Adaptive Immunity, Immunization, Immune Disorders, and Microbial Ecology: Study Guide Notes

Chapter 16: Adaptive Immunity

Five Distinctive Characteristics of Adaptive Immunity

• Specificity: Adaptive immunity targets specific antigens, distinguishing between different pathogens and even minor differences in molecular structure.

• Inducibility: Immune responses are induced only in the presence of specific antigens.

• Clonality: Once activated, lymphocytes proliferate to form clones specific to the antigen.

• Unresponsiveness to Self: Adaptive immunity typically does not target the body’s own cells due to mechanisms of self-tolerance.

• Memory: The immune system retains a memory of previously encountered antigens, resulting in a faster and stronger response upon re-exposure.

B Lymphocytes vs. T Lymphocytes

• Origin: Both originate from hematopoietic stem cells in the bone marrow.

• Differentiation: B cells mature in the bone marrow; T cells mature in the thymus.

• Functions: B cells are primarily involved in antibody-mediated (humoral) immunity, producing antibodies. T cells are involved in cell-mediated immunity, including helper, cytotoxic, and regulatory functions.

Categories of Adaptive Immunity

• Humoral Immunity: Mediated by B cells and antibodies; effective against extracellular pathogens.

• Cell-Mediated Immunity: Mediated by T cells; effective against intracellular pathogens and abnormal cells.

Antigen and Epitope

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

• Epitope: The specific part of an antigen recognized by immune cells or antibodies; also called antigenic determinant.

• Location: Epitopes are found on the surface of antigens, such as proteins, polysaccharides, or lipids.

• Difference: An antigen may have multiple epitopes, each capable of being recognized by different antibodies or T cell receptors.

Multiple Specific Antigens on Bacterial Cells

• Bacterial cells often possess multiple antigens, each with several epitopes, allowing for recognition by various immune cells.

Components of the Immune System

Cell Type	Description	Involved in Antibody- or Cell-mediated Immunity?	Location in Body
B Lymphocytes (B cells)	Produce antibodies; mature in bone marrow	Antibody-mediated (humoral) immunity	Blood, lymphoid tissues
T Lymphocytes (T cells)	Helper, cytotoxic, and regulatory functions; mature in thymus	Cell-mediated immunity	Blood, lymphoid tissues
Natural Killer (NK) Cells	Destroy infected or abnormal cells without antigen specificity	Innate immunity, but bridges to adaptive	Blood, spleen, lymph nodes

Major Histocompatibility Complexes (MHC)

• MHC I: Present on all nucleated cells; present endogenous antigens to cytotoxic T cells.

• MHC II: Present on antigen-presenting cells (APCs); present exogenous antigens to helper T cells.

Antigen-Presenting Cells (APCs)

• Include dendritic cells, macrophages, and B cells.

• Function: Process and present antigens via MHC molecules to T cells, initiating adaptive immune responses.

Phagocytic Dendritic Cells and MHC

• Dendritic cells ingest pathogens, process antigens, and present them on MHC II molecules to activate T cells.

Basic Structure of an Antibody

• Y-shaped molecule composed of two heavy chains and two light chains.

• Variable regions bind specific epitopes; constant region determines antibody class.

Roles of Antibodies in Humoral Immunity

Function	Description
Activation of Complement and Inflammation	Antibodies trigger complement cascade, enhancing pathogen destruction and inflammation.
Neutralization	Antibodies block pathogen binding sites, preventing infection.
Opsonization	Antibodies coat pathogens, enhancing phagocytosis.
Agglutination	Antibodies cross-link pathogens, forming clumps for easier removal.
Antibody-Dependent Cellular Cytotoxicity (ADCC)	Antibodies recruit NK cells to destroy antibody-coated target cells.

Types of Antibodies (Immunoglobulins)

Type	Structure	Number of Monomer Units	Location	% of Total Serum Antibodies	Special Features/Functions
IgG	Monomer	1	Blood, extracellular fluid	~80%	Crosses placenta; main antibody in secondary response
IgA	Dimer (mainly)	2	Mucosal surfaces, secretions	~10-15%	Protects mucosal areas; found in breast milk
IgM	Pentamer	5	Blood, lymph	~5-10%	First antibody produced in primary response
IgE	Monomer	1	Bound to mast cells, basophils	<1%	Involved in allergic responses, defense against parasites
IgD	Monomer	1	B cell surface	<1%	Functions mainly as B cell receptor

Cytokines

• Small proteins that mediate and regulate immunity, inflammation, and hematopoiesis.

• Examples: Interleukins, interferons, tumor necrosis factors.

Types of T Lymphocytes

• Helper T Cells (CD4+): Activate B cells, cytotoxic T cells, and macrophages.

• Cytotoxic T Cells (CD8+): Destroy infected or abnormal cells.

• Regulatory T Cells: Suppress immune responses to maintain tolerance.

Activation of Helper and Cytotoxic T Cells

• Helper T Cells: Activated by antigen presentation via MHC II on APCs; secrete cytokines to stimulate other immune cells.

