Adaptive Immunity, Immunization, Serology, and Recombinant DNA Technology

Comprehensive practice flashcards covering Adaptive Immunity (Chapter 16), Immunization and Serology (Chapter 17), and Recombinant DNA Technology (Chapter 8).

What immunological event takes place within the germinal center of a lymph node?

The propagation of memory B cells, plasma cells, and antibodies.

Who discovered dendritic cells in 1973 and received the Nobel Prize for this discovery in 2011?

Ralph Steinman.

What are the four components of the multifaceted defensive strategy of the adaptive immune response?

1. Specificity (antigenic determinants), 2. Tolerance of "Self", 3. Minimal "Self" Damage, and 4. Immunological Memory.

Why are proteins the most potent antigens compared to carbohydrates, nucleic acids, and lipids?

Proteins are chemically stable and diverse due to their amino acid composition, whereas carbohydrates break down too quickly and nucleic acids and lipids possess unstable regions.

Approximately how many distinct epitopes can be recognized by the human adaptive immune system?

Approximately $10^{16}$ (100 trillion) different epitopes.

Which specific T cells downregulate self-reactive T cells in the thymus to preserve tolerance of self?

Regulatory T ($\text{T}_{\text{R}}$) cells.

What is a hapten, and what examples are cited that cause an immune response only when bound to a carrier protein?

A small non-immunogenic molecule that provokes an immune response only when linked to a larger carrier molecule (such as human serum albumin); examples include penicillin and urushiol (the toxin in poison ivy).

What uncontrolled immune event caused widespread pulmonary tissue destruction during the 1918 Spanish flu and COVID-19 pandemics?

A cytokine storm, which creates a positive feedback loop causing excessive accumulation of immune cells in lung tissue.

Approximately how many identical antibody-like receptors are displayed on the surface of a single naive B cell?

Approximately $100{,}000$ identical receptors.

Which cytokine released by $\text{T}_{\text{H}}2$ cells stimulates naive B cells to divide and form a clone?

Interleukin-4 ($\text{IL-4}$).

What fragments are generated when an Immunoglobulin G (IgG) molecule is cleaved at its hinge region by the enzyme papain?

Cleavage by papain yields two identical Fab (antigen-binding) fragments and one Fc (crystallizable) fragment.

Which immunoglobulin class comprises approximately $80\%$ of serum antibodies, crosses the placenta, and predominates in the secondary antibody response?

Immunoglobulin G ($\text{IgG}$), which has a serum half-life of $7\text{--}24\text{ days}$.

What are the structural monomer count, serum concentration, and primary role of Immunoglobulin M (IgM)?

It is a pentamer (5 monomers), accounts for $5\text{--}8\%$ of serum antibody with a half-life of $5\text{--}10\text{ days}$, activates complement, neutralizes toxins, and is the first antibody formed in a primary antibody response.

Where is Immunoglobulin A (IgA) found in the body, and in what structural forms does it occur?

It occurs as a monomer in serum ($10\text{--}15\%$ of serum antibodies; half-life $4\text{--}7\text{ days}$) and as a dimer secreted onto mucosal surfaces, tears, saliva, and colostrum.

What specific functions are carried out by Immunoglobulin E (IgE) and Immunoglobulin D (IgD)?

$\text{IgE}$ ($0.004\%$ of serum) binds mast cells and basophils to mediate allergic reactions and fight parasitic worms; $\text{IgD}$ ($0.2\%$ of serum) functions as a cell surface receptor on B cells to initiate the humoral response.

How do the primary and secondary antibody responses differ in peak timing and predominant immunoglobulin production?

The primary response takes $10\text{--}14\text{ days}$ to reach full titer and begins with $\text{IgM}$, whereas the secondary response takes only $4\text{--}7\text{ days}$ and produces a much higher, sustained titer of $\text{IgG}$.

What six mechanisms do antibodies employ to mediate antigen disposal without directly killing pathogens?

Viral inhibition, neutralization, opsonization, agglutination, precipitation, and phagocytosis enhancement (including complement-mediated lysis).

How does the Membrane Attack Complex (MAC) cause the destruction of a target pathogen?

Activated complement proteins assemble sequentially onto the pathogen membrane to form pores, causing loss of membrane integrity and cell lysis.

Which cells display MHC Class I versus MHC Class II, and which T-cell coreceptors recognize them?

MHC Class I is present on all nucleated cells (recognized by CD8 on cytotoxic T cells / CTLs); MHC Class II is present on professional antigen-presenting cells (macrophages, dendritic cells, B cells) and is recognized by CD4 on helper T ($\text{T}_{\text{H}}$) cells.

