Chapter 08: Infection and Defects in Mechanisms of Defence

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Questions and Answers

What characterizes congenital immunodeficiencies?

Caused by genetic defects (correct)

Caused by infections

Caused by environmental factors

Always present at birth (correct)

Which type of infection is most common in individuals with defects in cell-mediated immune response?

Fungal infections (correct)

Viral infections (correct)

Bacterial infections

Parasitic infections

What is the primary issue in severe combined immunodeficiency (SCID)?

Total lack of T-cell function (correct)

Decreased phagocyte function

Inadequate production of IgG

Excessive B-cell activity

Which syndrome is associated with complete or partial lack of the thymus?

DiGeorge syndrome Signup and view all the answers

What is a common cause of acquired immunodeficiency?

Malnutrition Signup and view all the answers

What is the mechanism behind type I hypersensitivity reactions?

IgE-mediated mast cell degranulation Signup and view all the answers

What characterizes type II hypersensitivity reactions?

Tissue-specific immune responses Signup and view all the answers

Which type of hypersensitivity reaction is characterized by delayed response?

Type IV hypersensitivity Signup and view all the answers

What defines alloimmunity?

Immune reaction against antigens from another individual Signup and view all the answers

Which treatment is typically used for antibody deficiencies?

Replacement of missing immunoglobulins Signup and view all the answers

What are exotoxins, and how do they affect host cells?

Exotoxins can damage plasma membranes or inactivate critical enzymes. Signup and view all the answers

What is septicemia, and what consequence does it have on the body?

Septicemia causes increased blood vessel permeability leading to hypotension. Signup and view all the answers

How do viruses proliferate within host cells?

By using the metabolic processes of host cells. Signup and view all the answers

Which description accurately identifies pathogens that cause mycoses?

They include unicellular yeasts and multicellular moulds. Signup and view all the answers

What is the role of dermatophytes in infection?

They infect the skin, hair, and nails. Signup and view all the answers

How are parasitic and protozoal infections primarily transmitted?

Via vectors like mosquitoes or contaminated food and water. Signup and view all the answers

What is the most common cause of fungal infections in humans?

Candida albicans Signup and view all the answers

What characterizes an immune deficiency?

The failure of self-defense mechanisms to function properly. Signup and view all the answers

Which infection control measure does not directly target pathogen entry?

Increasing the number of healthy bacteria in the gut. Signup and view all the answers

What is a primary function of endotoxins released by bloodborne bacteria?

To activate the inflammatory response. Signup and view all the answers

Study Notes

Infection

Infectious diseases are major contributors to global morbidity and mortality rates.
Pathogens possess distinct characteristics that affect their disease-causing potential.
Bacteria injure host cells via exotoxins (enzymes damaging cell membranes or inhibiting protein synthesis) and endotoxins (triggering inflammation and fever).
Septicemia indicates bacteria multiplication in blood, where endotoxins induce vasoactive enzyme release, leading to increased vascular permeability and potential endotoxic shock.
Viruses infiltrate host cells and exploit their metabolic systems to replicate and induce disease.
Infected cells may experience reduced protein synthesis, lysosomal disruption, formation of viral nucleic acid inclusions, giant cell formation, altered antigen properties, potential malignant transformation, or increased susceptibility to bacterial infections.
Mycoses are fungal infections, classified into yeasts (single-celled) and multicellular moulds (filaments).
Dermatophytes infect skin, hair, and nails, causing conditions like ringworm and athlete's foot.
Fungi, such as Candida albicans, emit toxins and enzymes harmful to tissues; Candida is the leading cause of fungal infections in humans.
Parasitic organisms vary from unicellular protozoa to larger worms and are prevalent globally, but less so in Canada and the U.S.
Transmission of parasites mainly occurs via vectors (e.g., mosquitoes) or contaminated food/water, with diseases like malaria and Chagas disease as notable examples.
Infection control requires safe food and water, waste management, insect control, vaccination, prudent antimicrobial use, and passive immunotherapy.

Deficiencies in Immunity

Immune deficiencies occur when self-defense mechanisms fail to function normally.
Immunodeficiencies are either congenital (genetic origin disrupting lymphocyte development) or acquired (due to diseases or physiological changes).
Clinical hallmark is susceptibility to rare or severe infections, with infection types correlating with specific immune defects.
Individuals with cell-mediated immunity defects experience fungal and viral infections; those with humoral defects face bacterial infections.
Severe Combined Immunodeficiency (SCID) signifies a total absence of T-cell function and significant B-cell dysfunction.
Wiskott-Aldrich syndrome is linked to reduced IgM antibody production.
DiGeorge syndrome results from a partial or complete absence of the thymus, impacting T-cell immunity and often associated with hypocalcemia and cardiac issues.
Antibody deficiencies arise from issues in B-cell maturation or function, as observed in Bruton agammaglobulinemia or selective IgA deficiency.
Phagocyte defects can arise from inadequate quantities or dysfunctions, affecting bacterial adhesion and killing.
Deficiencies in complement proteins and mannose-binding lectin are rare but present a higher infection risk.
Acquired immunodeficiencies stem from conditions like malnutrition, medical treatments, trauma, stress, or infections.
Treatments typically involve replacement therapies for deficient antibodies or lymphocytes, with ongoing gene therapy trials.
Acquired Immunodeficiency Syndrome (AIDS) is caused by the retrovirus HIV, targeting and destroying CD4+ Th cells.

Hypersensitivity: Allergy, Autoimmunity, and Alloimmunity

Hypersensitivity involves misdirected immune responses either against self-tissues (autoimmunity), beneficial foreign tissues (alloimmunity), or exaggerated reactions to environmental antigens (allergy).
Hypersensitivity mechanisms include type I (IgE-mediated), type II (tissue-specific), type III (immune complex-mediated), and type IV (cell-mediated).
Reactions can be immediate (occurring within seconds to hours) or delayed (taking hours to days).
Anaphylaxis is a rapid, severe immediate hypersensitivity reaction that can lead to shock and death upon re-exposure to antigens.
Type I hypersensitivity occurs when an allergen binds to IgE on mast cells, triggering degranulation and release of histamine.
Type II hypersensitivity reactions arise from mechanisms like complement-mediated lysis and macrophage phagocytosis.
Type III hypersensitivity involves immune complexes depositing in tissues, activating complement and attracting neutrophils to inflammatory sites.
Both systemic (e.g., serum sickness) and localized (e.g., Arthus reaction) immune complex diseases exist.
Type IV reactions are mediated by sensitized lymphocytes that kill target cells or activate other immune cells.
Allergens are specific antigens responsible for allergic reactions, predominantly of type I hypersensitivity.
Autoimmune diseases result from loss of self-antigen tolerance, often with genetic predispositions and associating with type II or type III hypersensitivity reactions.
Alloimmunity arises when the immune system reacts to antigens on tissues from the same species, as seen in transplant rejections and transfusion reactions.

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Description

Test your knowledge of infection and the body's defense mechanisms with this quiz based on Huether's Understanding Pathophysiology. Explore key points about infectious diseases, pathogens, and their impact on health. This chapter emphasizes the importance of understanding how infections influence morbidity and mortality.