T Cell Immunology and Serologic Laboratory Techniques Flashcards

Comprehensive vocabulary flashcards covering T cell maturation, TCR structure, serologic laboratory techniques, agglutination and precipitation assays, autoimmune testing, and tumor markers based on the provided lecture transcript.

CD4+ T Cells

Helper T cells whose main role is to secrete cytokines required for all immune responses.

CD8+ T Cells

Cytotoxic T cells whose main role is to destroy infected host cells, such as virally infected cells.

T Cell Receptor (TCR) Variable Region Structure

The antigen-binding portion of the TCR; for the $\alpha$ chain it consists of V and J segments, while for the $\beta$ chain it consists of V, D, and J segments.

T Cell Subsets Lineage

Categorization of T cells based on surface molecules (CD4+ vs. CD8+) that determine their lineage and immune functions.

CD3 Complex

A group of cell surface molecules expressed along with the $\alpha/\beta$ heterodimer that interacts with intracellular signaling pathways during T cell activation.

T Cell Repertoire

The total population of T cell clones within an individual, reflecting diverse antigen specificities determined by the variable regions of alpha and beta TCR chains.

Thymocyte

A developing T cell located in the thymus undergoing differentiation, selection, and maturation.

Double Positive Thymocyte

A developing thymocyte in the thymic cortex that simultaneously expresses both CD4 and CD8 cell surface markers.

Immunosurveillance

The sentinel role of circulating T cells and immune cells in host defense to continuously detect and defend against foreign pathogens.

T Helper Precursor Cell (Thp)

A naive CD4+ T cell that has left the thymus and requires antigen recognition and costimulatory signals in secondary lymphoid tissues to differentiate into an active cytokine-secreting T cell.

T Cell Anergy

A state of functional unresponsiveness or dormancy induced when a CD4+ T cell interacts with its specific antigen-MHC complex in the absence of costimulatory signals (e.g., CD28-B7).

Interleukin-2 (IL-2)

A primary T cell growth factor secreted by activated CD4+ T cells that acts via autocrine and paracrine mechanisms on high-affinity IL-2 receptors to trigger clonal expansion.

Pre-Cytotoxic T Lymphocyte (pCTL)

A naive CD8+ T cell that leaves the thymus and must encounter antigen fragment-MHC class I complexes along with costimulatory signals and IL-2 to differentiate into a functional cytotoxic T lymphocyte.

Complement Inactivation

The process of heating serum or body fluids at $56\,^{\circ}\text{C}$ for $30\,\text{minutes}$ to destroy complement activity and prevent interference or false results in serologic testing.

Antibody Titer

The reciprocal of the highest dilution of patient serum in which the antibody is still detectable and yields a positive reaction with antigen.

Fourfold Rise in Titer

An increase in a patient's antibody titer of at least two doubling dilutions over several weeks (e.g., $1:8$ to $1:32$), indicating a current or active infection.

Precipitation vs Agglutination

Precipitation involves the visible aggregation of soluble antigens with soluble antibodies into an insoluble complex, whereas agglutination involves the clumping of particulate antigens (e.g., RBCs or carrier beads).

Latex Particle Agglutination

An assay where specific antibodies (or antigens) are bound to latex beads, creating visible cross-linked aggregates upon binding to their target antigen in a test specimen.

Human Chorionic Gonadotropin (hCG) $\beta$-Subunit

The unique carboxy-terminal subunit of hCG targeted in pregnancy tests using monoclonal antibodies to prevent cross-reactivity with LH, FSH, and TSH.

In Vitro Agglutination Inhibition (Pregnancy Test)

An assay where patient hCG neutralizes anti-hCG reagent, preventing agglutination of added hCG-coated latex particles; absence of agglutination indicates a positive pregnancy result.

Flocculation Test

A serologic interaction between soluble antigen and antibody that yields a precipitate of fine particles, visible macroscopically or microscopically in a confined space.

Reagin

An antibody-like protein directed against damaged tissue or lipid antigens, measured in non-treponemal syphilis tests like VDRL and RPR.

Complement Fixation Assay

A two-step test where antigen and antibody react in the presence of complement, followed by adding sheep RBC indicators; lack of hemolysis indicates a positive test.

Radial Immunodiffusion (RID)

A single immunodiffusion assay where antigen diffuses radially from circular wells into agar containing antibody, forming a precipitin ring proportional to antigen concentration.

