Introductory Microbiology: Innate Immunity, Adaptive Immunity, and Vaccination

Comprehensive practice flashcards for Introductory Microbiology (MMI 1053) covering Lecture 15 (Innate Immunity), Lecture 16 (Adaptive Immunity), and Lecture 17 (Vaccination, Immunoassays, and Immune Disorders).

What are the three main lines of host defense against disease?

The first line consists of nonspecific physical and chemical barriers; the second line consists of innate cellular responses, inflammation, fever, and antimicrobial substances; the third line consists of adaptive cellular responses including specialized lymphocytes (T cells and B cells) and antibodies.

How does innate immunity differ fundamentally from adaptive immunity?

Innate immunity refers to nonspecific, immediate defenses against any pathogen that do not confer immunological memory, whereas adaptive immunity is a highly specific response to a particular antigen that confers immunological memory for a faster response upon secondary exposure.

What is the function of the ciliary escalator in host defense?

It traps microbes in respiratory mucus and uses coordinated ciliary beating to transport them upward and away from the lungs.

Which antimicrobial enzyme is present in perspiration, tears, saliva, and tissue fluids, and what is its mode of action?

Lysozyme, which degrades bacterial cell walls.

What is the typical pH range of gastric juice that helps prevent microbial colonization?

$$1.2\text{ to }3.0$$

How do transferrins in the blood function as a chemical defense against pathogens?

They bind and limit the free iron available to microbes, inhibiting their growth.

What are the primary lymphoid organs and what occur within them?

The bone marrow (site of blood cell production and B cell development) and the thymus (site of T cell selection and differentiation).

What are the secondary lymphoid organs and what is their role in immunity?

The spleen, lymph nodes, and mucosal-associated lymphoid tissue (MALT/GALT), which serve as sites where mature lymphocytes interact with antigens to initiate adaptive immune responses.

Which granulocyte constitutes $50\text{--}70\%$ of healthy adult leukocytes and features a 3- to 5-lobed nucleus with fine lavender granules?

Neutrophils, which mediate respiratory bursts following phagocytosis.

What morphology and primary functions characterize eosinophils?

They possess a bilobed nucleus with large orange-red granules in pink-red cytoplasm; they mediate allergic responses and host defenses against helminthic parasite infections.

What is the primary function and identifying nuclear shape of monocytes?

Monocytes have a large, bean-shaped, dark purple nucleus; they circulate in the blood and migrate into tissues to develop into macrophages and dendritic cells.

What are the specific resident macrophage types found in the lungs, central nervous system, and liver?

Alveolar macrophages in the lungs, microglial cells in the central nervous system, and Kupffer cells in the liver.

How does Mycobacterium tuberculosis evade destruction by phagocytic cells?

It inhibits the fusion of the phagosome with the lysosome, preventing phagolysosome formation and enzymatic digestion.

By what mechanism does Listeria monocytogenes evade phagocytosis?

It lyses the phagolysosome membrane and escapes directly into the host cytoplasm to replicate.

What are the sequential steps of the inflammatory process following tissue damage?

Release of acute-phase proteins and inflammatory mediators (e.g., histamine, kinins, prostaglandins) by damaged cells $\rightarrow$ vasodilation and increased capillary permeability $\rightarrow$ phagocyte margination $\rightarrow$ diapedesis (extravasation) $\rightarrow$ phagocytosis of pathogens $\rightarrow$ tissue repair.

At what adult body temperature threshold is a fever classified as harmful, requiring initiation of treatment?

$$104.5^\circ\text{F}$$

What is the role of complement protein C3b in immune defense?

It coats the surface of microbial pathogens to act as an opsonin, greatly enhancing phagocytosis, and contributes to the formation of C5 convertase.

Which complement components assemble to form the Membrane Attack Complex (MAC), and what is its cytotoxic effect?

$C5b$, $C6$, $C7$, $C8$, and multiple $C9$ units, which create a transmembrane pore in the microbial plasma membrane leading to osmotic cytolysis.

What activates the classical, lectin, and alternative pathways of complement activation?

The classical pathway is activated by antigen-antibody complexes; the lectin pathway is activated by mannose-binding lectin binding microbial sugars; the alternative pathway is activated directly by pathogen surface components and spontaneous C3 cleavage.

How do Type I interferons (IFN-alpha and IFN-beta) protect host cells against viral spreading?

They are secreted by virus-infected cells and bind to receptors on adjacent uninfected cells, stimulating them to produce antiviral proteins that degrade viral mRNA and block viral protein synthesis.

What is an epitope (antigenic determinant)?

The specific localized structural domain on an antigen molecule that is recognized and bound by a specific B-cell receptor, T-cell receptor, or antibody.

What is the structural role of the Fc region of an antibody?

It constitutes the constant crystallizable fragment of the heavy chains that mediates effector functions such as binding cell surface receptors (e.g., on macrophages or NK cells) and activating complement.

Which immunoglobulin is the most abundant in serum ($80\%$), can cross the human placenta, and confers long-term immunity?

IgG

What structural features distinguish secretory IgA from other antibody classes?

It exists as a dimer containing two Ig monomer units linked by a J chain and a protective secretory component, enabling survival in mucosal secretions (saliva, tears, mucus, colostrum).

