Physiology
Peter Sagar, Andrew G. Hill, Charles H. Knowles, Stefan Post, Willem A. Bemelman, Patricia L. Roberts, Susan Galandiuk, John R.T. Monson, Michael R.B. Keighley, Norman S. Williams in Keighley & Williams’ Surgery of the Anus, Rectum and Colon, 2019
The human gut harbours >100 trillion microbes – the gut microbiota. Most reside in the colon. Gut microbiota are essential for the development of gut mucosal immunity. Microbiota-driven immune response can prevent the development of inappropriate inflammation, which allows the microbiota to survive in the inflammatory free environment. Host-microbial symbiosis is essential for gut homeostasis. If a pathogen penetrates physical barriers, then the innate immune system provides immediate non-specific response mediated by T lymphocytes and the humoral immune system provides a slower, antigen specific response mediated by antibodies produced by B lymphocytes. The function of T cells and B cells is to recognise specific ‘non-self’ antigens, during a process known as antigen presentation. The cells generate specific responses that are tailored to eliminate specific pathogens or pathogen-infected cells. B cells respond to pathogens by producing large quantities of antibodies which neutralise foreign objects, i.e. bacteria and viruses. In response to pathogens, some T cells, called T helper cells, produce cytokines that direct the immune response, whilst other T cells, called cytotoxic T cells, produce toxic granules which induce the death of pathogen-infected cells. Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered in the form of memory cells.
The immune and lymphatic systems, infection and sepsis
Peate Ian, Dutton Helen in Acute Nursing Care, 2020
Lymphocytes are the cells of the lymphatic system. Produced in the bone marrow, they form part of the cell-mediated response to antigens. As their name suggests, they spend most of their life cycle, which is about 2–4 years, within the lymphoid tissues. There are different types and sizes of lymphocytes, T cells and B cells. T cells are produced in the bone marrow, but are matured (or become immunocompetent) within the thymus. B cells are also produced in the bone marrow, but remain there to mature and become immunocompetent (see Figure 12.2). The T and B cells are exposed to antigens, normally in the lymphoid tissue, where they differentiate and mature. Within the T and B cell population, there are a range of cells with differing functions. B cells mediate the humoral or antibody response and T cells mediate the cellular immune response.
Adaptive Tumor Suppression
John Melford in Pocket Guide to Cancer, 2017
B-cells perform several critical roles for the adaptive immune system that include the production of antibodies, presentation of antigens, and production of regulatory cytokines. They bind to soluble antigen molecules present in the extracellular fluid, or on the surface of antigen-presenting cells such as macrophages and dendritic cells. After binding, antigens are engulfed, broken down into fragments, attached to MHC Class II protein molecules, and presented on the outer cell membrane. The binding of an antigen to a B-cell activates it. Helper T-cells attach to such activated B-cells, and stimulate them to divide by secreting chemical messengers. Consequently, the number of B-cells doubles every six hours, so that after a week about 20,000 are generated each able to produce the same antibody. Many of these B-cells then quickly differentiate into plasma cells that are suited to ramp up production of their antibody, producing 2000 per second. This helps to make the immune response specific to an invading pathogen. As a given microorganism has any number of antigens, it’s very likely a single infection will trigger ramping up production of many different antibodies.
