Unit 4 Review: Immunity and Immune Responses

Unit 4 Review: Immunity and Immune Responses

Overview

This unit covers the immune system, focusing on the lines of defense, types of immunity, and the cells and molecules involved in immune responses. The material is relevant to the following microbiology chapters: Innate Immunity (Ch. 17), Adaptive Immunity (Ch. 18), and Applications of the Immune Response (Ch. 20).

Innate Immunity

First Line of Defense

The first line of defense consists of anatomical and physiological barriers that prevent pathogens from entering the body.

• Specificity: The first line of defense is nonspecific, meaning it targets a broad range of pathogens rather than specific ones.

• Anatomical Defenses: Includes skin, mucous membranes, and secretions (e.g., tears, saliva, mucus).

• Types of Harm: These barriers block entry, trap pathogens, and contain antimicrobial substances.

Second Line of Defense

The second line of defense is also nonspecific and involves internal mechanisms that respond to pathogens that breach the first line.

• Components: Includes phagocytic cells (e.g., neutrophils, macrophages), inflammation, fever, and antimicrobial proteins.

• Blood Cells: White blood cells (leukocytes) play a key role. Types include neutrophils, eosinophils, basophils, monocytes, and lymphocytes.

• Inflammation: A localized response to infection or injury characterized by redness, heat, swelling, and pain. It helps contain and eliminate pathogens.

• Fever: An increase in body temperature that can inhibit pathogen growth and enhance immune cell activity.

• Phagocytosis: The process by which phagocytes engulf and digest pathogens. Steps include chemotaxis, adherence, ingestion, digestion, and exocytosis.

Interferons

Interferons are proteins produced by virus-infected cells that help protect neighboring cells from viral infection.

• Function: Interferons interfere with viral replication and activate immune cells.

Adaptive Immunity

Third Line of Defense

The third line of defense is specific and involves the adaptive immune response, which targets specific pathogens.

• Key Characteristics: Specificity, memory, and ability to distinguish self from non-self.

• Cells Involved: Lymphocytes (B cells and T cells).

• Antigens: Substances that provoke an immune response; usually proteins or polysaccharides on the surface of pathogens.

• Antibodies: Proteins produced by B cells that bind to specific antigens and neutralize or mark them for destruction.

Major Histocompatibility Complex (MHC)

MHC molecules are cell surface proteins essential for the recognition of self and presentation of antigens to T cells.

• MHC I: Found on all nucleated cells; presents endogenous antigens to cytotoxic T cells.

• MHC II: Found on antigen-presenting cells; presents exogenous antigens to helper T cells.

Types of Immunity

Immunity can be classified based on how it is acquired:

Type of Immunity	How Acquired	Example
Active Natural Immunity	Exposure to pathogen	Recovery from infection
Active Artificial Immunity	Vaccination	Immunization with vaccine
Passive Natural Immunity	Transfer from mother	Antibodies via placenta or colostrum
Passive Artificial Immunity	Injection of antibodies	Antiserum administration

Cells of the Immune System

Key Cell Types

• Plasma Cells: Differentiated B cells that produce antibodies.

• Memory Cells: Long-lived cells that provide rapid response upon re-exposure to the same antigen.

• Cytotoxic (Killer) T Cells: Destroy infected or abnormal cells by recognizing antigens presented by MHC I.

• Helper T Cells: Activate B cells and cytotoxic T cells; recognize antigens presented by MHC II.

• Suppressor (Regulatory) T Cells: Modulate immune response to prevent overactivity.

Functions and Matching

Cell Type	Function
Plasma Cells	Produce antibodies
Memory Cells	Enable faster, stronger response upon re-exposure
Cytotoxic T Cells	Attack and lyse infected or abnormal cells
Helper T Cells	Activate B cells and cytotoxic T cells
Suppressor T Cells	Regulate and suppress immune response

Applications of the Immune Response

Vaccination

• Purpose: To induce active artificial immunity by exposing the immune system to antigens without causing disease.

• Types: Live attenuated, inactivated, subunit, and toxoid vaccines.

Immunotherapy

• Passive Immunotherapy: Administration of pre-formed antibodies for immediate protection.

• Active Immunotherapy: Stimulation of the patient's own immune system to fight disease.

Key Terms and Definitions

• Antigen: Any substance that can induce an immune response.

• Antibody: A protein produced by B cells that binds to a specific antigen.

• Phagocytosis: The process by which cells engulf and digest particles.

• Immunity: The ability to resist infection or disease.

Important Equations

• Antibody-Antigen Binding:

$\text{Ag} + \text{Ab} \rightarrow \text{Ag-Ab complex}$

• Rate of Immune Response:

$\text{Rate} = k[\text{Antigen}][\text{Lymphocyte}]$

Summary Table: Types of Immunity

Immunity Type	Source	Duration	Example
Active Natural	Infection	Long-term	Recovery from measles
Active Artificial	Vaccination	Long-term	MMR vaccine
Passive Natural	Maternal antibodies	Short-term	Antibodies in breast milk
Passive Artificial	Injected antibodies	Short-term	Antiserum for rabies

Additional info: Academic context and definitions have been expanded for clarity and completeness. Tables have been inferred and reconstructed for study purposes.