The Nature of Immunity – Lecture Review

These flashcards cover key concepts from the lecture "The Nature of Immunity," including definitions, immune system features, barriers, pathogen recognition, innate and adaptive mechanisms, complement, inflammation, and stages of immune responses.

What is an antigen?

Any substance that elicits an immune response.

What molecule specifically reacts with an antigen?

An antibody.

How many major classes of human pathogens are there?

Four – viruses, bacteria, fungi, and parasites (including protozoa and helminths).

List the three cardinal features of immunity.

Specificity, memory, and self-discrimination (tolerance of self).

Name the three levels of host defense against pathogens.

Physical barriers, innate immune system, and adaptive immune system.

Which level of immunity provides the fastest response to infection?

The innate immune system (minutes to hours).

Which level of immunity improves in quality with each exposure to the same antigen?

The adaptive immune system.

State two examples of physical barriers to infection.

Intact skin and mucosal epithelial surfaces (e.g., respiratory or gastrointestinal mucosa).

How does normal body temperature act as a physiologic barrier?

It inhibits growth of many microorganisms; fever can further inhibit pathogens.

Why does the low pH of the stomach, skin, and vagina protect against infection?

Most microbes cannot grow or survive under acidic conditions.

Give two common mucosal routes of pathogen entry.

Mouth/respiratory tract and gastrointestinal tract.

Which pathogens are transmitted by insect vectors penetrating external epithelia?

Examples include Plasmodium spp. (malaria) by Anopheles mosquitoes and Flavivirus (yellow fever) by Aedes mosquitoes.

What are PAMPs?

Pathogen-associated molecular patterns—conserved molecular signatures shared by many pathogens.

What type of host receptors detect PAMPs?

Pattern-recognition receptors (PRRs).

Give one example of a PRR family and a ligand it recognizes.

Toll-like receptor 4 (TLR4) recognizes bacterial lipopolysaccharide (LPS).

Which TLR recognizes double-stranded viral RNA within endosomes?

TLR3.

Name three resident macrophage populations that belong to the Mononuclear Phagocytic System.

Microglia (brain), Kupffer cells (liver), and alveolar macrophages (lung).

Place the following steps of phagocytosis in the correct order: adherence, phagosome formation, phagolysosome formation, degradation.

Adherence → phagosome formation → phagolysosome formation → degradation of pathogen.

What are the three pathways that activate complement component C3?

Classical, lectin, and alternative pathways.

Which complement fragments are powerful anaphylatoxins that can trigger mast-cell degranulation?

C3a and C5a.

List two vasoactive mediators released from mast-cell granules.

Histamine and proteoglycans (e.g., heparin).

Which cytokine-induced changes in blood vessels lead to the redness and heat of inflammation?

Vasodilation and increased vascular permeability.

During adaptive immunity, which cells capture antigen in peripheral tissues and migrate to lymph nodes to present it?

Dendritic cells.

Distinguish humoral from cell-mediated adaptive immunity in terms of principal effector cells.

Humoral immunity → B cells/antibodies; Cell-mediated immunity → T cells (helper and cytotoxic).

What are the approximate time frames for the three stages of an immune response after infection?

Immediate innate (0–4 h), early induced innate (4–96 h), and adaptive (>96 h).

Define clonal deletion.

The removal of self-reactive immature lymphocytes during development to maintain self-tolerance.

Which effector mechanism is most important for eliminating extracellular bacteria?

Phagocytosis aided by opsonizing antibodies and complement.

Which innate lymphocyte kills virus-infected cells without prior sensitization?

Natural killer (NK) cell.

Name two cytokines that inhibit viral replication in host cells.

Type I interferons: IFN-α and IFN-β.

State one requirement of an effective immune system related to pathogen diversity.

Possession of a vast range of antigen receptors to recognize diverse pathogens.

How does the recognition repertoire differ between innate and adaptive immunity?

Innate repertoire is inherited and fixed; adaptive repertoire is somatically generated and highly variable.

Why is the adaptive response faster on second exposure to the same pathogen?

Because memory B and T cells formed during the primary response respond more rapidly and robustly.

Summarize the main threat posed by intracellular cytosolic infections and the adaptive cell type that counters it.

Viruses and some bacteria replicate in the cytosol; cytotoxic T lymphocytes (CTLs) recognize infected cells and induce apoptosis.

What are the learning objectives covered in this lecture?

Threats of various pathogens, cardinal features of immunity, defense levels, innate responses and pathogen recognition, adaptive responses, and comparison of innate versus adaptive immunity.