By what mechanism do activated cytotoxic T lymphocytes (CTLs) kill infected host target cells?

They recognize foreign antigen presented on MHC Class I and release perforins (which form pores in the target membrane) and granzymes (which induce apoptotic death).

Why does HIV infection cause severe immune deficiency affecting both cell-mediated and humoral responses?

HIV infects CD4-bearing cells ($\text{T}_{\text{H}}$, $\text{T}_{\text{R}}$, macrophages, dendritic cells, monocytes), leading to helper T cell depletion; without $\text{T}_{\text{H}}$ cells, neither B cells nor cytotoxic T cells can be fully activated.

What is serology, and what components make up blood serum?

Serology is the study of laboratory epitope-antibody reactions; serum is the fluid portion of blood consisting of water, minerals, salts, proteins, and antibodies, devoid of clotting agents.

What is the difference between active immunity and passive immunity?

Active immunity occurs when the host's own immune system responds to antigens by producing antibodies, T lymphocytes, and memory cells; passive immunity occurs when the host receives preformed antibodies from an outside source without developing memory.

What are the major advantages and drawbacks of artificially acquired passive immunotherapy?

It provides immediate prophylactic or therapeutic protection, but provides only temporary immunity ($1\text{--}3\text{ months}$), creates no memory cells, and risks serum sickness due to foreign serum proteins.

What clinical manifestations characterize serum sickness following foreign antiserum administration?

The recipient mounts an immune reaction against foreign proteins (such as complement or hormones), resulting in rashes at the injection site and swollen joints.

How do live attenuated vaccines differ from inactivated vaccines and toxoid vaccines?

Attenuated vaccines contain weakened microbes that multiply at low levels to elicit a strong response (requiring refrigeration); inactivated vaccines contain killed pathogens that induce a weaker response requiring booster shots; toxoids contain formaldehyde-inactivated bacterial exotoxins combined with adjuvants.

How are conjugate vaccines constructed, and what is their clinical purpose?

They attach poorly immunogenic bacterial capsular polysaccharides to a strongly immunogenic protein carrier (forming a hapten-carrier complex) to stimulate a protective immune response, such as in the Haemophilus influenzae type b (Hib) vaccine.

How do messenger RNA (mRNA) vaccines stimulate protective immunity?

Synthetic mRNA encoding a viral antigen (e.g., spike protein) is packaged into lipid nanoparticles; host cells take up the nanoparticles, translate the mRNA, and display the viral protein on their surface to stimulate antibody and T-cell production.

What is the function of the Vaccine Adverse Event Reporting System (VAERS)?

It is a national early warning system co-managed by the CDC and FDA that allows healthcare providers and the public to report adverse events following vaccination.

What is herd immunity, and what is the federal measles vaccination target for U.S. kindergartners?

Herd immunity occurs when a large percentage of a population is vaccinated, preventing outbreaks and protecting non-immunized individuals; the federal target for U.S. kindergartners is $95\%$.

How is antibody titer defined in a serological dilution test, and what does a rising titer signify?

Titer is the highest dilution (most dilute concentration) of serum that produces a visible antigen-antibody reaction; an increasing titer indicates active disease where the body is actively mounting an immune response.

How does a neutralization test determine whether a suspected lethal toxin is present in a sample?

The sample is mixed with a specific antitoxin and injected into a laboratory animal; if the animal survives, the antitoxin neutralized the toxin, confirming the toxin's identity, whereas failure to neutralize results in death.

What is the principle of a passive agglutination test?

Soluble antigens or antibodies are adsorbed onto artificial surfaces such as latex beads; when the matching antibody or antigen is introduced, visible clumping (agglutination) occurs at much lower concentrations.

Why does the lack of sheep red blood cell lysis indicate a positive result in a Complement Fixation Test?

If patient antibodies are present, they bind the added antigen and consume all available guinea pig complement; when the sheep RBC indicator system is added, no free complement remains to cause lysis.

What are the sequential steps in performing an Indirect Immunofluorescence Antibody (IFA) test for syphilis?

1. Syphilis spirochetes are fixed to a slide; 2. Patient serum is added (antibodies adhere if present); 3. Fluorescein-labeled antihuman antiglobulin antibodies ($\text{Ab}^*$) are applied; 4. Spirochetes fluoresce under UV illumination if patient antibodies were present.

How are monoclonal antibodies manufactured using hybridoma technology?