Mancini Method

An end-point radial immunodiffusion method read at maximal ring size ($24\text{ to }48\,\text{hours}$), where the square of ring diameter ($d^2$) shows a linear relationship to antigen concentration.

Fahey Method

A kinetic radial immunodiffusion method read before maximal ring size ($6\text{ to }12\,\text{hours}$), showing a logarithmic relationship between ring diameter ($d$) and antigen concentration.

Ouchterlony Double Diffusion Patterns

Precipitation patterns formed by double diffusion in agar showing identity (continuous V-arc), non-identity (crossing lines), or partial identity (spur formation).

Immunoelectrophoresis (IEP)

A technique combining serum protein gel electrophoresis with immunodiffusion against antibody placed in a parallel trough to yield arc-shaped precipitation patterns.

Immunofixation

A highly sensitive method combining protein electrophoresis with immunoprecipitation using monospecific antisera layered over migration lanes to classify monoclonal gammopathies.

Rocket Immunoelectrophoresis

An electroimmunodiffusion technique where an electric field drives antigen rapidly through an antibody-containing gel, forming cone-shaped rockets whose heights reflect antigen concentrations.

Enzyme Multiplied Immunoassay Technique (EMIT)

A homogeneous immunoassay for small molecules where antibody binding to an enzyme-drug conjugate inhibits enzyme activity, allowing unbound drug in patient serum to generate color.

Nephelometry

A technique measuring light scattered by insoluble antigen-antibody complexes in suspension to quantify complement components or immunoglobulin concentrations.

C-Reactive Protein (CRP)

An acute-phase protein rapidly released into serum following inflammation or tissue damage, serving as a non-specific indicator to monitor inflammatory activity.

Fluorescent Treponemal Antibody Absorption Test (FTA-Abs)

An indirect immunofluorescence assay for syphilis that uses sorbent to remove non-specific antibodies before reacting serum with Nichol's strain of Treponema pallidum.

Rheumatoid Factor (RF)

An autoantibody (commonly IgM or IgG) directed against the Fc portion of IgG, found in high titers in patients with rheumatoid arthritis.

Anti-Cyclic Citrullinated Peptide (anti-CCP)

A highly specific confirmatory ELISA test for rheumatoid arthritis that allows early diagnosis and assessment of joint erosion risk.

Hepatitis B Serologic Profile

The clinical pattern of viral markers (HBsAg, HBeAg, anti-HBs, anti-HBc, anti-HBe) used to evaluate disease stage, infectivity, recovery, or vaccination status.

IgM Anti-HBc

The initial core antibody produced in Hepatitis B virus infection, serving as the most specific marker for acute HBV diagnosis and persisting through the window period.

HBeAg

A soluble protein component of the Hepatitis B viral core whose presence in serum connotes high viral replication and high infectivity.

Antinuclear Antibody (ANA) Patterns

Immunofluorescent nuclear staining patterns (homogeneous, peripheral, speckled, nucleolar) that correlate with specific autoantibodies and systemic autoimmune diseases.

Clinical Value of Neoplastic Tumor Markers

The diagnostic and therapeutic monitoring applications of specific tumor markers (CEA, AFP, CA 125, $\beta\text{-hCG}$, prostate acid phosphatase) in neoplastic diseases.

Non-neoplastic Causes of Elevated Tumor Markers

Non-cancerous clinical conditions (such as pregnancy, hepatitis, IBD, or pancreatitis) that can cause serum elevations in tumor marker levels.

Alpha-fetoprotein (AFP)

A glycoprotein normally synthesized by fetal liver cells and yolk sac, used as a tumor marker for hepatocellular carcinoma and nonseminomatous germ cell tumors.

CA 125

A surface glycoprotein tumor marker expressed on coelomic epithelium, primarily used for diagnosis and monitoring of ovarian carcinoma.

Carcinoembryonic Antigen (CEA)

An oncofetal cell-surface antigen elevated in colorectal and other carcinomas, used clinically to monitor tumor progress, therapeutic response, and recurrence.

CA 19-9

A Lewis blood group carbohydrate antigen utilized as a primary biomarker for pancreatic and colorectal carcinomas, showing greater specificity for pancreatic cancer than CEA.

HER2/neu

An oncogene-encoded protein overexpressed in 15–20% of invasive breast cancers; indicates tumor aggressiveness and serves as a predictive marker for response to trastuzumab therapy.