Immunology Terms Starting With E
Immunology Glossary: E
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Effector Cell
/ eh-FEK-tor sel / · Latin effector (one who accomplishes) + Latin cella
Effector Cell is a mature, activated immune cell that directly executes immune functions including antibody secretion, pathogen killing, or cytokine-mediated regulation, as distinguished from naive or memory precursor cells.
After activation by antigen and co-stimulatory signals, naive lymphocytes differentiate into effector cells with expanded functional capacity over three to five days. B cell effectors are antibody-secreting plasma cells; T cell effectors include cytotoxic CD8 T cells that kill infected targets and CD4 helper T cells that coordinate immune responses through cytokine production. Effector cells are typically short-lived, surviving days to weeks before undergoing apoptosis, while a small fraction differentiates into long-lived memory cells that persist after pathogen clearance.
Innate effector cells such as neutrophils and natural killer cells do not require prior sensitization and can begin executing their functions within minutes of activation.
During the peak of an acute viral infection, a single antigen-specific CD8 T cell can undergo up to 15 rounds of division in seven days, generating a clone of more than 10,000 daughter effector cells from one precursor, a magnitude of expansion first quantified in lymphocytic choriomeningitis virus studies in mice.
Immune System Fun Facts →Every immune cell is always an effector cell. Many immune cells exist as naive, resting, regulatory, or memory cells and only acquire effector function after receiving the appropriate activation signals.
During Listeria monocytogenes infection in mice (Mus musculus), neutrophils arrive at the site of bacterial replication within two to four hours and release antimicrobial granule contents that reduce bacterial burden by several orders of magnitude before T cells are activated. Each neutrophil survives only six to twelve hours at the inflammatory site before undergoing apoptosis.
Eosinophil
/ ee-oh-SIN-oh-fil / · Greek eos (dawn, rosy) + philein (to love)
Eosinophil is a granulocyte with large cytoplasmic granules that stain with the acidic dye eosin, mediating anti-parasite immunity and contributing to allergic and asthmatic inflammation through the release of cytotoxic granule proteins.
Eosinophils constitute two to four percent of circulating white blood cells and are recruited to parasitized tissues and allergic inflammatory sites by eotaxin chemokines and IL-5. Granules contain major basic protein, eosinophil cationic protein, and eosinophil peroxidase, which are toxic to helminth parasites but also damage host epithelium in allergic disease. Eosinophilia, an elevated blood eosinophil count above 500 cells per microliter, occurs in allergic disease, parasitic infection, and certain malignancies including Hodgkin lymphoma.
Beyond cytotoxicity, eosinophils secrete cytokines such as IL-4 and TGF-beta that shape tissue remodeling and regulate the local immune environment.
Eosinophils are among the longest-lived granulocytes: while neutrophils survive only six to twelve hours in circulation, eosinophils persist for eight to twelve days in the blood and can survive for weeks in tissues, particularly in the gastrointestinal tract, where they are present even in healthy individuals.
Eosinophils only fight parasitic infections. Eosinophils also drive allergic diseases such as asthma and eosinophilic esophagitis by releasing toxic granule proteins that damage airway and mucosal tissues in the complete absence of any parasite.
During infection with the roundworm Ascaris lumbricoides in humans, blood eosinophil counts can rise from a normal level of 100 to 400 cells per microliter to more than 5,000 cells per microliter during larval migration through the lungs. This eosinophilia peaks approximately two weeks after initial infection and coincides with the Loeffler syndrome pneumonitis caused by larval tissue damage.
Epitopes
/ EP-ih-tohps / · Greek epi (upon) + topos (place)
Epitopes are the specific molecular regions of an antigen that are directly recognized and bound by antibody variable regions or T cell receptors, representing the minimal structural unit required for immune recognition.
B cell epitopes are continuous or discontinuous surface structures on intact antigens recognized by antibody variable regions or membrane-bound B cell receptors; discontinuous epitopes depend on the three-dimensional folding of the antigen and are destroyed by denaturation. T cell epitopes are short linear peptide fragments of 8 to 25 amino acids bound within the groove of MHC molecules and recognized by T cell receptors, a process requiring prior antigen processing by antigen-presenting cells. A single antigen molecule typically contains multiple distinct epitopes recognized by different antibody clones, producing the polyclonal response characteristic of natural infection.
The influenza hemagglutinin protein, for example, carries both highly conserved epitopes near its stem region and rapidly mutating epitopes on its globular head, a distinction that drives current efforts to design universal influenza vaccines.
When Peter Jerne formulated the network theory of idiotypes in 1974, he proposed that antibodies themselves carry epitopes on their variable regions, called idiotopes, that can be recognized by other antibodies. This concept shaped early thinking about immune self-regulation and inspired experimental anti-idiotype vaccines.
Immune System Fun Facts →An epitope is the whole pathogen or entire antigen molecule. An epitope is only the specific small region, often just 5 to 15 amino acids or a comparable surface patch on a protein, that one antibody or T cell receptor contacts and binds.
Antibodies targeting the receptor-binding domain of SARS-CoV-2 spike protein recognize distinct epitopes on the same protein, and some of these epitopes overlap with the site the virus uses to attach to the ACE2 receptor. Neutralizing antibodies that bind epitopes within this 25-amino-acid receptor-binding motif block viral entry most effectively, while antibodies targeting other epitopes on the same protein may not neutralize infection at all.