Innate Immunity: Principles and Features (Chapter 11 Study Notes)

Innate Immunity: Principles and Features

Overview of the Immune System

The immune system protects the body from pathogens through two main branches: innate immunity and adaptive immunity. Both branches work together to recognize and eliminate foreign substances while distinguishing self from non-self.

• Antigens: Molecules (usually foreign) that provoke an immune response.

• Key Functions of Immunity:

  • Recognize diverse pathogens

  • Eliminate invaders once identified

  • Discriminate between self and non-self antigens

Comparison Between Innate and Adaptive Immunity

Innate and adaptive immunity differ in specificity, speed, and memory. The following table summarizes their main features:

Feature	Innate Immunity	Adaptive Immunity
Response Time	Immediate	4–7 days
Who Has It?	All eukaryotes (multicellular and unicellular)	Only vertebrates
Distinguishes Self from Non-self	Yes	Yes
Eliminates Diverse Pathogens	Yes	Yes
Remembers Pathogens	No	Yes
Tailored Response	No	Yes

• Innate Immunity: Non-specific, present from birth, responds quickly, no memory of previous pathogens.

• Adaptive Immunity: Specific, develops over time, tailored to specific pathogens, requires several days to activate, has memory for faster future responses.

Three Lines of Immune Defense

The immune system is organized into three collaborating lines of defense:

1. Innate Barrier Defenses: Physical and chemical barriers that prevent pathogen entry (e.g., skin, mucous membranes).

2. Innate Cellular and Molecular Defenses: Cells and molecules that respond to pathogens that breach barriers (e.g., phagocytes, antimicrobial peptides).

3. Adaptive Defenses: Highly specific responses involving lymphocytes (B cells and T cells) and antibodies.

Role of Normal Microbiota in Immune Responses

Normal microbiota are the collection of microbes that colonize the human body and play a central role in shaping immune responses.

• Microbiota help induce, train, and modulate immune functions.

• Changes in microbiota composition (due to antibiotics, diet, or lifestyle) can affect immune system development and function.

• Reduced diversity of microbiota is hypothesized to contribute to increased rates of allergies and autoimmune diseases.

• Experimental evidence shows that animals raised in microbe-free environments have underdeveloped immune systems.

Example: Antibiotic use can decrease microbiota diversity, potentially impacting immune responses and increasing susceptibility to certain diseases. Additional info: The "hygiene hypothesis" suggests that decreased exposure to microbes in early life may impair immune system development, leading to increased autoimmunity and allergies.