203 Exam 5 Concepts Review: Understanding Immune Responses and Pathogen Interaction

How/when/in which populations does a true pathogen cause an infection? What about an opportunistic pathogen?

Infects healthy individuals, causing disease (e.g., flu virus). Opportunistic Pathogen: Usually harmless but infects when immune system compromised (e.g., Candida albicans).

Humans have a symbiotic relationship with their normal microbiota. Describe the benefits that both organisms gain from this association.

Humans benefit from microbiota for digestion, vitamin production, and immune system education. Microbiota gain nutrients and a niche.

What types of virulence factors make a pathogen more dangerous?

Toxins damage tissues, adhesion factors help in colonization, invasion factors aid tissue invasion, immune evasion factors evade host defenses.

What does the typical pattern of infection look like?

Includes incubation (exposure to symptom onset), prodromal (non-specific symptoms), acute (peak symptoms), convalescent (recovery), and resolution (elimination).

How do epidemiologists trace where an infection came from?

Done via contact tracing, genetic analysis, environmental investigation, and surveillance for patterns and sources.

What is a nosocomial infection? Which areas of the body/types of patients are most susceptible? What can hospitals do to reduce their occurrence?

Acquired in hospitals, affecting surgical, urinary, and respiratory sites. Risk for those with weakened immune systems. Prevented by hygiene, sterilization, and isolation practices.

Describe the first, second, and third lines of defense. How do they overlap and interact with each other? Why is this redundancy important?

First Line: Physical and chemical barriers.

Second Line: Innate immune cells and inflammation.

Third Line: Adaptive immune response.

Overlap and Interaction: Innate responses can activate adaptive responses for redundancy.

Describe each white blood cell or leukocyte and how it functions in the immune system. Do any cells have both innate and adaptive functions?

Neutrophils: Phagocytosis.

Macrophages: Phagocytosis, antigen presentation.

Dendritic Cells: Antigen presentation.

NK Cells: Kill infected cells.

B Cells: Produce antibodies.

T Cells: Helper T cells assist, cytotoxic T cells kill.

Innate-Adaptive Cells: Dendritic cells bridge both immunities.

How does the lymphatic system work and how does it participate in the immune response?

Collects and filters lymph.

Transports immune cells and antigens to lymph nodes.

Describe the 4 basic steps of phagocytosis. Which cells are capable of phagocytosis?

Chemotaxis: Phagocytes attracted to infection.

Adherence: Phagocyte attaches to pathogen.

Ingestion: Pathogen engulfed in phagosome.

Digestion: Phagosome fuses with lysosome for digestion.

Cells Capable: Neutrophils, macrophages, dendritic cells.

Describe extracellular killing. Which cells are capable of extracellular killing?

Killing pathogens outside cells.

Cells: NK cells, eosinophils.

Describe how interferon is activated and how it participates in the immune response.

Activated by viral RNA or immune cells.

Stimulates antiviral protein production.

Enhances immune response.

Describe how complement is activated and how it participates in the immune response.

Activated by pathogens or antibodies.

Enhances phagocytosis, triggers inflammation, and lyses pathogens.

Describe how an antibody interacts with an antigen.

Antibodies bind to specific antigens, neutralizing or marking them for destruction.

How are T-cells educated in the thymus and B-cells educated in the bone marrow? Discuss the process of clonal deletion

T-cells: Educated in the thymus, undergo clonal deletion to remove self-reactive cells.

B-cells: Educated in the bone marrow, undergo clonal deletion of self-reactive cells.

How does a B-cell respond to activation/sensitization in the absence of T-cell involvement? What changes if a T-cell is involved?

Without T-cell: B-cells can be activated directly, leading to antibody production.

With T-cell: T-cell help enhances B-cell response for more efficient antibody production.

Which cells are capable of antigen presentation? Describe the process.

Cells: Dendritic cells, macrophages, B cells.

Process: Antigens are presented on MHC molecules after being digested by antigen-presenting cells.

How is the primary response different from the secondary response?

Primary Response: First encounter with antigen, slower and produces lower antibody levels.

Secondary Response: Subsequent encounters, faster and stronger due to memory cells.

Describe how a cytotoxic T-cell interacts with antigen presented in MHC I. Describe how a helper T-cell interacts with antigen presented in MHC II.

Cytotoxic T-cell (MHC I): Kills infected cells presenting antigens on MHC I.

Helper T-cell (MHC II): Activates other immune cells when antigens are presented on MHC II.

How does active immunity differ from passive immunity? Describe two examples of each.

Active Immunity: Develops after exposure to antigens, e.g., through vaccination.

Passive Immunity: Temporary immunity from receiving antibodies, e.g., from mother to fetus.

What is a vaccine? Why are most recommended in the first few years of life?

Definition: Substance containing weakened pathogens or antigens to stimulate immune response.

Timing: Recommended in early life to protect during immune system development.

True Pathogen

a microbe capable of causing infection & disease in healthy persons with normal immune defenses. They can bypass host defenses and lead to illness.

Normal flora/microbiota

The native types of bacteria, fungi, & viruses that normally reside on the body. Also known as Normal Flora.

Pathogenicity

The capacity of microbes to cause disease.

Virulence

In infection, the relative capacity of a pathogen to invade and harm host cells.

Infectious dose

the estimated number of microbial cells or units required to establish an infection.

Virulence factors

A product of microbes such as an enzyme or toxin that increases the microbe’s invasiveness or pathogenicity.

Incubation period

the period of time from the initial contact with an infectious agent to the appearance of the first symptoms.

Period of invasion

the period during a clinical infection when the infectious agent multiplies at high levels, exhibits its greatest toxicity, and becomes well established in the target tissues.

Convalescent period

recovery; the period between the end of a disease and the complete restoration of health in a patient.

Chronic infection

an infection that persists over a long duration, with symptoms being mild or absent.

Reservoir

in epidemiology, the natural host or habitat of a pathogen that is long term origin.

Carriers

a person who asymptomatically harbors infectious agents and inconspicuously spreads them to others.

Vectors

an animal that transmits infectious agents from one host to another, often biting or piercing arthropod such as the tick, mosquito, or fly, bit it can also include birds & mammals. Vectors convey infectious agents mechanically by simple contact or biologically, with the parasite developing in the vector.

Zoonoses

an infectious disease indigenous to animals that humans can acquire through direct or indirect contact with infected animals.

Communicable disease

when infected host can transmit the infectious agent to another host & establish infection in that new host.

Fomite

an inanimate object that harbors & transmits pathogens.

Epidemic

a sudden & simultaneous increase in the number of cases of a certain disease in a community.

Pandemic

an epidemic that has spread across a wide geographic area, including more than one continent or international border, & can extend to a worldwide occurrence.

Nosocomial

diseases that are acquired or developed during a hospital stay.

Opportunistic pathogen

a microbe that infects a host when the body’s defense system is vulnerable, causing opportunistic infection.