Antibody-producing plasma cells from an immunized mouse are fused with immortal myeloma cells to form hybridomas, which are cultured to yield identical antibodies specific to a single epitope.

What are four natural and artificial methods used to introduce recombinant DNA into bacterial cells?

Natural methods include transformation, transduction, and conjugation; the principal artificial laboratory method is electroporation.

What bacterial organism produces the restriction enzyme EcoRI, and what is its palindromic recognition sequence?

Escherichia coli RY13 produces EcoRI, which cleaves at the sequence $5'\text{-G}\downarrow\text{AATTC-3'}$.

Why are bacteria inoculated onto antibiotic-containing media following the insertion of a recombinant plasmid carrying the human growth hormone (HGH) gene?

The plasmid contains an antibiotic-resistance gene; plating on antibiotic media selects for transformed bacteria because only cells that took up the plasmid can survive.

What are the four essential reaction components required for Polymerase Chain Reaction (PCR)?

Target DNA template, DNA primers, deoxyribonucleotide triphosphates (dATP, dCTP, dGTP, dTTP), and heat-stable DNA polymerase (Taq polymerase).

What are the three temperature stages in a standard thermocycler PCR cycle, and what occurs during each?

1. Denaturation ($94^\circ\text{C}\text{--}95^\circ\text{C}$) to separate template strands; 2. Priming/Annealing ($48^\circ\text{C}\text{--}72^\circ\text{C}$, or cool to $60^\circ\text{C}\text{--}65^\circ\text{C}$) to allow primers to bind; 3. Extension ($68^\circ\text{C}\text{--}72^\circ\text{C}$) to allow DNA polymerase to synthesize the complementary strand.

What physical properties determine how DNA fragments separate during agarose gel electrophoresis?

DNA fragments are negatively charged and migrate toward the positive electrode; they are separated based on size and shape, with smaller fragments traveling farther through the agarose matrix.

Why do dideoxynucleotide triphosphates (ddNTPs) cause chain termination in the Sanger DNA sequencing method?

ddNTPs lack a $3'\text{ hydroxyl (–OH)}$ group, preventing DNA polymerase from forming a phosphodiester bond to add the next incoming nucleotide.

How does the bacterial CRISPR-Cas system function as an adaptive defense against bacteriophages?

Cas proteins capture pieces of invading viral DNA and insert them into the CRISPR array as spacers; upon subsequent infection, transcribed crRNAs guide Cas nucleases to cleave and inactivate matching foreign viral DNA.

Antigen

Any foreign substance or cellular component that provokes an immune response by stimulating B cells or cytotoxic T cells ($\text{T}_\text{C}$).

Epitope

The specific three-dimensional surface domain or antigenic determinant on an antigen directly recognized by antibodies or T-cell receptors.

Clonal Selection

The process by which an epitope specifically binds and activates a matching naive lymphocyte, stimulating it to proliferate into clones of identical effector and memory cells.

Somatic Recombination

The random mixing and rearrangement of variable, diversity, and joining gene segments in developing lymphocytes that creates the vast diversity of antigen receptors.

Perforin

A pore-forming cytolytic protein secreted by cytotoxic T lymphocytes ($\text{CTLs}$) that embeds in and punctures the plasma membrane of an infected target cell.

Granzyme

A cytotoxic serine protease released by cytotoxic T cells that traverses membrane pores formed by perforin to initiate apoptotic programmed cell death.

Major Histocompatibility Complex (MHC)

A group of polymorphic cell-surface glycoproteins (also termed human leukocyte antigens or HLA) that display self and nonself peptide antigens to T lymphocytes.

Naturally Acquired Active Immunity

Long-lasting protection resulting from natural infection with a microbe, during which the individual's immune system synthesizes specific antibodies and memory lymphocytes.

Naturally Acquired Passive Immunity

Short-term protection conferred when preformed maternal antibodies pass to an offspring across the placenta ($\text{IgG}$) or via colostrum and breast milk ($\text{IgA}$).

Artificially Acquired Active Immunity

Protective immunity and memory formation induced deliberately through vaccination containing treated or altered pathogens, toxins, or microbial antigens.

Subunit Vaccine

An immunization strategy containing only specific, isolated antigenic fragments or epitopes rather than intact whole microbes.

Toxoid

A purified bacterial exotoxin treated with chemical agents such as formaldehyde to destroy toxicity while retaining antigenicity for vaccination.

Monoclonal Antibodies

Identical antibodies produced in vitro by a single clone of hybridoma cells, all recognizing the exact same individual epitope.

