Disorders Associated With The Immune System#4

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Hypersensitivity States

Definitions and Types of Hypersensitivity

Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions are classified based on the immune mechanism and time of onset.

Hypersensitivity: An exaggerated or inappropriate immune response to an antigen.
Allergen: A substance that causes an allergic reaction.

Types of Hypersensitivity

Type I – Anaphylactic Reaction: Immediate, IgE-mediated; includes allergies and systemic anaphylaxis.
Type II – Cytotoxic Reaction: Antibody-mediated destruction of cells (e.g., transfusion reactions).
Type III – Immune Complex Reaction: Deposition of antigen-antibody complexes causing inflammation (e.g., post-streptococcal glomerulonephritis).
Type IV – Cell-Mediated Reaction: Delayed, T-cell mediated (e.g., contact dermatitis, graft rejection).

Key Features and Examples

Localized vs. Systemic Anaphylaxis: Localized affects a specific area (e.g., hay fever); systemic involves the whole body and can be life-threatening.
Desensitization: Gradual exposure to increasing doses of allergen to reduce sensitivity.
Transfusion Reactions: Example of Type II hypersensitivity; antibodies attack transfused blood cells.
Graft Rejection: Example of Type IV hypersensitivity; T cells attack transplanted tissue.
Autoimmune Diseases: Multiple sclerosis (Type IV), Graves' disease (Type V).

Diagnostic and Clinical Applications

Mantoux Test: Used for tuberculosis diagnosis; positive result indicates Type IV hypersensitivity.
Post-streptococcal Glomerulonephritis: Type III reaction; immune complexes deposit in kidneys.

HIV/AIDS

Structure, Replication, and Diagnosis

Human Immunodeficiency Virus (HIV) is a retrovirus that attacks CD4+ T cells, leading to Acquired Immunodeficiency Syndrome (AIDS).

Virus Structure: Enveloped RNA virus with reverse transcriptase.
Replication Cycle: Attachment, fusion, reverse transcription, integration, assembly, and budding.
Latent vs. Clinical AIDS: Latent phase: low viral load, high CD4+ count; AIDS: high viral load, low CD4+ count, opportunistic infections.
Seroconversion: Development of detectable antibodies against HIV.
Transmission: Blood, sexual contact, vertical (mother to child).
Diagnostic Tests: ELISA (screening), Western blot (confirmation), PCR (viral load); ELISA is most sensitive post-infection.

Vaccines

Types and Mechanisms

Vaccines stimulate the immune system to develop protection against infectious diseases.

Whole Agent Vaccines: Contain entire pathogen (attenuated or inactivated).
Subunit Vaccines: Contain parts of the pathogen (toxoid, acellular, recombinant, DNA/mRNA).

Type	Example	Mechanism
Toxoid	Tetanus toxoid	Inactivated toxin
Acellular	Pertussis	Purified components
Recombinant	Hepatitis B	Genetically engineered proteins
DNA/mRNA	COVID-19 vaccines	Genetic material encoding antigen

Advantages and Disadvantages

Attenuated: Strong, long-lasting immunity; risk in immunocompromised.
Inactivated: Safer, but may require boosters.

Antibody Function and ELISA

Agllutination: Antibodies cause clumping of antigens; used to determine antibody titer.
ELISA: Enzyme-linked immunosorbent assay; detects antigen or antibody using enzyme-labeled antibodies.
Sandwich ELISA: Captures antigen between two antibodies.
Indirect ELISA: Detects antibodies in patient serum.

Control of Microbial Growth

Definitions and Methods

Microbial control involves reducing or eliminating microorganisms to prevent infection and contamination.

Sterilization: Complete destruction of all microorganisms.
Disinfection: Elimination of most pathogens (not spores).
Antisepsis: Disinfection of living tissue.
Degerming: Removal of microbes from a limited area.
Bacteriostatic: Inhibits growth.
Bactericidal: Kills bacteria.
Sepsis: Presence of pathogens in tissue.
Asepsis: Absence of pathogens.

Moist Heat Methods

Method	Effectiveness	Sterilizing?
Boiling	Kills most pathogens	No
Autoclaving	Kills all microbes, spores	Yes
Pasteurization	Reduces pathogens	No

Thermal Death Terms

Thermal Death Point: Lowest temperature at which all microbes are killed in 10 minutes.
Thermal Death Time: Minimum time to kill all microbes at a given temperature.

