Microbio Exam 2 Short Answers

Name and describe three ways antibodies function to eliminate antigens.

1. Neutralization: Antibodies bind to viruses, toxins, or other pathogens and block them from attaching to or entering host cells, preventing them from causing harm

2. Activating Complement: Opsonization, Membrane Attack Complex (MAC) (lysis), Inducing inflammation

3. Increase Phagocytosis: Opsonization, Agglutination, Precipitation

Describe how the two types of MHCs present antigens.

Major Histocompatibility Complex: “Self” proteins for T cell recognition

MHC I

• Displayed on all nucleated human cells

• Binds to and displays antigens that originate in the cytoplasm

• Process:

  • A cell is infected by an intracellular pathogen

  • The cell breaks down the virus into small pieces (proteasome)

  • MHC I displays a piece of the pathogen’s on the cell’s surface

  • A CD8+ cytotoxic T cell recognizes it

  • T cell kills infected cell

• Purpose: Allows the immune system to identify and eliminate infected or abnormal host cells.

Remember: MHC I → inside the cell → CD8 T cell → kills infected cell.

MHC II

• Expressed in only 3 cell types

  • Macrophages, Dendritic Cells, B Cells

    • AKA - Antigen Presenting Cells (APCs)

• Binds to and displays antigens that originate outside the cell

• Process:

  • An Antigen Presenting Cell (APC) engulfs an extracellular pathogen

  • The APC breaks down the pathogen (phagolysosome)

  • MHC II displays a part of the pathogen on the surface of the cell

  • A CD4+ helper T cell recognizes

  • The helper T cell activates and coordinates other immune cells to fight the infection

• Purpose: Activates T helper cells, which stimulate B cells, macrophages, and other immune cells to fight extracellular pathogens.

Remember: MHC II → outside pathogen → CD4 T cell → coordinates immune response.

Differentiate T helper cells from T cytotoxic cells: include details on co-receptors, activation signal, function and process of eliminating antigen.

T helper cells

• CD4 co-receptor

• T-cell receptors recognize MHC II

• Recognize an MHC II complex on an APC

• Releases cytokines to activate and regulate B cells, cytotoxic T cells, and macrophages

• Coordinates other immune cells that eliminate pathogens

T cytotoxic cells

• CD8 co-receptor

• Recognize an MHC I complex on an infected cell or other appropriate presenting cell

• Kill infected host cells

• Release perforins and granzymes, causing the target cell to undergo apoptosis

For each type of lymphocyte (cytotoxic T cells, T helper cells and B cells), describe the specific steps in lymphocyte activation, function, and type of antigen eliminated.

Cytotoxic T cells (CD8+)

• Activation

  • An infected nucleated cell displays an MHC I molecule

  • Cytotoxic T cells recognize the MHC I molecule

  • The cytotoxic T cell binds and activates the cell

  • The activated CD8+ cell proliferates (clonal expansion) and differentiates into effector and memory cells

• Function and Elimination

  • Effector cytotoxic T cells release perforins and granzymes, triggering apoptosis of the infected host cell

  • They can also release cytokines that attract macrophages

  • Target: Intracellular pathogens, killing the pathogen helps eliminate replication of pathogen

T helper cells (CD4+)

• Activation

  • An APC engulfs an extracellular pathogen and processes its antigens

  • APC displays MHC II molecule

  • A specific T helper cells recognizes the MHC II molecule through its TCR and CD4 receptors

  • Clonal expansion and differentiation occurs into effector and memory T cells

• Function and Elimination

  • Effector T helper cells release cytokines that activate and regulate B cells, cytotoxic T cells, and macrophages

  • Help B cells produce antibodies and enhance other immune defenses

  • Target: Extracellular pathogens through activation and coordination. T helper cells coordinate elimination rather than directly killing the pathogen

B cells (B lymphocytes)

• Activation

  • A B-cell receptor binds to a specific free antigen

  • The B cell internalizes the antigen, processes it, and presents is epitope on MHC II

  • A specific T helper cell recognizes the MHC II molecule and releases cytokines that stimulate the B cell

  • Activated B cell proliferates and differentiates into antibody-secreting plasma cells and memory B cells

• Function and Elimination

  • Plasma cells secrete antibodies (immunoglobulins), which circulate through blood and lymph

  • Antibodies neutralize pathogens or toxins, promotes phagocytosis through opsonization, and clumps antigens through agglutination

  • Memory B cells enable a faster, stronger response during future exposure

  • Target: Extracellular pathogens and toxins

Compare and contrast humoral and cell-mediated adaptive immunity. Mention the following:
i. Eliminates extracellular or intracellular antigens
ii. Involves B, TH and or TC cells
iii. Antigen-presentation via MHCI or MHCII
iv. Mechanism for eliminating pathogen
v. Which is transferrable from one human to another?