Polyclonal Antibodies

A heterogeneous mixture of antibodies harvested from serum, produced by diverse B-cell lineages that recognize multiple distinct epitopes on an antigen.

Serological Reaction

An in vitro diagnostic laboratory test based on the specific molecular binding between an antigen or epitope and its corresponding antibody in blood serum.

Hemagglutination

The visible clumping of red blood cells caused by specific agglutinating antibodies binding to erythrocyte surface antigens, commonly used in blood typing.

Enzyme-Linked Immunosorbent Assay (ELISA)

A labeled antibody assay that uses an enzyme-substrate system to produce a measurable color change, detecting antibodies or antigens in fluid samples.

Immunochromatography

A rapid diagnostic method where fluid moves across a nitrocellulose strip, forming visible colored lines when target antigen-antibody complexes bind immobilized capture antibodies.

Cloning Vector

A self-replicating DNA molecule, such as a plasmid or bacteriophage, used in recombinant DNA technology to carry target genetic fragments into a host cell.

Restriction Endonuclease

A bacterial enzyme that cuts double-stranded DNA at precise, symmetric palindromic nucleotide sequences.

DNA Ligase

An enzyme that seals breaks in the sugar-phosphate backbone of DNA by catalyzing covalent phosphodiester bond formation between adjacent nucleotides.

Electroporation

A laboratory method utilizing high-voltage electrical pulses to temporarily generate microscopic pores in cell membranes, permitting entry of recombinant DNA.

Taq Polymerase

A heat-resistant DNA polymerase originally isolated from Thermus aquaticus that remains stable through repeated high-temperature ($94^\circ\text{C}\text{--}95^\circ\text{C}$) PCR denaturation cycles.

Dideoxynucleotide Triphosphate (ddNTP)

A modified chain-terminating nucleotide lacking both $2'$ and $3'$ hydroxyl groups ($\text{--OH}$), halting DNA polymerase extension in Sanger sequencing.

In an antibody titration assay, what does a declining antibody titer ratio ($\downarrow \text{Ab}:\text{Ag}$) indicate about a patient's clinical infection status?

A declining titer indicates disease regression or recovery, signifying that the active immune response is subsiding as the pathogen is cleared.

Why is patient serum heated prior to performing a Complement Fixation Test?

Heating inactivates the patient's native, endogenous complement proteins, ensuring that only a standardized amount of added exogenous complement (such as guinea pig complement) is present in the assay.

What constitutes a negative result in a Complement Fixation Test, and why does this reaction occur?

Hemolysis (lysis) of indicator sheep red blood cells; it occurs because patient antibodies were absent, leaving the added complement free to bind and lyse antibody-sensitized sheep erythrocytes.

What is the primary technical advantage of adsorbing soluble antigens or antibodies onto latex beads in a passive agglutination assay?

It converts soluble reactants into particulate carriers, dramatically increasing sensitivity and allowing visible clumping (agglutination) to be observed at much lower concentrations.

In an indirect ELISA, what is the specific role of the secondary antibody?

It is an enzyme-conjugated anti-human antibody that binds specifically to the patient's primary antibodies attached to the well, subsequently converting an added substrate into a detectable colored product.

Why does a positive ELISA test detecting anti-HIV antibodies indicate active viral infection rather than mere past exposure?

HIV causes a persistent, chronic lifelong infection that the immune system cannot clear; therefore, the presence of specific antibodies directly correlates with active infection.

In lateral flow immunochromatography (rapid antigen tests), what mechanism creates the visible colored test band?

Target antigen bound to mobile colloidal metal-labeled antibodies becomes captured and concentrated by immobilized anti-antibodies along the fixed detection strip.

In an ABO blood typing hemagglutination assay, what causes clumping when anti-A agglutinin antibodies are mixed with patient red blood cells?

Specific binding and cross-linking between the bivalent anti-A antibodies and corresponding Type A surface carbohydrate antigens on the patient's erythrocytes.

In serological diagnostic testing, what is the fundamental difference between using a known antibody versus a known antigen?

A known antibody is used to identify an unknown pathogen or antigen in a patient specimen, whereas a known antigen is used to detect specific antibodies in patient serum to evaluate exposure or immunity.

In an Indirect Immunofluorescence Antibody (IFA) test, to which component does the fluorescein-labeled secondary antiglobulin ($\text{Ab}^*$) bind?

It binds specifically to the constant ($\text{Fc}$) region of human antibodies that have adhered to the antigen fixed on the slide.