Immune System Overview

Introduction

• The immune system is crucial for defending the body against pathogens.
• Pathogens include bacteria (living cells), fungi, parasites, cancer cells, and viruses (non-living entities that replicate using host cells).
• The body uses boundaries like skin and mucous membranes to prevent pathogen entry (prevention).

Types of Immunity

1. Specific Immunity (Adaptive Immunity):

   • Learns and remembers pathogens for faster response upon re-exposure.
   • Involves memory cells, which allow for a quicker and stronger response upon second exposure to the same pathogen.
   • Vaccines function by training this system.

2. Non-Specific Immunity (Innate Immunity):

   • First line of defense; involves inflammatory response and general pathogen destruction.
   • Includes cells like neutrophils and macrophages that attack pathogens indiscriminately.
   • Triggered by tissue damage and involves vasodilation, redness, heat, swelling, and pain.

Key Components of the Immune System

• Skin and Mucous Membranes:

  • Serve as physical barriers.

• Inflammatory Response:

  • Vasodilation increases blood flow, causing redness and warmth.
  • Increased permeability allows white blood cells (neutrophils, monocytes, lymphocytes) to access the site.
  • Sometimes leads to fever to fight pathogens.

• Natural Killer Cells (NK Cells):

  • Lymphocytes that destroy tumor cells by creating pores in cell membranes.

Major Histocompatibility Complex (MHC)

• MHC proteins are crucial for immune cells to recognize self versus non-self.
• MHC presents antigen fragments on cell surfaces, signaling to immune cells whether to attack or ignore them.

Autoimmune Diseases

• Occur when the immune system fails to distinguish between self and non-self, attacking its own tissues.
• Examples include MS, rheumatoid arthritis, Graves' disease, and psoriasis.

Antigen-Presenting Cells (APCs)

• Macrophages serve as APCs linking non-specific and specific immunity.
• APCs present antigens to T cells to activate the adaptive immune response.

Cytokines

• Are signaling proteins that coordinate immune responses, often inducing fever or inflammation.
• Types include hormones, paracrine signals, and autocrine signals.

B Cells and T Cells

• B Cells: Mature in bone marrow, produce antibodies.
• T Cells: Mature in thymus, include helper, killer, and suppressor cells.
  • T Helper Cells: Coordinate immune responses by activating B cells and other T cells.
  • T Killer (Cytotoxic) Cells: Destroy infected cells directly.
  • Suppressor T Cells: Reduce immune response to prevent overactivity.

Immunological Memory

• Memory cells (B and T cells) retain information about pathogens for rapid response upon re-exposure.

Vaccination and Immunization

• Active Immunization: Through natural infection or vaccination, the body learns to fight specific pathogens.
• Passive Immunization: Involves receiving ready-made antibodies (e.g., maternal antibodies, antivenoms).

Lymphoid Organs

• Primary Lymphoid Organs: Where immune cells develop (e.g., bone marrow, thymus).
• Secondary Lymphoid Organs: Where immune responses occur (e.g., lymph nodes, spleen, tonsils).

Spleen

• Filters blood, removes old red blood cells, and mounts immune responses against blood-borne pathogens.

Peyer’s Patches

• Lymphoid tissues in the gut that monitor intestinal bacteria populations and prevent the growth of pathogenic bacteria.

Conclusion

• Understanding the immune system's components and functions is crucial for maintaining health and effectively combating infections.