Self & Other · A Glossary of Medical News
The Processes
Cytokine storm. A runaway inflammatory response in which cytokines amplify each other faster than the system can resolve them. Can occur in severe infection, in some autoimmune crises, and as a managed side effect of CAR-T therapy.
Complement. A set of about thirty proteins that float in the blood, bind to bacterial and other foreign surfaces, and either tag them for destruction or directly poke holes in them. One of the oldest parts of the immune system, evolutionarily speaking.
MHC / HLA. The molecular ID badges every cell wears, displaying samples of what is currently inside that cell. T cells read them constantly. The same molecules go by different names in different contexts: MHC (in textbooks and other animals) and HLA (in humans). MHC class I is on almost every cell. MHC class II is mostly on dendritic cells, macrophages, and B cells.
Histamine. The most famous chemical released by mast cells. Causes blood vessels to widen and leak, smooth muscle to contract, nerve endings to fire (itching). The thing antihistamines block.
Adjuvant. A substance added to a vaccine to make the immune response stronger. Without an adjuvant, many vaccines would produce only weak immunity. Common adjuvants include aluminum salts and certain lipids. The sore arm after a vaccine is mostly the adjuvant doing its job.
The Processes
Mechanisms and patterns the immune system runs on.
Inflammation. The general term for the local immune response to injury or infection: redness, swelling, heat, pain. Acute inflammation is brief and resolves. Chronic inflammation is sustained and can damage tissue over time.
Phagocytosis. The process by which cells like macrophages and neutrophils engulf and digest particles — bacteria, dead cells, debris. Greek for “cell eating.”
Apoptosis. Programmed cell death. A controlled, orderly self-destruction process by which cells fold themselves up and are quietly cleaned up by macrophages. Used both as a normal developmental process and as a tool of immune defense — killer T cells trigger apoptosis in their targets.
Tolerance. The state of not responding to a particular antigen even though it could be recognized. Central tolerance happens in the thymus, where dangerous T cells are deleted before they can leave. Peripheral tolerance is maintained by Tregs and other regulatory mechanisms throughout the body.
Immunosurveillance. The general process by which the immune system continuously scans the body for cells that have gone wrong — infected, mutated, or cancerous. The basis of cancer immunology.
Sensitization. The first encounter that primes the immune system to recognize a particular antigen. In allergy, sensitization is the first exposure that produces IgE against an allergen; subsequent exposures then trigger the allergic reaction.
Immunogenic. Capable of provoking an immune response. A vaccine is designed to be immunogenic. A transplanted organ is immunogenic in ways we wish it weren’t. Used as both a positive (“strongly immunogenic vaccine”) and a negative (“immunogenic to the recipient”).
The Treatments
Modern medicine relies heavily on terms describing specific kinds of immune-modifying therapies. These are the ones that show up most in news coverage.
Vaccine. A preparation that triggers immune memory against a specific pathogen without causing the disease itself. Modern vaccines come in several types: live attenuated (weakened), inactivated (killed), subunit (a piece of the pathogen), and mRNA (the recipe for one viral protein, made temporarily by your own cells).
Live attenuated vaccine. A vaccine made from a real, replicating pathogen that has been weakened so much it can’t cause significant disease. Usually produces strong, long-lasting immunity. Examples: MMR, chickenpox.
Inactivated vaccine. A vaccine made from killed pathogens. Safe but generally produces less durable immunity, often requiring boosters. Examples: most flu vaccines, polio (in the US), hepatitis A.
Subunit vaccine. A vaccine containing just a piece of the pathogen — typically one or a few proteins. Examples: hepatitis B, HPV, the protein-based COVID vaccines.
mRNA vaccine. A vaccine that delivers a strand of mRNA encoding a viral protein, which the body’s own cells then briefly produce. The mRNA degrades within hours. Examples: the Pfizer/BioNTech and Moderna COVID vaccines.
Biologic. A drug made of large biological molecules — typically antibodies or fragments of antibodies — designed to target a specific protein in the body. Most biologics for autoimmune disease block specific cytokines (TNF, IL-6, IL-17) or specific cells (B cells). The class that has, more than any other, transformed treatment of autoimmune disease in the last twenty-five years.
Checkpoint inhibitor. A class of cancer immunotherapy drugs that releases the brakes on T cells, allowing the immune system to attack cancer cells it had been ignoring. The major targets are CTLA-4 (ipilimumab) and PD-1/PD-L1 (pembrolizumab, nivolumab, atezolizumab, others). Subject of the 2018 Nobel Prize.
CAR-T cell therapy. A cancer treatment in which a patient’s own T cells are extracted, engineered to carry a chimeric antigen receptor (CAR) that recognizes a cancer-specific protein, expanded in number, and infused back. Especially effective in certain blood cancers; harder for solid tumors.
IVIG / SCIG. Intravenous (or subcutaneous) immunoglobulin. Pooled antibodies from healthy donors, used to treat people with antibody deficiencies (CVID and others). Also used in some autoimmune conditions for less well-understood reasons.
Immunosuppressant. A drug that broadly dampens immune activity. Used in autoimmune disease, organ transplantation, and some inflammatory conditions. Older immunosuppressants (steroids, methotrexate, azathioprine) are nonspecific. Newer ones (biologics, JAK inhibitors) target specific pathways.
Steroids. In immune contexts, this almost always means corticosteroids — prednisone, hydrocortisone, dexamethasone, and their relatives. Powerful, broadly immunosuppressive, often the first line for severe autoimmune flares. Long-term use has a wide range of side effects.