SPLICELECT™: an adaptable cell surface display technology based on alternative splicing allowing the qualitative and quantitative prediction of secreted product at a single-cell level
Published in mAbs, 2020
Christel Aebischer-Gumy, Pierre Moretti, Romain Ollier, Christelle Ries Fecourt, François Rousseau, Martin Bertschinger
Interestingly, the human immune system provides an additional and elegant way to link cell surface display and secretion. B cells are the antibody producers in the human immune system. Each B cell expresses a single antibody specifically binding a single antigen. In resting B cells (memory cells), the antibody is predominantly membrane-bound. Upon recognition of its antigen, a B cell will proliferate into plasma cells expressing a huge amount of secreted antibody.44 The only difference between the two antibody isoforms is a C-terminal extension of the membrane-bound version with a transmembrane region.45 The controlled transition between the two isoforms of antibody (membrane-bound and secreted) is achieved by alternative splicing.45,46 Splicing describes the precise excision of the introns of the mRNA, accomplished by a protein complex called spliceosome that is able to recognize consensus sequences: the 5ʹ splice donor (5ʹ SD) and 3ʹ splice acceptor (3’SA) sites at the intron/exon borders and the branch point and the poly pyrimidines (poly(Y)) tract in the intron. The efficiency of the splicing depends largely on the different consensus sequences, but also on so-called splicing enhancer and repressor sequences present in both introns and exons. Alternative splicing describes the mechanisms by which a single pre-mRNA is matured into different mRNA, a process that is usually highly regulated by interaction of many different factors.47–58
Immunobiology and nanotherapeutics of severe acute respiratory syndrome 2 (SARS-CoV-2): a current update
Published in Infectious Diseases, 2021
Ifeanyi Elibe Mba, Hyelnaya Cletus Sharndama, Goodness Ogechi Osondu-chuka, Onyekachi Philomena Okeke
We summarise by stating that cells infected with SARS-CoV-2 undergo pyroptosis and produce several molecules that induce epithelial and endothelial cells and also macrophages. The production of pro-inflammatory proteins (cytokines and chemokines) causes T cells, macrophages, and monocytes to migrate to the site of infection. The released IFNϒ from T cells triggers a loop of pro-inflammatory feedback. The successful immunological response involves (1) the T cell-mediated elimination of the infected cells (2) antibody-mediated inactivation of the SARS-CoV-2. These antibodies are produced by B cells. (3) Recognition of the infected cells by macrophages and subsequent phagocytosis. However, multiple organ damage (dysfunctional immunological response) can result from (1) excess immunological response due to excessive infiltration of cells of the immune system and (2) an increase in a cytokine storm (IL-6, IL-2, IP-10, IL-10, IFNϒ, GCC SF, TNF, MIP1α) due to the excessive infiltration. The production of the non-neutralising antibody by B cells can lead to the viral infection’s ADE (antibody-dependent enhancement). Although the information is rapidly emerging, the exact underlying mechanism of immunological reactions against SARS-CoV-2 remains elusive. The source of the several inflammatory reaction evidence during the reaction is unknown. More studies are urgently needed to understand the interplay between SARS-CoV-2 and the immune system comprehensively.
Immunogenicity and protection efficacy of enhanced fitness recombinant Salmonella Typhi monovalent and bivalent vaccine strains against acute toxoplasmosis
Published in Pathogens and Global Health, 2021
Fei-Kean Loh, Sheila Nathan, Sek-Chuen Chow, Chee-Mun Fang
B cells are the hallmark of humoral immunity for their ability to secrete specific antibodies that can neutralize the antigens. Among the antibody subtypes, IgG antibodies have been found to opsonise T. gondii for phagocytosis and inhibit parasite binding to the host cell receptors [54]. The low IgG titers detected in CVD910 vector control proved that S. Typhi live vector and recombinant T. gondii antigen booster has limited contribution in enhancing IgG production. Furthermore, low IgG titers were detected in the mouse group receiving monovalent CVD910-GRA2. Hence, the strong T. gondii-specific humoral immunity in CVD910-GS group is most likely contributed by the immunogenic B cell epitopes present in the SAG1 antigen. In complement, the mice immunized with peptide containing B-cell epitopes of SAG1 (amino acids 301–320) had shown to produce high titers of IgG [55,56].
Related Knowledge Centers
- Adaptive Immune System
- Antibody
- Antigen Presentation
- Humoral Immunity
- Memory B Cell
- White Blood Cell
- Lymphocyte
- Cytokine
- B-Cell Receptor
- Antigen-Presenting Cell