Innate and Adaptive Immunity, Immune Disorders, and Cardiovascular Infections: Microbiology Study Notes

Chapter 11: Innate Immunity

Overview of the Immune System and Responses

The immune system protects the body from pathogens through two main branches: innate (nonspecific) immunity and adaptive (specific) immunity. These systems work together to detect, respond to, and remember pathogens.

• Innate Immunity: Provides immediate, nonspecific defense against pathogens. Present in all eukaryotes.

• Adaptive Immunity: Develops more slowly and is specific to particular pathogens. Found only in vertebrates.

Table 11.1: Comparing Innate and Adaptive Immunity

Feature	Innate Immunity Traits	Adaptive Immunity Traits
Response time	Immediate	4–7 days
Organisms that have it	All eukaryotes (multicellular and unicellular)	Only vertebrates
Distinguishes self from foreign	Yes	Yes
Kills invaders	Yes	Yes
Effective against diverse threats	Yes	Yes
Tailors response to specific pathogens	No	Yes
Remembers antigens and amplifies response upon later exposure	No	Yes

Three Lines of Immune Defense

• Barrier defenses (innate): Physical and chemical barriers that prevent pathogen entry.

• Cellular and molecular defenses (innate): Cells and molecules that attack invaders.

• Adaptive defenses: Highly specific responses involving lymphocytes and antibodies.

First-Line Defenses: Barriers

• Mechanical Barriers: Physically remove pathogens (e.g., skin, mucous membranes, flushing by tears, saliva, urine).

• Chemical Barriers: Directly attack microbes or create hostile environments (e.g., lysozyme in tears/saliva, stomach acid, antimicrobial peptides).

• Physical Barriers: Provide a structural blockade (e.g., intact skin, mucous membranes).

Second-Line Defenses and the Lymphatic System

The lymphatic system is essential for immune surveillance and fluid balance. It includes lymph, lymphatic vessels, and lymphoid tissues.

• Lymphatic Capillaries: Collect interstitial fluid (lymph) from tissues.

• Lymph Nodes: Filter lymph and house immune cells.

• Spleen: Filters blood, removes old red blood cells, and detects pathogens.

• Mucosa-Associated Lymphoid Tissue (MALT): Protects mucosal surfaces.

Leukocytes of the Immune System

Leukocytes (white blood cells) are key players in both innate and adaptive immunity. They are classified as granulocytes or agranulocytes.

Type	Leukocyte Increased	Typical Nonimmune Causes
Neutrophils	Neutrophilia	Acute (sudden onset) bacterial infections
Eosinophils	Eosinophilia	Allergy, asthma, parasitic infection
Basophils	Basophilia	None; usually only seen with certain rare blood cancers
Monocytes	Monocytosis	Chronic infections/inflammation
Lymphocytes	Lymphocytosis (usually T & B cells)	Chronic viral infections/autoimmunity, certain cancers

• Neutrophils: Most abundant, phagocytic, first responders to infection.

• Eosinophils: Combat parasites and are involved in allergy/asthma.

• Basophils/Mast Cells: Release histamine, mediate allergic responses.

• Monocytes/Macrophages: Phagocytic, present antigens to T cells.

• Dendritic Cells: Antigen-presenting cells, bridge innate and adaptive immunity.

• Lymphocytes: B cells (produce antibodies), T cells (cell-mediated immunity), NK cells (kill infected/tumor cells).

Molecular Second-Line Defenses: Cytokines

Cytokines are signaling proteins that coordinate immune responses. They include chemokines, interleukins, interferons, and tumor necrosis factors.

Cytokine Type	Example	Notes
Chemokines	40+ types (e.g., CCL2, CXCL8)	Recruit white blood cells to sites of injury/infection
Interleukins	IL-1, IL-2 family	Regulate inflammation, stimulate immune cell development
Interferons	Type I (IFN-α, IFN-β), Type II (IFN-γ)	Antiviral effects, activate immune cells
Tumor Necrosis Factors	TNF-α	Stimulate inflammation, kill tumor cells

• Cytokine Storm: Excessive cytokine release causing tissue damage (e.g., in severe COVID-19).

