BLD 434 Topics 16–20: Parasite Immunity, Mucosal Immunity, Immunological Memory, Vaccines, and Unconventional Lymphocytes

Vocabulary practice flashcards covering parasite immunity and granulocyte function, mucosal immunology and GALT architecture, immunological memory, vaccination strategies, and unconventional lymphoid populations.

$$Fc\epsilon RI$$

A high-affinity receptor for IgE expressed on resting mast cells, basophils, and activated eosinophils that triggers degranulation upon antigen cross-linking.

Basophils

Granulocytes recruited at the onset of a Th2 response that secrete large amounts of IL-4 and IL-13, express CD40L to bind CD40 on B cells, and release histamine to impair tick attachment and feeding in anti-tick immunity.

Hypereosinophilia

An abnormally high level of eosinophils in the blood or tissues, resulting in a toxic response capable of damaging both invading parasites and host tissues.

Major Basic Protein (MBP)

A preformed toxic protein stored in eosinophil granules that directly kills multicellular parasites and induces histamine release from mast cells.

Eosinophil Peroxidase

A preformed granule enzyme of eosinophils that kills parasites by catalyzing halogenation and stimulates mast cells to release histamine.

Eosinophil-Derived Neurotoxin (EDN)

A preformed cytotoxic granule component of eosinophils that kills parasites through neurotoxic activity and exerts antiviral effects by degrading RNA.

Mast Cells

Granulocytes present in nearly all vascularized tissues that express $Fc\epsilon RI$, TLRs, and Fc receptors for IgG and IgA, becoming saturated with polyspecific IgE molecules that retain antigen-binding specificities from primary parasite exposures.

Gut-Associated Lymphoid Tissues (GALT)

A collection of organized secondary lymphoid tissues and isolated lymphoid follicles located in the gut wall that drain into mesenteric lymph nodes, the most abundant lymph nodes in the body.

Lamina Propria

The mucosal tissue layer situated beneath the epithelium that functions as the effector compartment housing activated immune cells.

M Cells (Microfold Cells)

Specialized cells within the follicle-associated epithelium positioned over Peyer's patches and lymphoid follicles that transport microorganisms and antigens from the gut lumen into secondary lymphoid tissue.

Oral Tolerance

The active suppression of immune responses against dietary antigens, mediated by dendritic cells in mesenteric lymph nodes presenting antigens to $CD4^+CD25^+\text{FoxP3}^+$ regulatory T ($T_{\text{reg}}$) cells in the presence of IL-10.

Mucosal Immunity

A defense system characterized by the normal presence of pre-activated immune cells and the deliberate blockage of inflammatory responses, allowing infections to be eliminated with minimal tissue damage.

Intraepithelial Lymphocytes (IELs)

Distinct $CD8^+$ T cells situated directly within the mucosal epithelial layer that remain perpetually active due to persistent stimulation from gut contents.

Poly-Ig Receptor

A specialized receptor on mucosal epithelial cells that transports dimeric (secretory) IgA across the epithelium to expel pathogens from the lamina propria.

Neonatal Fc Receptor (FcRn)

A transport protein that carries IgG antibodies from the bloodstream into mucosal secretions.

Long-Lived Plasma Cells

Small clones of plasma cells formed after pathogen clearance that reside in the bone marrow, continuously secreting antibody for months, years, or decades to sustain steady-state levels.

$$Fc\gamma RIIB1$$

An inhibitory Fc receptor expressed on naive B cells that binds the Fc region of pathogen-bound IgG, delivering a negative signal that induces naive B cell apoptosis.

Hemolytic Disease of the Fetus and Newborn (HDFN)

A severe hemolytic condition occurring in second or subsequent pregnancies of an RhD-negative mother carrying an RhD-positive fetus, caused by maternal high-affinity anti-RhD IgG crossing the placenta and destroying fetal erythrocytes.

RhoGAM (Rho(D) Immune Globulin)

An exogenous preparation of anti-RhD IgG infused into RhD-negative mothers to coat fetal erythrocytes and cross-link $Fc\gamma RIIB1$ on maternal naive B cells, preventing primary RhD sensitization.