Humoral Immunity

• Extracellular

• B cells and T helper cells

• MHC II presents extracellular epitopes to CD4+ T helper cells

• Elimination: B cells become plasma cells and release antibodies that neutralize, opsonize, or agglutinate antigens

• Provides artificial passive immunity (can be transferred through blood products)

Cell-mediated Immunity

• Intracellular

• Cytotoxic T cells; T helper cells can help coordinate the response

• MHC I

• Cytotoxic T cells induce apoptosis in infected host cells

• Not ordinarily transferred as a ready-made, lasting protective response through routine antibody transfer

Key distinction: Humoral immunity uses antibodies to target extracellular threats, whereas cell-mediated immunity uses T cells to eliminate infected host cells containing intracellular pathogens.

Both are branches of adaptive immunity and can generate memory cells for faster responses to future exposure.

Describe the use of immunological methods for diagnosing infectious
disease. Include: principle (how it works), TAT, one advantage, one
disadvantage, and give one example.

Principle: Immunological tests use specific antigen-antibody interactions to detect either antigens from a pathogen or antibodies produced by the patient.

TAT (Turnaround Time): Approximately 5 minutes to a few hours

Advantage: Inexpensive, low tech, easy to use, and fast

Disadvantage: They generally have lower sensitivity and specificity than culture. Cross-reactions can cause inaccurate results and antibody tests may not distinguish a current infection from a past infection

Example: ELISA for HIV, the patients blood is tested for antibodies against HIV, if antibodies are present they bind to the corresponding antibody test. An enzyme reaction produces a measurable color change indicating a positive result.

Describe polymerase chain reaction (PCR), real-time PCR, and reverse
transcription PCR (RT-PCR) and state a clinical applications of each.

Polymerase Chain Reaction (PCR)

• Repeated cycles of DNA replication amplify a specific DNA sequence, creating millions or billions of copies. Primers determine which DNA sequence is amplified

• Clinical Application: Detecting bacterial DNA in a patient sample or testing for genetic disorders

Real-time PCR (qPCR)

• Amplifies DNA while monitoring the amount of amplified product during each cycle using a fluorescent signal. Allows the amount of target DNA to be measured

• Clinical Application: Detecting and estimating the amount of a pathogen’s DNA in a clinical sample

Reverse transcription PCR (RT-PCR)

• Uses the enzyme reverse transcriptase to convert RNA into complementary DNA (cDNA) which is then amplified by PCR

• Clinical Application: Detecting RNA viruses such as SARS-CoV-2

A patient tells a nurse, "I'm not sure I want to get this vaccine. I've heard that vaccines are unsafe, and I don't think I really need it because I'm unlikely to get the disease." (5 points)
• Define vaccine hesitancy in your own words.
• Identify two different factors that can contribute to vaccine
hesitancy. Please identify only factors that are based on science-
based misinformation (not religious or cultural practices).
• As a future nurse, provide a scientific explanation that would address
patient concerns when communicating with a vaccine-hesitant
patient.

Vaccine Hesitancy: A patient who has their own understanding and beliefs about vaccines, who may be hesitant or refuse to receive one.

Two factors:

• False claim that vaccines cause autism: Originated from a study of 12 patients, later retracted. Scientific evidence doesn’t support a link between the MMR vaccine and autism

• The belief that vaccines are more dangerous than the disease they prevent: People may overestimate the risk of vaccine side effects and underestimate the risk of infection, complications, and transmissions

As a future nurse I would ask what the patient has heard about vaccines and their thoughts. I would explain that vaccines introduce specific non-disease causing antigens into their immune system, that then is attacked by it and creates memory cells, so if the patient does come in contact with that certain disease, it can allow a faster immune response and reduce severity.

List 3 reasons why an immune response to an infection makes you tired. How might this explain how/why people feel sick after receiving a vaccine?