• Cytotoxic T Cells: Activated by antigen presentation via MHC I; release perforin and granzymes to induce apoptosis in target cells.

Primary vs. Secondary Immune Response

• Primary Response: First exposure to antigen; slower, mainly IgM produced.

• Secondary Response: Subsequent exposures; faster and stronger, mainly IgG produced due to memory cells.

Types of Immunity

• Naturally Acquired Active: Immunity from infection.

• Naturally Acquired Passive: Maternal antibodies (e.g., breastfeeding).

• Artificially Acquired Active: Vaccination.

• Artificially Acquired Passive: Injection of antibodies (e.g., antiserum).

Breastfeeding and Immunity

• Breastfeeding provides passive immunity to infants via maternal antibodies, especially IgA.

Chapter 17: Immunization and Immune Testing

History of Immunization

• Early practices included variolation; Edward Jenner developed the first vaccine using cowpox to protect against smallpox.

Types of Vaccines

• Attenuated: Live, weakened pathogens.

• Inactivated: Killed pathogens.

• Toxoid: Inactivated toxins.

• Combination: Multiple antigens in one vaccine.

• Recombinant: Genetically engineered antigens.

Common Immunization Schedules

• CDC recommends vaccines for diseases such as measles, mumps, rubella, polio, diphtheria, tetanus, pertussis, hepatitis B, and varicella.

Herd Immunity

• Occurs when a high percentage of the population is immune, protecting those who are not immune.

Serological Tests

• Precipitation: Antigen-antibody complexes form visible precipitates.

• Agglutination: Clumping of cells or particles.

• Neutralization: Antibodies block pathogen activity.

Fluorescent Antibody Tests

• Direct: Labeled antibodies bind directly to antigen.

• Indirect: Labeled secondary antibodies detect primary antibodies bound to antigen.

Point-of-Care Testing

• Rapid diagnostic tests performed at or near the site of patient care; revolutionized infectious disease diagnosis.

Chapter 18: Immune Disorders

Allergy and Immune Disorders

• Allergy: Immune response to harmless antigens (allergens).

• Hypersensitivity: Excessive immune response.

• Immunodeficiency: Inadequate immune response.

Types of Hypersensitivity

Name	Description	Key Players
Type I (Immediate)	IgE-mediated, rapid allergic reactions	Mast cells, basophils, IgE
Type II (Cytotoxic)	Antibody-mediated cell destruction	IgG, IgM, complement
Type III (Immune Complex)	Immune complex deposition causes inflammation	IgG, IgM, complement, neutrophils
Type IV (Delayed)	T cell-mediated, delayed response	T cells, macrophages

Common Allergens and Immune Response

• Allergens can be ingested (foods), inhaled (pollen), or injected (venom).

• First exposure sensitizes; subsequent exposures trigger allergic reactions.

Histamine and Atopy

• Histamine release causes vasodilation, increased permeability, and smooth muscle contraction.

• Atopy refers to genetic predisposition to develop allergies.

Wheal and Flare Reaction

• Localized swelling (wheal) and redness (flare) at the site of allergen exposure.

Localized vs. Generalized Anaphylaxis

• Localized: Limited to one area (e.g., hay fever).

• Generalized: Systemic, potentially life-threatening (e.g., anaphylactic shock).

Autoimmune Disorders and Immune Tolerance

• Immune tolerance prevents immune response to self-antigens; breakdown leads to autoimmunity.

Organ-specific Autoimmune Disorder	Target Organs and Effects
Type I diabetes mellitus	Pancreatic beta cells destroyed; insulin deficiency
Graves disease	Thyroid gland; hyperthyroidism
Multiple sclerosis	Central nervous system; demyelination
Addison disease	Adrenal cortex; hormone deficiency

Systemic Autoimmune Disorder	Characteristics	Parts of Body Affected	Autoantibody Target
Rheumatoid arthritis	Chronic joint inflammation	Joints	Synovial membrane
Systemic lupus erythematosus (SLE)	Multi-organ inflammation	Skin, kidneys, joints, etc.	Nuclear antigens

Transplant and Graft Rejection

• Immune system may attack transplanted tissues due to recognition of foreign MHC molecules.

Primary vs. Acquired Immunodeficiency

• Primary: Genetic defects (e.g., SCID).

• Acquired: Result from infections (e.g., HIV) or treatments (e.g., chemotherapy).

Chapter 26: Microbial Ecology and Microbiomes

Microbial Ecology

• Study of interactions between microorganisms and their environment.

• Biodiversity: Variety of microbial species.

• Biomass: Total mass of microorganisms in a given environment.

Microbial Relationships

• Population: Group of the same species.

• Guild: Microbes with similar functions.

• Community: Multiple populations in an environment.

• Microbiota: Microbes in a specific habitat.

• Ecosystem: Community plus environment.

• Biofilm: Surface-associated microbial community.

Microbial Adaptation

• Competition, antagonism, and cooperation affect survival and ecological balance.

Bioremediation

• Use of microbes to degrade environmental pollutants; important for cleaning oil spills, waste treatment, etc.

Chemical Elements in Macromolecules

• Major elements: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.