Original Antigenic Sin

The immunological tendency of memory responses to rely exclusively on antibodies against epitopes shared with the original viral strain, because pre-existing IgG inhibits naive B cells specific for novel epitopes via $Fc\gamma RIIB1$.

Herd Immunity

A public health phenomenon where a high proportion of a population possesses immunity ($>85\%$ generally, $>95\%$ for measles), making epidemics unlikely because pathogens fail to find susceptible hosts.

Smallpox Eradication Factors

The specific biological traits that enabled global eradication of smallpox: the virus evolves slowly with conserved antigenic epitopes, natural infection and vaccination occur in the skin, and it only infects humans.

Killed (Inactivated) Vaccine

A vaccine composed of whole virions or bacteria whose nucleic acids have been completely and reliably inactivated, preventing replication while retaining immunogenicity (e.g., Rabies, Salk polio).

Live-Attenuated Vaccine

A vaccine containing a mutant form of live virus that grows poorly in human cells and is non-pathogenic, eliciting robust B-cell and T-cell responses by mimicking natural infection (e.g., MMR, Sabin polio).

Circulating Vaccine-Derived Poliovirus (cVDPV)

A virulent variant of poliovirus that evolves from the live-attenuated Sabin oral vaccine strain during prolonged circulation in under-immunized populations.

Recombinant Subunit Vaccine

A vaccine containing isolated, highly antigenic pathogen components produced using recombinant DNA technology, such as HBV surface antigen ($\text{HBVsAg}$) grown in baker's yeast.

Toxoid

A bacterial toxin that has been deliberately inactivated by chemical or heat treatment to eliminate toxicity while generating high-affinity neutralizing antibodies.

Conjugate Vaccine

A vaccine in which a target bacterial carbohydrate antigen is chemically linked to a carrier protein or toxoid to recruit helper T cells for carbohydrate-specific antibody production.

Adjuvant

A component included in subunit or conjugate vaccines to stimulate innate pattern recognition receptors (e.g., TLRs) and initiate the local inflammation necessary for adaptive immune activation.

Natural Killer (NK) Cells

Innate lymphoid cells defined by the surface phenotype $CD16^+CD56^+CD3^-$ that provide early cytotoxic responses and cytokine production (e.g., IFN-$\gamma$) governed by IL-12 or IL-15 prior to adaptive T-cell immunity.

Dendritic Cell–NK Cell Synapse

A regulatory interaction where abundant NK cells kill immature dendritic cells to limit inflammation, whereas scarce NK cells promote DC maturation and subsequent activation of adaptive immunity.

NK Cell Activating and Inhibitory Receptors

A diverse array of more than 30 receptor types (e.g., activating CD94:NKG2C, NKG2D, CD16; inhibitory CD94:NKG2A, KIRs) that NK cells integrate against MHC class I and other ligands to discern healthy from unhealthy self-cells.

Natural Killer T (NKT) Cells

Unconventional tissue-resident lymphoid cells expressing an $\alpha\beta$ TCR that recognize lipid and glycolipid antigens presented on CD1d, responding within 4 hours through cytokine secretion or cytotoxicity.

$\gamma\delta$ T Cells

Unconventional T cells that detect lipids via CD1 and do not undergo thymic negative selection, allowing them to recognize both self and non-self lipids to promote tissue repair through cytokine secretion.

B-1 Cells

Unconventional B lymphocytes primarily resident in tissues (rare in blood and lymph nodes) that produce substantial amounts of natural IgM antibodies without requiring helper T cells.

Marginal Zone B Cells

Unconventional B cells located in the blood and spleen that rapidly survey incoming antigens from blood and lymph to control infections until conventional lymphocytes arrive.

Innate Lymphoid Cells (ILCs)

Non-B, non-T tissue-resident lymphocytes derived from the common lymphoid progenitor, consisting of five distinct subtypes: ILC1, ILC2, ILC3, lymphoid tissue inducer (LTi) cells, and NK cells.