Overview of the Immune System

Function and Organization

The immune system is essential for protecting the body from disease-causing organisms known as pathogens. It is organized into two main branches that work together to defend the body:

• Innate Immune System

• Adaptive Immune System

Pathogens are organisms (such as bacteria, viruses, fungi, and parasites) that cause disease. The immune system's primary function is to identify and eliminate these threats.

Innate Immunity

Characteristics of Innate Immunity

Innate immunity is the body's first line of defense and is considered nonspecific immunity because it treats all pathogens in the same way. Key features include:

• No specific molecular recognition – does not distinguish between different pathogens.

• No memory – does not remember previous infections.

• Always present and active – provides constant protection.

• Contains and destroys most pathogens – helps maintain health by preventing infection.

Components of Innate Immunity

• Surface Barriers

  • Skin

  • Mucous membranes

• Internal Defenses

  • Phagocytes

  • Natural killer cells

  • Inflammation

  • Antimicrobial proteins

  • Fever

Tools of Innate Immunity

• Barriers

  • Skin – acts as a physical barrier to pathogens.

  • Mucous membranes – trap and help remove microbes.

• Cells

  • Phagocytes – cells that ingest and destroy pathogens.

  • Natural killer cells – destroy infected or abnormal cells.

• Antimicrobial Proteins – proteins that inhibit or destroy microbes.

• Fever – elevated body temperature that can inhibit pathogen growth.

Adaptive Immunity

Characteristics of Adaptive Immunity

Adaptive immunity is a highly specialized defense system that targets specific pathogens. It is also known as specific immunity and has the following features:

• Specific molecular recognition – can identify and target particular pathogens.

• Memory – remembers previous encounters with pathogens for faster future responses.

• Delayed response – takes several days to become fully active, usually after innate immunity is breached.

• More powerful – can eliminate pathogens that evade innate defenses.

Components of Adaptive Immunity

• Humoral Immunity – mediated by B cells and antibodies, targets extracellular pathogens.

• Cellular Immunity – mediated by T cells, targets intracellular pathogens and abnormal cells.

Tools of Adaptive Immunity

• Cells

  • Lymphocytes

    • B cells – produce antibodies.

    • T cells – regulate immune responses and kill infected cells.

• Proteins

  • Antibodies – proteins that specifically bind to antigens on pathogens.

Comparison Table: Innate vs Adaptive Immunity

Example of Cooperation

• When a pathogen breaches the skin (innate barrier), phagocytes (innate cells) may ingest it. If the pathogen persists, adaptive immunity is activated, with B cells producing antibodies and T cells targeting infected cells.

Additional info: The immune system's two branches are interdependent, with innate immunity providing immediate defense and adaptive immunity offering targeted, long-lasting protection. Both are essential for maintaining health and preventing disease.