Inflammation and Fever

• Inflammation: Localized response to injury/infection. Main functions:

  1. Recruit immune defenses to the site.

  2. Limit the spread of infection.

  3. Initiate tissue repair.

• Fever: Systemic increase in body temperature, enhances immune response.

Chapter 12: Adaptive Immunity

Humoral Response and Antibody Isotypes

Adaptive immunity involves highly specific responses mediated by lymphocytes. Antibodies (immunoglobulins) are produced by B cells and come in several isotypes:

Isotype	Main Features
IgG	Most abundant, crosses placenta, long-term immunity
IgM	First antibody made, effective in agglutination/complement activation
IgA	Found in secretions (mucus, milk), protects mucosal surfaces
IgE	Involved in allergy and defense against parasites
IgD	Function not well understood, found on B cells

Immunological Memory

• Primary response: First exposure to antigen, slower and less robust.

• Secondary response: Subsequent exposures, faster and stronger due to memory cells.

Active immunity results from direct exposure to antigen (infection or vaccination). Passive immunity results from receiving antibodies (maternal or therapeutic).

Types of Acquired Immunity

Type	How Acquired	Example
Naturally acquired active	Infection	Immunity after illness
Naturally acquired passive	Maternal antibodies	Antibodies crossing placenta
Artificially acquired active	Vaccination	Immunity after vaccine
Artificially acquired passive	Antiserum/antitoxin	Antivenom for snakebite

Chapter 13: Immune System Disorders

Primary and Secondary Immunodeficiencies

• Primary immunodeficiencies: Genetic, present from birth, rare.

• Secondary immunodeficiencies: Acquired due to infection, drugs, or systemic disorders (e.g., HIV/AIDS, chemotherapy, diabetes).

Table 13.1: Examples of Immunosuppressive Drugs

Drug Class	Treats	Examples
Anticonvulsants	Seizures	Carbamazepine, valproate, phenytoin
Corticosteroids	Inflammation, autoimmune disorders	Prednisone, methylprednisolone
Immunosuppressants	Transplant rejection, autoimmune disorders	Cyclosporine, azathioprine

Immune Deficiencies Caused by Infectious Agents

• HIV: Infects T helper cells, leading to AIDS.

• Other agents: Human T cell lymphotropic viruses, Epstein-Barr virus, measles virus.

Autoimmune Disorders

Autoimmune diseases occur when the immune system attacks self-tissues. Over 100 types exist, affecting various organs (e.g., type 1 diabetes, multiple sclerosis, rheumatoid arthritis).

Table 13.2: Some Autoimmune Disorders with Possible Infectious Agent Association

Disease	Features	Implicated Infectious Agents
Type 1 diabetes	Immune system attacks insulin-producing cells	Coxsackievirus B
Guillain-Barré syndrome	Peripheral nerves attacked	Campylobacter jejuni
Rheumatic heart disease	Heart inflammation after strep infection	Streptococcus pyogenes
Multiple sclerosis	Loss of myelin sheath in CNS	EBV, other viruses

Hypersensitivity Reactions

Hypersensitivity is an exaggerated immune response causing tissue damage. There are four types:

Type	Mechanism	Examples
I (Immediate/IgE-mediated)	IgE binds mast cells, releases histamine	Allergies, asthma, anaphylaxis
II (Cytotoxic)	IgG/IgM bind cells, activate complement	Hemolytic anemia, transfusion reactions
III (Immune complex-mediated)	Antigen-antibody complexes deposit in tissues	Serum sickness, lupus
IV (Delayed/cell-mediated)	T cells mediate response	Contact dermatitis, TB skin test

Type I Hypersensitivity (Allergy)

• IgE-mediated, rapid onset (minutes).

• Common triggers: pollen, food, drugs, insect stings.

• Symptoms: hives, asthma, anaphylaxis.