Cytokine release:

• Immune signaling molecules communicate with the brain and promote sickness behaviors such as fatigue and reduced motivation

Energy expenditure:

• Activating immune cells, producing immune molecules, and repairing damaged tissues require energy that would otherwise support normal activities

Changes in body temperature and metabolism

• Fever increases the body’s metabolic demands, contributing to weakness and tiredness

Connection to Vaccines:

• Vaccines activate the immune system to start releasing cytokines and other immune responses, which in turn can cause temporary fatigue, fever, or muscle aches

Define “pyrogen” and how they function in the fever response.

Pyrogen: A fever-inducing substance that triggers the release of cytokines involved in fever response

• Pyrogens stimulate immune cells to release cytokines

• These signals act on the hypothalamus (brain region that regulates body temp)

• Hypothalamus raises the body’s temperature set point, producing fever

An extremely high fever can damage cellular enzymes and proteins

Define self-tolerance and describe how and why the body screens immature T and B cells for this feature.

Self-tolerance is the immune system’s ability to recognize the body’s own cells and molecules as self to avoid attacking them

• T-cell screening: Immature T cells develop in thymus and are screened for their ability to recognize self-MHC and self-antigens. Cells that fail this screening undergo apoptosis

• B-cell screening: Immature B cells develop in bone marrow and are tested for self-reactivity. Strong self-reactive cells are altered or undergo apoptosis

• Purpose: Helps prevent the immune system from attacking healthy tissues

• Clinical importance: FAILED SELF-TOLERANCE = AUTOIMMUNITY

Describe the following fever classifications and provide an example of an
infection that would result in that fever pattern.
• Fever of undetermined origin
• Relapsing fever
• Tertian fever

• Fever of undetermined origin (FUO)

  • A persistent or recurrent fever for which the cause remains unidentified despite appropriate investigation (101F, persistent of 3 weeks, 1 week inpatient study)

  • Example: A patient still has a prolonged fever that remains unexplained after diagnostic testing (Hodgkins lymphoma can cause prolonged fever)

• Relapsing fever

  • Episodes of fever alternate with periods where the body temperature returns toward normal

  • Example: Caused by Borrelia species (bacteria capable of causing recurring fever episodes)

• Tertian fever

  • A fever pattern in which fever episodes recur approximately every 48 hours, congenitally described as occurring on alternate days

  • Example: Malaria caused by Plasmodium vivax, which can produce a tertian fever pattern

Define “superantigen”. Describe what type of virulence factor they are and how superantigens activate T helper cells.

Superantigen: A microbial toxin that causes unusually widespread, nonspecific activation of T cells

Type of virulence factor: A secreted toxin that interacts with normal immune regulation (staphylococcus)

A superantigen binds to MHC II on an APC and to the TCR, bypassing normal specificity and activates multiple helper T cells simultaneously

Excessive cytokine release can cause widespread inflammation, fever, low BP, and potentially toxic shock

Discuss why smallpox is considered one of the deadliest viruses in human history by integrating the following elements into your answer. (10 points)
• Mode of transmission
• Incubation period (in days)
• Tropism and first cell type infected
• Two innate immune defenses inactivated
• Mortality rate and reservoir
• Year of eradication

Smallpox is caused by the various virus and was historically devastating because it spread between people, caused severe systemic disease, and had a high mortality rate.

• Modes of transmission: Primarily through respiratory droplets and aerosols during close contact with an infected person, as well as infected bodily fluids, skin lesions, or contaminated materials

• Incubation period: Usually about 10-14 days, approximately 7-17 days before symptoms appear USUALLY 12 DAYS

• Tropism and first cell type infected: The virus initially infects cells in the respiratory tract following inhalation (THROAT). Dendritic cells and other immune cells can become involved early and help the virus spread. Variola has a broad tissue tropism, eventually affecting multiple tissues including skin.

• Two innate immune defenses inactivated: Variola produces proteins that interfere with interferon-mediated antiviral defenses and complement-mediated immune defenses. Interferons normally help cells resist viral replication, while complement helps eliminate pathogens and promote inflammation.

• Mortality Rate: Historically, ordinary smallpox killed approximately 30% of infected, unvaccinated individuals. although mortality varied by disease form.

• Reservoir: Humans were the only natural reservoir of variola virus. There is no established animal reservoir, which helped make eradication possible.

• Year of eradication: 1980