Types of Pasteurization

Historic: Traditional, lower temperature, longer time.
High-temperature, short-time (HTST): Modern, higher temperature, shorter time.

Disinfectants and Resistance

Types: Phenols, bisphenols, alcohols, halogens, oxidizing agents, surfactants, heavy metals, aldehydes, gaseous agents.
Microbial Resistance: Prions > Endospores > Mycobacteria > Gram-negative bacteria > Gram-positive bacteria > Viruses

Antimicrobial Drugs

Definitions and Classifications

Antimicrobial drugs are chemicals that inhibit or kill microorganisms. They are classified by spectrum and mechanism.

Antibiotic: Substance produced by microorganisms that inhibits others.
Spectrum of Activity: Range of organisms affected (broad vs. narrow).

Mechanisms of Action

Inhibitors of Cell Wall Synthesis: Penicillins, cephalosporins.
Inhibitors of Protein Synthesis: Tetracyclines, aminoglycosides.
Inhibitors of Nucleic Acid Synthesis: Quinolones, rifampin.
Inhibitors of Essential Metabolic Pathways: Sulfonamides.

Drug Resistance Mechanisms

Decreased permeability
Activation of drug pumps
Change in drug binding site
Use of alternate metabolic pathway

Antifungal, Antiprotozoan, and Antiviral Drugs

Drug	Target Organism	Mechanism
Ketoconazole	Fungi	Inhibits ergosterol synthesis
Metronidazole	Protozoa	DNA damage
Quinine derivatives	Protozoa (malaria)	Inhibits heme detoxification
Acyclovir	Herpesvirus	Inhibits viral DNA polymerase
AZT (Zidovudine)	HIV	Reverse transcriptase inhibitor

Clavulanic Acid

Function: Inhibits beta-lactamase, allowing penicillins to remain effective.

Biotechnology and Recombinant DNA

Restriction Enzymes and Vectors

Restriction Endonucleases: Enzymes that cut DNA at specific sequences.
T4 Ligase: Enzyme that joins DNA fragments.
Vectors: DNA molecules used to transfer genetic material (plasmids, viruses).

Transformation Procedures

Chemical Transformation: Use of chemicals to induce uptake of DNA.
Electroporation: Use of electric pulse to introduce DNA.

Polymerase Chain Reaction (PCR)

Function: Amplifies specific DNA sequences for diagnostics and research.
Key Components:
- Taq DNA polymerase
- ssDNA primers
- Denaturation step

Environmental and Applied Microbiology

Nitrogen Cycle and Waste Treatment

Ammonification: Conversion of organic nitrogen to ammonia.
Nitrification: Conversion of ammonia to nitrite/nitrate.
Denitrification: Conversion of nitrate to nitrogen gas.
Nitrogen Fixation: Conversion of atmospheric nitrogen to ammonia.

Sewage Treatment

Primary Treatment: Removal of solids.
Secondary Treatment: Biological degradation of organic matter.
Disinfection: Elimination of pathogens.

Microorganisms as Weapons

Anthrax, Plague, and Smallpox

Bacillus anthracis: Gram-positive, spore-forming bacterium; causes anthrax (cutaneous, gastrointestinal, inhalation).
Yersinia pestis: Gram-negative bacterium; causes plague (bubonic, pneumonic).
Variola virus: Causes smallpox; transmitted via respiratory droplets.

Advantages and Disadvantages of Bioweapons

Advantages: High infectivity, potential for mass casualties.
Disadvantages: Unpredictable spread, ethical concerns, risk to handlers.

Vaccination and Disease Progression

Vaccinia Virus: Used in smallpox vaccine; provides immunity.
Disease Progression: Incubation period, major signs, fatality rates.

Transmission and Control

Transmission: Direct contact, respiratory droplets, vectors (for plague).
Control: Vaccination, quarantine, antibiotics (for bacterial agents).

Additional info: These notes expand on the brief question prompts by providing definitions, mechanisms, and examples for each major topic, ensuring a self-contained study guide suitable for exam preparation in a college-level Microbiology course.