[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$frW1yjPMihVl6D0cia4XMVKb80im5WzNwcz3GTHBg52I":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":47},[4,8,12,16,20,24,28],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":46},"superantigen-examples-roles","Superantigen (SAg): Examples and Roles",null,"Acharya Tankeshwar","2019-03-20","2025-12-29",false,"immunology","Superantigens are microbial peptides that can polyclonally activate a large fraction of T cells (up to 20%). They escape normal antigen processing by antigen presenting cells (APCs) and can directly bind to T cell receptor (TCR).\n\nThis binding of TCR with MHC-II by superantigen results in polyclonal activation of T cells, ultimately resulting in life-threatening autoimmune responses, even deaths.\n\n![ - Superantigen interaction with TCR-MHC-II(Source)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FSuperantigen-1.jpg)Figure: Superantigen interaction with TCR-MHC-II(Source)\n\nSuperantigens bind simultaneously to the **Vβ** domain of a T-cell receptor and the α chain of a class II MHC molecule. Cross linkage of a T-cell receptor and class II MHC molecule produces an activating signal that induces T-cell activation and proliferation. The number of T cells sharing Vβ domain is high as a consequence, superantigen activates many T Cells with different specificity.\n\nSuperantigens polyclonally activate a large fraction (up to 25%) of the T cells, producing a massive immune response. In contrast, in T-dependent antigen, only a fraction of (1 in 10^6 -10^4) of the T cell population can recognize the antigen and become activated. The massive activation of T cells results in overproduction of TH cell cytokines (TNF alpha, IL-1, IL-6), leading to systemic toxicity, multi-organ failure, and even death.\n\nBoth exogenous and endogenous superantigens have been identified. Exogenous superantigens are soluble proteins secreted by bacteria e.g. *Staphylococcus aureus* (TSST-1) and [*Streptococcus pyogenes*](\u002Fstreptococcus-pyogens-gas-common-characteristics-virulence-factors-diseases-key-tests\u002F) (exotoxin A and B) . Endogenous superantigens are cell-membrane proteins are encoded by certain viruses that infect mammalian cells e.g. mouse mammary tumour virus (MMTV) and Epstein-Barr virus (EBV) that infect mammalian cells.\n\n### Examples of Bacterial Superantigens and their roles\n\n1. Staphylococcal enterotoxins: Food poisoning\n2. Staphylococcal toxic shock toxin (TSST-1): Toxic shock syndrome\n3. Staphylococcal exfoliating toxins: Scalded skin syndrome\n4. Streptococcal pyrogenic exotoxins (exotoxin A and exotoxin B): Shock\n\n### Conventional antigen Vs. Superantigen\n\nSome of  the key features of [conventional antigen](\u002Fantigen-structure-types-factors-affecting-immunogenicity\u002F) and superantigen is summarized in the table below:\n\n![](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FSuper-Antigen.png)\n\nDifference between conventional antigen and superantigen\n\n| Properties | Conventional Antigen | Superantigen |\n| --- | --- | --- |\n| Nature | Antigens are foreign substances (primarily proteins and polysaccharide) or altered self-proteins that induces a specific immune response. | Superantigens are microbial peptides that can polyclonally activate a large portion of T cells. |\n| Antigen Processing and Presentation | Conventional protein antigens are processed by B cell and a peptide of the protein antigen is presented to its matching antigen-specific CD4 T cell via MHC-II-peptide :TCR | Superantigens are not processed intracellularly, instead, they bind class II MHC molecules as intact macromolecules and bind outside of the peptide-antigen binding groove. |\n| Binding with T cells | Classical antigens bind to the highly variable peptide groove of the T-cell receptor. | Superantigen binds\u002Finteract with the more conserved Vβ region of T cell receptor. All T cells that express that particular Vβ region are subject to activation regardless of antigen specificity. |\n| Need of costimulatory signal | Successful T cell activation by conventional antigen requires multiple signals. Presentation of MHC-II-peptide-TCR is not enough to stimulate T cells. It requires co-stimulatory signal provided by an interaction between members of the B7 family (either CD80 or CD86) on APCs and CD28 on T cells. | Superantigens can activate T lymphocytes in the absence of costimulatory molecules. |\n| T Cell Activation | Conventional peptide antigens generally activate only a small fraction of the T cell population (i.e., <0.01% of T Cells). | Superantigens (SAgs) can stimulate 2-30% of the T cell repertoire. |\n\n**References and further reading**\n\n- [Kuby Immunology, 8th Edition](https:\u002F\u002Famzn.to\u002F2YdCgvR)\n- [Superantigen: ScienceDirect](https:\u002F\u002Fwww.sciencedirect.com\u002Ftopics\u002Fpharmacology-toxicology-and-pharmaceutical-science\u002Fsuperantigen)",[],[],[],[48,54,61,66,70,74,79,84,88,92],{"slug":49,"name":38,"description":50,"image":51,"body":52,"postCount":53},"acharya-tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",433,{"slug":55,"name":56,"description":57,"image":58,"body":59,"postCount":60},"ashma-shrestha","Ashma Shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",81,{"slug":62,"name":63,"description":64,"image":37,"body":37,"postCount":65},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":67,"name":68,"description":64,"image":37,"body":37,"postCount":69},"samikshya-acharya","Samikshya Acharya",20,{"slug":71,"name":72,"description":64,"image":37,"body":37,"postCount":73},"alisha-tripathi","Alisha Tripathi",6,{"slug":75,"name":76,"description":77,"image":37,"body":37,"postCount":78},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":80,"name":81,"description":82,"image":37,"body":37,"postCount":83},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":85,"name":86,"description":64,"image":37,"body":37,"postCount":87},"srijana-khanal","Srijana Khanal",18,{"slug":89,"name":90,"description":82,"image":37,"body":37,"postCount":91},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":93,"name":94,"description":64,"image":37,"body":95,"postCount":96},"nisha-rijal","Nisha Rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]