Primary Immune Deficiency Diseases and Antiphospholipid Syndrome

Comprehensive vocabulary flashcards covering the components of the immune system, primary immunodeficiency disorders, diagnostic tests, and Antiphospholipid Antibody Syndrome (APAS).

Innate Immunity

The rapid, nonspecific first-line defense of the immune system that acts within minutes to hours of pathogen exposure and relies on recognizing general patterns.

Adaptive Immunity

A specific, memory-forming immune response that develops over time, allowing for faster and stronger responses upon reexposure to a pathogen.

B Lymphocytes (B cells)

Cells responsible for humoral immunity that develop in the bone marrow and produce antibodies that neutralize pathogens and promote opsonization.

T Lymphocytes (T cells)

Cells that provide cell-mediated immunity through direct and indirect mechanisms, such as coordinating responses or killing infected cells.

CD4+ Helper T cells

A subset of T cells that coordinate immune responses through the use of cytokines and cellular activation.

CD8+ Cytotoxic T cells

A subset of T cells that directly kill infected or malignant cells.

Central Tolerance

The elimination of strongly self-reactive lymphocytes during their development in primary lymphoid organs like the Thymus and Bone marrow.

Peripheral Tolerance

Mechanisms that suppress mature self-reactive lymphocytes in the body, including the action of regulatory T cells and anergy.

Primary Immunodeficiency Disorders (PIDs)

A group of disorders caused by an underlying inherited defect where one or more components of the immune system are absent or dysfunctional.

X-linked Agammaglobulinemia (XLA)

A condition caused by a BTK gene defect that prevents normal B cell maturation, leading to very low immunoglobulins and absent B cells.

Common Variable Immunodeficiency (CVID)

A disorder characterized by impaired antibody production that may manifest later in childhood or adulthood with variable clinical patterns.

Selective IgA Deficiency

The most common Primary Immunodeficiency Disorder, which is often asymptomatic but can predispose individuals to respiratory and gastrointestinal infections.

DiGeorge Syndrome

A T-cell immunodeficiency caused by a $22q11$ deletion, resulting in thymic aplasia, defective T-cell development, and hypocalcemia.

Severe Combined Immunodeficiency (SCID)

A fatal condition resulting from the absence of both humoral and cellular immunity, often caused by heterogenous factors like $\gamma$-chain or ADA deficiency.

Wiskott-Aldrich Syndrome

A combined immunodeficiency characterized by the classic clinical triad of immunodeficiency, eczema, and thrombocytopenia.

Ataxia Telangiectasia

A combined immunodeficiency disorder involving neurodegeneration, telangiectasis, and a predisposition to malignancy.

Chronic Granulomatous Disease (CGD)

A phagocytic disorder caused by an NADPH oxidase defect, which leads to impaired respiratory burst and an inability to kill certain pathogens.

Leukocyte Adhesion Deficiency

A condition involving defective integrins that causes impaired neutrophil migration from the bloodstream to the sites of infection.

Complement Deficiencies

Disorders that disrupt the complement cascade, leading to a higher susceptibility to bacterial infections and autoimmune diseases like lupus.

CH50

A basic laboratory screening test used to evaluate classical complement pathway activity; low levels indicate deficiencies in components $C1$ through $C9$.

AH50

A laboratory screening test used to evaluate alternative complement pathway activity, specifically identifying Factor B, Factor D, or properdin deficiencies.

Dihydrorhodamine (DHR) Assay

An intermediate laboratory test using flow cytometry to evaluate neutrophil function; abnormal results are used to diagnose Chronic Granulomatous Disease.

Delayed-Type Hypersensitivity (DTH) Skin Testing

A test that measures the response to recall antigens like candida or mumps; an absent response indicates defective T-cell-mediated immunity.

Antiphospholipid Antibody Syndrome (APAS)

An autoimmune thrombotic disorder characterized by vascular thrombosis and specific pregnancy complications associated with persistently positive antiphospholipid antibodies.

Lupus Anticoagulant (LA)

A functional laboratory test that measures prolonged phospholipid-dependent clotting time in vitro; inside the body, it promotes clotting.

Anticardiolipin (aCL) Antibodies

Autoantibodies that target cardiolipin, a fat molecule in cell walls; high levels of the IgG isotype carry a stronger risk for blood clots.

Anti-Beta-2-Glycoprotein I Antibodies

Antibodies directed against the plasma protein beta-2-glycoprotein I, which works closely with the clotting system.

Vascular Thrombosis

A clinical criterion for APS involving one or more clinical episodes of arterial, venous, or small-vessel thrombosis in any tissue or organ.

Pregnancy Morbidity (APS)

A clinical criterion for APS including fetal death at $\ge 10\text{th wk}$, premature birth at $\le 34\text{th wk}$ due to placental issues, or $\ge 3$ consecutive abortions before $10\text{th wk}$.

Aspirin (Mechanism in APAS)

Treats APAS by inhibiting thromboxane $A_2$ to improve blood flow and stimulating $IL-3$ for implantation and placental growth.

Heparin (Non-anticoagulant Action)

Protects the placenta in APAS by suppressing natural killer cell cytotoxicity and preventing complement activation and trophoblast inflammation.

Intravenous Immunoglobulin G (IVIg)

An advanced treatment that expands regulatory T cells, lowers $IL-12$, and enhances opsonization to achieve anti-inflammatory effects.

Think Zebra Mnemonic

A clinical reminder to consider Primary Immunodeficiency in patients with persistent, severe, or unusual infections, rather than assuming common conditions.

Dendritic Cells

Cellular components that bridge the innate and adaptive immune systems by engulfing pathogens and presenting antigens to other immune cells.

BTK Gene

A gene that, when defective, prevents normal B cell maturation and is the primary cause of X-linked agammaglobulinemia in approximately 85\text{%} of cases.