Which immunoglobulin class functions as a pentamer linked by a J chain with 10 antigen-binding sites, acting as the primary first responder in serum?

IgM

What genetic mechanism allows the immune system to generate up to $10^{15}$ different antibody specificities from only hundreds of genes?

Somatic recombination and rearrangement of variable (V), diversity (D), and joining (J) gene segments that encode the antigen-binding sites.

What is the immunological purpose of clonal deletion during lymphocyte maturation?

Negative selection that eliminates autoreactive B and T cells via apoptosis to ensure self-tolerance and prevent autoimmune disease.

What is the difference between T-independent and T-dependent B cell activation?

T-independent activation occurs when antigens with repeating epitopes (like polysaccharides) cross-link multiple B-cell receptors directly without T helper cells; T-dependent activation requires antigen internalization, presentation on MHC class II to CD4+ T helper cells, and costimulatory cytokine signaling.

What key structural organelle change distinguishes an activated plasma cell from a resting B cell?

A massive proliferation and dense network of rough endoplasmic reticulum dedicated to the high-rate synthesis and secretion of antibodies.

Which cytokines are secreted by Helper T 1 ($T_H1$) cells and what are their primary defensive functions?

They secrete interferon-gamma (IFN-$\gamma$), which activates macrophages and stimulates IgG production to eliminate intracellular pathogens.

What coreceptor and MHC molecule are used by cytotoxic T lymphocytes (CTLs) to identify target cells?

CD8 coreceptor interacting with abnormal or viral antigens presented on MHC class I molecules.

How do cytotoxic T cells and natural killer cells mediate antibody-dependent cell-mediated cytotoxicity (ADCC) against large parasites?

Antibodies (such as IgE or IgG) bind to parasite epitopes; effector cells (eosinophils, macrophages, or NK cells) bind the antibody Fc regions and release perforins, lytic enzymes, and cytotoxic cytokines externally onto the target.

How does the secondary (anamnestic) antibody response differ from the primary antibody response?

The secondary response has a shorter latent lag period, produces a much higher serum titer dominated by IgG rather than IgM, and exhibits increased affinity for the antigen.

What viral glycoprotein spikes mediate HIV attachment and fusion into host $CD4^+$ T cells?

gp120 binds to the CD4 receptor and a coreceptor (CCR5 or CXCR4), while gp41 mediates fusion of the viral envelope with the host cell membrane.

What blood concentration of $CD4^+$ T cells defines the clinical diagnosis of AIDS?

Fewer than $200\,\text{cells}/\mu\text{l}$

In what year was smallpox officially declared eliminated worldwide by global vaccination programs?

1980

What are the main advantages and clinical disadvantages of live attenuated vaccines?

Advantages: They replicate in the host, mimicking a natural infection to trigger strong cell-mediated and humoral responses often providing lifetime immunity with few doses. Disadvantages: They require cold storage, cannot be safely given to pregnant or immunocompromised individuals, and carry a rare risk of reversion to virulence.

What defines a conjugated vaccine?

A vaccine in which a poorly immunogenic capsular polysaccharide is chemically linked to a protein carrier to enhance T-dependent immunogenicity (e.g., Hib and Prevnar).

How do mRNA vaccines (such as the Pfizer and Moderna SARS-CoV-2 vaccines) trigger immunity?

Lipid nanoparticles deliver mRNA encoding the viral spike protein into host cells, where host ribosomes translate the antigen in the cytoplasm; the mRNA rapidly degrades without entering the nucleus or integrating into host genomic DNA.

What is herd immunity?

The indirect protection of unimmunized, susceptible individuals from an infectious pathogen that occurs when a high proportion of the population is immune.

Based on the hemagglutination blood typing test card shown in the figure, what is the patient's blood type?

AB negative ($\text{AB}^-$), as shown by agglutination with Anti-A and Anti-B antibodies, lack of agglutination with Anti-D (Rh negative), and a negative control.

How are monoclonal antibodies produced using hybridoma technology?

Short-lived, antigen-primed antibody-producing B cells isolated from an immunized animal are fused with immortal myeloma (cancer) cells to create hybridomas, which are screened (e.g., via ELISA) and cloned to continuously secrete a single epitope-specific antibody.

Why is anti-CD20 monoclonal antibody therapy effective against B-cell Non-Hodgkin's lymphoma without eradicating the B-cell lineage permanently?

CD20 is expressed on mature and malignant B cells, marking them for targeted death, but hematopoietic stem cells lack CD20 and can regenerate healthy mature B cells after treatment.

What is the molecular target and mechanism of action of the monoclonal antibody drug Fasenra (benralizumab)?

It binds CD125 (IL-5R$\alpha$) on eosinophils, blocking IL-5 binding and recruiting NK cells through its Fc region to trigger eosinophil apoptosis in eosinophilic asthma.

What is the targeted self-antigen in Graves' disease?

Thyroid-stimulating hormone (TSH) receptor.

What molecular defects cause X-linked severe combined immunodeficiency (X-SCID) and ADA-SCID?

X-SCID is caused by a defective IL-2 receptor gamma chain, whereas ADA-SCID is caused by a deficiency in the adenosine deaminase enzyme; both result in a loss of both functional B and T lymphocytes.