanus response using a density-based method for the automated identification of cell populations in multidimensional flow cytometry data. Cytometry B Clin Cytom. Rapid and massive virus-specific plasmablast responses during acute dengue virus infection in humans. J Virol.
Polysaccharide-specific B cell responses to vaccination in humans. Hum Vaccin Immunother. Tangye SG. Staying alive: regulation of plasma cell survival. Trends Immunol. Static and dynamic components synergize to form a stable survival niche for bone marrow plasma cells. Blood Adv. The bone marrow: the major source of serum immunoglobulins, but still a neglected site of antibody formation.
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