Finals Study Guide: Immunology, Antimicrobial Drugs, and Pathogens in Microbiology

Immunology and HIV

Allergic Reactions

Allergic reactions are immune responses to typically harmless substances (allergens) that result in symptoms ranging from mild irritation to severe anaphylaxis.

• Anaphylaxis: A severe, life-threatening allergic reaction triggered by allergens such as insect venom, foods, or medications.

• Allergens: Substances that provoke an immune response, including pollen, dust mites, and certain foods.

• Antibodies: Immunoglobulins produced by B cells that bind to specific antigens.

• Effects: Allergic reactions can cause swelling, difficulty breathing, drop in blood pressure, and hives.

Cytotoxic Reactions

Cytotoxic reactions involve the destruction of cells by antibodies, often seen in blood transfusion incompatibilities.

• Blood Group Incompatibility: Occurs when transfused blood is not compatible with the recipient's blood type, leading to immune-mediated destruction of red blood cells.

• Rh Factor: An antigen present on red blood cells. Incompatibility between Rh-negative mother and Rh-positive fetus can cause hemolytic disease of the newborn.

Autoimmune Diseases

Autoimmune diseases occur when the immune system attacks the body's own cells and tissues.

• Examples: Lupus, rheumatoid arthritis, type I diabetes.

Grafts and Transplants

Transplantation involves moving tissue from one individual to another, with potential for immune rejection.

• Types of Grafts:

  • Autograft: Tissue from the same individual (e.g., skin graft).

  • Allograft: Tissue from a different person (most common type).

  • Xenograft: Tissue from a different species.

• Rejection: Immune response against transplanted tissue.

HIV Infection and Replication

Human Immunodeficiency Virus (HIV) targets immune cells, leading to acquired immunodeficiency syndrome (AIDS).

• HIV Structure: Enveloped RNA virus (gp120 and gp41 proteins).

• Replication Steps:

  1. Attachment: gp120 binds to CD4 receptor on host T cells.

  2. Fusion: Viral envelope fuses with host cell membrane.

  3. Reverse Transcription: Viral RNA is converted to DNA by reverse transcriptase.

  4. Integration: Viral DNA integrates into host genome.

  5. Replication: Host cell produces viral proteins.

  6. Assembly: New viruses assemble in the host cell.

  7. Release: Viruses bud off, destroying the host cell.

• Course of AIDS:

  • Acute HIV infection: Flu-like symptoms, high viral load.

  • Clinical latency: Slow virus replication, asymptomatic.

  • AIDS: Severe immunodeficiency, opportunistic infections, cancers.

Antimicrobial Drugs

Therapeutic Index and Spectrum

Antimicrobial drugs are used to treat infections by targeting specific microbial processes.

• Therapeutic Index: Ratio of toxic dose to therapeutic dose; higher index is safer.

• Spectrum:

  • Narrow Spectrum: Effective against a single group (e.g., penicillin).

  • Broad Spectrum: Effective against a wide range (e.g., tetracycline).

Mechanisms of Action

Antimicrobial drugs act by interfering with essential microbial functions.

• Cell Wall Synthesis Inhibitors: Penicillins, cephalosporins, carbapenems.

• Protein Synthesis Inhibitors: Tetracyclines, macrolides, aminoglycosides.

• Nucleic Acid Synthesis Inhibitors: Quinolones, rifampin.

• Antimetabolites: Sulfonamides, trimethoprim.

• Antiviral Drugs: Reverse transcriptase inhibitors, protease inhibitors for HIV.

Drug Resistance

Microorganisms can develop resistance to antimicrobial drugs, making treatment difficult.

• MRSA: Methicillin-resistant Staphylococcus aureus.

• VRSA: Vancomycin-resistant Staphylococcus aureus.

• Mechanisms: Enzyme production (e.g., beta-lactamase), altered target sites, efflux pumps.

Key Equations

• Therapeutic Index: $\text{Therapeutic Index} = \frac{\text{Toxic Dose}}{\text{Therapeutic Dose}}$

Pathogens and Diseases

Bacterial and Viral Diseases

Pathogens cause a variety of diseases by infecting different tissues and organs.

• Skin Infections: Staphylococcus aureus causes scalded skin syndrome; Streptococcus pyogenes causes impetigo.

• Necrotizing Fasciitis: Rapidly spreading infection by Streptococcus pyogenes.

• Heart Diseases: Endocarditis (infection of heart lining), often bacterial.

• Enterocolitis: Infection of intestines, can be bacterial or viral.

• Tetanus: Clostridium tetani toxin causes muscle rigidity.

• Botulism: Clostridium botulinum toxin causes flaccid paralysis.

• Rabies: Viral infection affecting the nervous system.

• Plague: Yersinia pestis causes bubonic, septicemic, and pneumonic forms.

• Diphtheria: Corynebacterium diphtheriae toxin causes pseudomembrane in throat.

• Dental Caries: Tooth decay caused by Streptococcus mutans.

• Staphylococcal Food Poisoning: Preformed toxins in contaminated food.

Additional Info

• Diseases can be classified by the type of pathogen (bacterial, viral, fungal, or parasitic).

• Prevention includes vaccination, hygiene, and proper food handling.

Summary Table: Types of Grafts

Type of Graft	Source	Example
Autograft	Same individual	Skin graft for burns
Allograft	Different person (same species)	Kidney transplant
Xenograft	Different species	Pig heart valve in humans