Innate and Adaptive Immunity

Definitions and Key Differences

Immunity refers to the body's ability to resist or eliminate potentially harmful foreign materials or abnormal cells. There are two main types: innate immunity and adaptive immunity.

• Innate Immunity: The non-specific, immediate defense mechanism present from birth. It does not require prior exposure to pathogens.

• Adaptive Immunity: The specific, acquired defense that develops after exposure to antigens. It involves memory and specificity.

Comparison Table:

Toll-like Receptors (TLRs)

Definition and Function

Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They recognize structurally conserved molecules derived from microbes.

• TLRs are found on the surface of immune cells such as macrophages and dendritic cells.

• They detect pathogen-associated molecular patterns (PAMPs) and activate immune cell responses.

• Example: TLR4 recognizes lipopolysaccharide (LPS) from Gram-negative bacteria.

Physical and Chemical Barriers in Innate Immunity

Role of Skin and Mucous Membranes

The skin and mucous membranes act as the first line of defense against pathogens.

• Skin: Provides a tough, impermeable barrier; secretes sebum with antimicrobial properties.

• Mucous Membranes: Line body cavities; secrete mucus to trap microbes; cilia move mucus out of the body.

Physical Factors

• Intact skin

• Mucous membranes

• Cilia in respiratory tract

• Lacrimal apparatus (tears)

• Saliva

Chemical Factors

• Lysozyme in tears, saliva, and sweat

• Low pH of skin and gastric juice

• Fatty acids in sebum

• Antimicrobial peptides

• Lactoferrin in saliva and mucus

Role of Normal Microbiota in Innate Immunity

Normal microbiota are the microorganisms that reside on and within the human body. They protect against pathogens by:

• Competing for nutrients and space

• Producing substances harmful to pathogens

• Stimulating the host's immune system

Leukocytes: Types and Functions

Classification and Roles

Leukocytes (white blood cells) are crucial for immune defense. They are classified into granulocytes and monocytes (agranulocytes).

• Granulocytes: Neutrophils, eosinophils, basophils

• Agranulocytes: Monocytes, lymphocytes

Eight Types of WBCs and Their Functions:

Phagocytes and Phagocytosis

Definition and Process

Phagocytes are cells that ingest and destroy microbes and debris. Phagocytosis is the process by which these cells engulf particles.

• Main phagocytes: Neutrophils, macrophages, dendritic cells

Steps in Phagocytosis

1. Chemotaxis: Phagocyte moves toward the site of infection in response to chemical signals.

2. Adherence: Phagocyte attaches to the microbe.

3. Ingestion: Phagocyte engulfs the microbe, forming a phagosome.

4. Digestion: Phagosome fuses with lysosome; enzymes digest the microbe.

5. Exocytosis: Waste materials are expelled from the cell.

Inflammation

Stages and Key Processes

Inflammation is a local response to injury or infection, characterized by redness, heat, swelling, and pain.

• Stages of Inflammation:

  1. Vasodilation and increased permeability of blood vessels

  2. Phagocyte migration and phagocytosis

  3. Tissue repair

• Vasodilation: Widening of blood vessels increases blood flow to the area.

• Margination: Phagocytes stick to the endothelium of blood vessels.

• Diapedesis: Phagocytes move through vessel walls to reach the site of infection.

Causes and Effects of Fever:

• Caused by pyrogens (e.g., cytokines) that reset the hypothalamic thermostat.

• Effects: Inhibits growth of pathogens, increases immune reactions, speeds up tissue repair.

The Complement System

Major Components and Consequences of Activation

The complement system is a group of proteins in blood plasma that enhance immune responses.

• Major Components: C1, C2, C3, C4, C5, C6, C7, C8, C9

• Activation occurs via three pathways: classical, alternative, lectin

Consequences of Complement Activation:

• Opsonization: Coating of pathogens to enhance phagocytosis

• Cytolysis: Formation of membrane attack complex (MAC) that lyses pathogens

• Inflammation: Attracts phagocytes and increases vascular permeability

Example Equation:

Activation of complement component C3:

Additional info: These notes expand on brief question prompts to provide a comprehensive overview suitable for exam preparation in college-level microbiology.