Table 13.4: Type I Hypersensitivities: Signs and Symptoms

Type I Category	Signs/Symptoms
Food/drug allergies	Hives, swelling, nausea, vomiting, diarrhea, anaphylaxis
Atopic asthma	Cough, shortness of breath
Seasonal allergies	Congestion, sneezing, itchy eyes
Atopic dermatitis	Dry, scaly skin rash

Diagnosing Allergies

• Blood tests: Measure IgE titers to allergens.

• Skin tests: Quick, but may cause local reactions (wheal and flare).

Type II Hypersensitivity (Cytotoxic)

• IgG/IgM antibodies target cells, leading to cell destruction.

• Examples: Hemolytic disease of the newborn, transfusion reactions.

Type III Hypersensitivity (Immune Complex)

• Immune complexes deposit in tissues, causing inflammation.

• Examples: Serum sickness, lupus, rheumatoid arthritis.

Type IV Hypersensitivity (Delayed, Cell-Mediated)

• Mediated by T cells, not antibodies.

• Examples: Contact dermatitis, tuberculin skin test, autoimmune diseases (e.g., Hashimoto's thyroiditis, type 1 diabetes).

Tuberculin Skin Test (PPD Test)

• Detects exposure to Mycobacterium tuberculosis.

• PPD injected into forearm; induration measured after 48–72 hours.

Anaphylaxis

• Localized: Limited to one area (e.g., hives, asthma).

• Systemic: Life-threatening, involves multiple organ systems, requires immediate treatment (e.g., epinephrine).

Blood Groups and Transfusion Compatibility

Blood types are determined by antigens on red blood cells (A, B, AB, O, and Rh factor). Compatibility is crucial to prevent transfusion reactions.

Blood Type	Antigen(s) Present	Antigen(s) Missing	Can Receive From
AB+	A, B, Rh	None	All types (universal recipient)
O-	None	A, B, Rh	O- only (universal donor)
A+	A, Rh	B	A+, A-, O+, O-
B+	B, Rh	A	B+, B-, O+, O-
AB-	A, B	Rh	AB-, A-, B-, O-
O+	Rh	A, B	O+, O-

• Hemolytic disease of the newborn (HDN): Occurs when Rh- mother carries Rh+ fetus; maternal antibodies attack fetal red cells.

Chapter 14: Vaccines

Purpose and Mechanism of Vaccines

• Vaccines stimulate adaptive immunity, leading to immunological memory.

• Herd immunity protects unvaccinated individuals when a high percentage of the population is immune.

Types of Vaccines

Type	Composition	Advantages	Disadvantages
Live attenuated	Weakened pathogens	Strong, long-lasting immunity	Risk in immunocompromised
Inactivated	Killed pathogens	Safe, stable	Weaker, may need boosters
Subunit/conjugate	Parts of pathogens	Few side effects	May need boosters

Chapter 21: Cardiovascular & Lymphatic Infections

Cardiovascular System Structure and Function

• The heart pumps blood through arteries, veins, and capillaries.

• Lymphatic vessels collect interstitial fluid and return it to the bloodstream.

Sepsis and Septic Shock

• Sepsis: Life-threatening organ dysfunction due to dysregulated immune response to infection.

• Septic shock: Severe sepsis with dangerously low blood pressure and organ failure.

Systemic Infections

Many pathogens can cause systemic infections affecting the cardiovascular and lymphatic systems. Examples include:

Infection	Agent	Systemic Considerations
Chikungunya	Virus	Arthralgia, fever, rash
Malaria	Plasmodium spp.	Fever, anemia, organ damage
Histoplasmosis	Fungus	Pulmonary and systemic symptoms

Disease Snapshots

• Zika Virus: Flavivirus, transmitted by mosquitoes, can cause birth defects (microcephaly).

• Mononucleosis: Caused by Epstein-Barr virus, leads to fever, sore throat, lymphadenopathy.

Additional info: These notes expand on the provided material with definitions, tables, and examples for clarity and completeness.