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Immune Immunity: Nonspecific Defenses of the Host

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Immune Immunity: Nonspecific Defenses of the Host

Overview

This section introduces the fundamental concepts of the host's nonspecific (innate) immune defenses, focusing on the physical, chemical, and cellular mechanisms that protect the body from infection. The following study notes are organized according to the provided learning objectives, expanding on each with definitions, examples, and academic context.

16-1 Innate vs. Adaptive Immunity

Innate immunity refers to the host defenses that are present at birth and provide rapid, nonspecific protection against pathogens. Adaptive immunity develops more slowly and provides specific, long-lasting protection through the action of lymphocytes and the production of antibodies.

  • Innate Immunity: Immediate, non-specific, no memory. Includes barriers (skin, mucous membranes), phagocytes, inflammation, fever, and antimicrobial substances.

  • Adaptive Immunity: Specific, slower to develop, has memory. Involves B cells (antibody production) and T cells (cell-mediated responses).

  • Example: The skin preventing entry of bacteria (innate) vs. antibody production after vaccination (adaptive).

16-2 Role of Skin and Mucous Membranes in Innate Immunity

The skin and mucous membranes act as the first line of defense by providing physical and chemical barriers to infection.

  • Skin: Tightly packed epithelial cells, keratinized surface, and dryness inhibit microbial growth.

  • Mucous Membranes: Line the respiratory, gastrointestinal, and genitourinary tracts; secrete mucus to trap microbes.

  • Example: Cilia in the respiratory tract move trapped particles out of the lungs.

16-3 Physical vs. Chemical Factors in Innate Immunity

Physical and chemical factors work together to prevent pathogen entry and survival.

  • Physical Factors: Barriers that physically block or remove microbes.

  • Chemical Factors: Substances that inhibit or destroy microbes.

Examples of Physical Factors:

  • Intact skin

  • Mucus and ciliary escalator

  • Lacrimal apparatus (tears)

  • Saliva

  • Urine flow

Examples of Chemical Factors:

  • Lysozyme in tears, saliva, and sweat

  • Low pH of gastric juice

  • Fatty acids in sebum

  • Antimicrobial peptides (defensins)

  • Transferrins in blood (bind iron)

16-4 Role of Normal Microbiota in Innate Immunity

Normal microbiota are the microorganisms that colonize the body without causing disease. They protect the host by:

  • Competing with pathogens for nutrients and space

  • Producing substances harmful to pathogens (bacteriocins)

  • Stimulating the host's immune system

  • Example: Lactobacillus in the vagina lowers pH, inhibiting pathogen growth.

16-5 Classification and Roles of Leukocytes

Leukocytes (white blood cells) are classified as granulocytes or agranulocytes based on the presence of granules in their cytoplasm.

  • Granulocytes: Neutrophils, eosinophils, basophils

  • Agranulocytes: Monocytes, lymphocytes

  • Roles: Granulocytes are involved in phagocytosis, inflammation, and allergic responses; monocytes differentiate into macrophages and dendritic cells for phagocytosis and antigen presentation.

16-6 Types and Functions of White Blood Cells

White blood cells have specialized functions in immune defense.

Type

Main Function

Neutrophils

Phagocytosis of bacteria and fungi

Basophils

Release histamine in allergic responses

Eosinophils

Combat parasites; involved in allergic reactions

Monocytes

Differentiate into macrophages for phagocytosis

Lymphocytes

B cells (antibody production), T cells (cell-mediated immunity), NK cells (kill infected cells)

16-7 Lymphatic vs. Blood Circulatory Systems

The lymphatic system and blood circulatory system are interconnected but have distinct roles in immunity.

  • Blood Circulatory System: Transports oxygen, nutrients, and immune cells throughout the body.

  • Lymphatic System: Drains excess fluid from tissues, filters lymph through lymph nodes, and facilitates immune cell activation.

  • Comparison: Lymphatic vessels are one-way (toward the heart), while blood vessels form a closed loop.

16-8 Phagocytes and Phagocytosis

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: Chemotaxis, adherence, ingestion, digestion, exocytosis

  • Example: Macrophages engulfing bacteria in infected tissue.

16-9 Process and Stages of Phagocytosis

The process of phagocytosis involves several key stages:

  1. Chemotaxis: Phagocyte moves toward chemical signals from microbes or damaged cells.

  2. Adherence: Phagocyte attaches to the microbe.

  3. Ingestion: Microbe is engulfed into a phagosome.

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

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

16-10 Stages of Inflammation

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

  • Stages:

    1. Vasodilation and increased permeability of blood vessels

    2. Phagocyte migration and phagocytosis

    3. Tissue repair

  • Purpose: To contain infection, remove debris, and initiate healing.

16-12 Cause and Effects of Fever

Fever is an abnormally high body temperature, often in response to infection.

  • Cause: Pyrogens (e.g., bacterial toxins, cytokines) reset the hypothalamic thermostat.

  • Effects: Inhibits growth of some microbes, increases immune cell activity, and speeds up tissue repair.

  • Equation:

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