INFECTION AND DEFENSE MECHANISM DEFECTS

Flashcards covering infection, pathogenicity, microbial classifications, immune response mechanisms, hypersensitivity reactions, and immunodeficiencies based on lecture study notes.

What is the difference between bacterial colonization and infection?

• Colonization occurs when good bacteria develop in an area without causing physical or pathological harm to the body

• infection occurs when a bad bacteria/pathogen invades the body and can cause disease.

What three factors determine the overall pathogenicity of a pathogen?

communicability (how easily a pathogen is spread)

Infectivity (how sick you get from the pathogen)

virulence (how badly the pathogen can cause disease).

How is immunogenicity defined?

how the body produces an immune response.

What are antigens and antibodies?

• antigen = any molecule or structure that the immune system can recognize

• Antibodies = Y-shaped proteins that the immune system synthesizes to bind specific antigens.

What are prions and how do they cause disease?

non-living, infectious misfolded proteins that cause regular proteins in the host to also misfold.

What is the pathophysiological mechanism of a viral infection?

Viruses enter host cells → integrate their genetic material into host DNA → hijack cellular protein synthesis → replicate rapidly → cause cell lysis

How do Gram-positive and Gram-negative bacteria differ structurally and in staining?

• Gram-positive bacteria stain purple due to a single thick, encapsulated peptidoglycan cell wall

• Gram-negative bacteria do not stain due to an additional outer membrane layer (2 walls), making them structurally resilient ("armored tanks"), highly destructive, and capable of hiding from immune cells.

What is the difference between exotoxins and endotoxins?

• Exotoxins are toxins secreted outwards by living bacteria to defend against the host immune system

• Endotoxins are structural toxins contained inside bacterial cells that are released strictly when bacteria are destroyed and lysed by immune attacks.

What are the phases of the stereotypical disease course?

Incubation Period

Prodromal Phase

Acute Phase

Convalescence

potentially Chronic Disease or Critical threshold (death).

What characterizes the prodromal phase of an infection?

The initial appearance of mild, highly non-specific local and systemic clinical symptoms (generalized yuckiness) resulting from early tissue injury and inflammatory signaling.

What are the core characteristics and cell types of innate immunity?

Innate immunity is present at birth (congenital), provides an immediate/rapid response, and triggers localized inflammation

Its cells include phagocytic cells (monocytes/macrophages, granulocytes like neutrophils, eosinophils, basophils, and dendritic cells), natural killer cells, mast cells, and cytokines.

What are the five distinct antibody classes, and which is primary in neutralizing pathogens?

The five distinct antibody classes are IgG, IgA, IgM, IgE, and IgD

IgG is the primary circulating antibody class responsible for neutralizing pathogens.

What are the roles of Cytotoxic T cells and Helper T cells in cell-mediated immunity?

Cytotoxic (killer) T cells directly destroy infected cells and tumor cells

Helper T cells assist in orchestrating the overall immune response.

What is the difference between positive selection, negative selection, and self-tolerance?

Positive selection is a quality check in the thymus and bone marrow ensuring cells work properly before being stored in lymph nodes

Negative selection eliminates improperly working or self-reactive cells to prevent autoimmune disease

Self-tolerance is the body's ability to recognize which cells must be eliminated during negative selection.

How do Antigen Presenting Cells (APCs) activate T cells?

APCs (macrophages and dendritic cells) eat pathogens, display surface antigen fragments on MHC class II receptors, travel to lymph nodes, and scan naive T cells until finding a matching T-cell receptor (TCR) to trigger clonal proliferation.

How do primary and secondary immune responses differ regarding vaccination?

Primary immune response (vaccination) bypasses live pathogen infection by introducing isolated antigens intramuscularly

Secondary immune response (booster shots) allows memory B cells to respond immediately and produce high levels of plasma antibodies before disease is encountered.

How are hypersensitivity reactions categorized by target antigen?

Allergy (over-activated against exogenous environmental antigens)

Autoimmunity (over-activated against endogenous self-antigens/self-proteins)

Alloimmunity (over-activated against foreign human tissues)

What defines Type I hypersensitivity reactions?

Type I reactions are immediate IgE-mediated allergic reactions triggered by exogenous antigens that cause a histamine response, requiring a prior sensitizing event.

What defines Type II hypersensitivity reactions?

tissue-specific, antibody-mediated (IgG/IgM) cytotoxic reactions

cell destruction by complement/antibodies, phagocytosis, ADCC, or target cell malfunction (e.g., myasthenia gravis).

What defines Type III hypersensitivity reactions?

immune complex-mediated (IgG/IgM) systemic, non-organ specific reactions where free-floating antigen-antibody complexes stick to tissue walls (e.g., serum sickness).

What defines Type IV hypersensitivity reactions?

cell-mediated (T-cell driven) delayed-type reactions that do not involve antibodies (e.g., TB skin test, poison ivy or metal contact allergies, graft rejection, Multiple Sclerosis).

What are primary immunodeficiencies and what are four examples?

Primary immunodeficiencies are congenital/genetic inherited defects in immune cell development.

Examples include Hypogammaglobulinemia (selective B-cell deficiency), Severe Combined Immunodeficiency (SCID; absence of functional T and B cells), Complement Deficiencies (C3 or C5 genetic deficiency), and Chronic Granulomatous Disease (CGD; phagocyte deficiency).

What are the physiological/environmental and pathological/medical causes of acquired immunodeficiencies?

Physiological/environmental causes include pregnancy, advanced aging, and eating disorders

Pathological/medical causes include leukemia/lymphoma and diabetes mellitus.

How are disease diagnosed?

• signs and symptoms

  • local/specific symptoms

  • systemic/non-specific symptoms

• infection site

• microbial culture through swabbing

• molecular and serum blood testing

What are the two types of adaptive immunity, what do they produce and where are they produced?

• cell-mediated immunity

  • T cells (cytotoxic/helper) made in thymus

• Humoral immunity (released in bloodstream)

  • B cells made in bone marrow

How do APCs activate B cells?

• APCs eat pathogen at infection site, memorize them, and display surface antigen fragments on their surface MHC class II receptor

• APCs travel from tissue to lymph node

• at lymph node, APCs scan naive B cells until it finds its matching BCR (B cellreceptor)

• once matched, APC activates B cell

• activated B cell and activated helper T cell starts producing antibodies