Introduction to Pathogens and Immunology

Introduction to Pathogens

  • Definition of pathogens: Organisms that cause disease in a host, often without killing the host immediately, allowing the pathogen to reproduce and survive.

  • Types of pathogens:

    • Viruses

    • Bacteria

    • Fungi

    • Protists

  • Ectoparasites vs. Endoparasites:

    • Ectoparasites: External parasites like ticks and fleas which can transmit diseases by carrying pathogens.

    • Endoparasites: Live inside the host and include viruses, bacteria, and worms that can cause diseases.

Types of Pathogens and Their Impact

  • Viruses:

    • Various shapes including spherical and rod-shaped.

    • Can cause diseases such as flu and Ebola.

  • Bacteria:

    • Various shapes and can enter the body through multiple routes, causing a multitude of diseases.

  • Fungi:

    • Responsible for diseases such as athlete's foot, often underestimated until symptoms become severe.

  • Protists:

    • While fewer cases are reported, they still account for significant diseases.

Immune Defense Mechanisms

Overview of Immune Defense

  • Two lines of defense:

    1. Innate Immunity: Always present barriers.

    2. Adaptive Immunity: Activated only when a pathogen is recognized.

Innate Immunity

  • Characteristics: Non-specific defenses that act immediately to prevent infection.

  • Examples of barriers in the innate immune system:

    • Skin and mucous membranes.

    • Jaws of the respiratory tract and digestive system (e.g., stomach pH).

    • Antimicrobial secretions (e.g., sweat, tears).

The History of Immunology

  • Historical timeline:

    • Earliest evidence of immunology dates back to 430 BC.

    • Significant advancements began in the 1900s, especially post-HIV discovery in the 1980s.

    • Observations: Early methods involved using recovered individuals to care for the sick (nursing by default).

  • Variolation:

    • An ancient practice where material from disease blisters (smallpox) was used to induce immunity in healthy individuals.

    • Introduced as a formal practice around the 1400s.

    • Popularized by figures like George Washington during the Revolutionary War.

  • Edward Jenner and the development of vaccines:

    • Used cowpox to introduce immunity against smallpox (first vaccine).

    • Controversial because it involved using material from a less respected source (cowpox from peasantry) to protect against smallpox.

Development of Vaccines

  • Vaccines: Attenuated or weakened viruses used to evoke an immune response without causing disease.

  • The prefix "vaxa" in vaccine derives from Latin for cow, referencing cowpox.

  • Immunity types:

    • Innate Immunity: Built-in defenses that are always on.

    • Adaptive Immunity: Response mechanisms that activate based on specific pathogens.

Components of the Immune System

  • Immunoglobulins: Molecules crucial for immune response, including antibodies and proteins involved in the MHC (Major Histocompatibility Complex).

  • Major classifications of immunity:

    • Innate:

      • Built-in, nonspecific, rapid.

    • Adaptive:

      • Specific, memory-based, responsive to previously encountered pathogens.

Phagocytosis and Chemical Signals

  • Phagocytes: Cells that ingest and eliminate pathogens through a process called phagocytosis.

    • Steps involved:

      • Recognition of pathogens.

      • Attachment and engulfment using pseudopodia.

  • Chemotaxis: Movement of phagocytes toward chemical signals (like complement proteins) that guide them to the site of infection.

  • Inflammation: Response involving immune cells, blood vessels, and molecular mediators that help to restore tissue integrity and fight pathogens.

Summary of Innate Immunity Types

Categories of Innate Immunity

  1. Anatomical or Physical Barriers:

    • Skin, mucous membranes, eyelashes.

  2. Physiological Barriers:

    • Body temperature, pH levels, soluble factors like lysozymes and cytokines.

  3. Soluble Factors:

    • Enzymes and proteins that carry out various functions in response to pathogens (e.g., lysozymes break down cell walls).

  4. Phagocytic Barriers:

    • Cells that consume and destroy invading pathogens.

Conclusion

  • Understanding the history and mechanisms of immunity is critical to grasping how our bodies defend against pathogens.

  • The dynamic interplay between innate and adaptive immunity shapes our overall health and resistance to diseases.

  • Ongoing advancements in immunology continue to evolve our approaches to preventing and fighting infectious diseases.