Immune Disorders Flashcards

Fundamentals of Immunity and Functions of the Immune System

Primary Functions of the Immune System:
- Protection: Defends the body against foreign pathogens, microorganisms, and toxic substances.
- Maintenance of Homeostasis: Clears cellular debris, damaged cells, and maintains internal physiological balance.
- Surveillance: Continuously monitors host tissues to identify and destroy mutated, malignant, or foreign cells.
- Self vs. Foreign Discrimination: Ability to distinguish host tissues ("self") from exogenous invaders ("foreign").
Inappropriate Immune Responses:
- Hyperreactivity: An exaggerated, inappropriate immune response to harmless external substances (e.g., allergic reactions, hypersensitivities).
- Inability to Distinguish Self: Failure of immunological tolerance, leading the immune system to launch an attack against host tissues (autoimmunity).

White Blood Cells: Lymphocytes

Illustration comparing B-cells and T-cells

T Cells (T Lymphocytes):
- Immune Response Type: Mediate the cell-mediated response.
- Organ Site: Maturation takes place in the thymus.
- Functional Role: Maintain constant, ongoing surveillance throughout the body. Directly attack infected host cells, intracellular pathogens, and abnormal cells.
- Cellular Cooperation: Helper T cells stimulate B cells to produce specific antibodies.
B Cells (B Lymphocytes):
- Immune Response Type: Mediate the humoral response.
- Organ Site: Reside and function primarily within lymph nodes and peripheral lymphoid tissues.
- Functional Role: Attack invaders and extracellular pathogens present outside the body's cells.
- Memory Formation: Form memory cells following an initial antigen exposure to confer long-term adaptive protection.

Classifications and Acquisition of Immunity

Naturally Acquired Immunity: Innate (Nonspecific):
- Serves as the body's first line of defense.
- Consists of non-specific physical and chemical barriers that protect the host from the external environment.
- Physical and Chemical Barrier Examples:
  - Skin and Mucus Membranes: Intact epithelial tissue preventing entry of microorganisms.
  - Stomach Acid: Highly acidic environment that neutralizes ingested pathogens.
  - Sebaceous Glands and Secretions: Cutaneous lipid secretions with antimicrobial properties.
  - Normal Flora: Commensal organisms that outcompete potential pathogens.
Artificially Acquired and Adaptive Immunity: Active:
- Serves as the second line of defense.
- Produces a highly specific immunologic reaction to invading antigens and establishes immunological memory.
- Key Immune System Organs Involved:
  - Thymus
  - Spleen
  - Bone marrow
  - Lymphatic system / Lymph nodes
Active Immunity vs. Passive Immunity:
- Active Immunity (Long-Term Protection):
  - Mechanism: The host's own immune system produces specific antibodies in response to antigen exposure.
  - Triggers: Triggered naturally by clinical or subclinical infection, or artificially through vaccination.
  - Duration: Long-lasting defense that provides immunity for many years or across an entire lifetime.
- Passive Immunity (Immediate Protection):
  - Mechanism: The host receives preformed, borrowed antibodies synthesized in another organism.
  - Acquisition: Transferred naturally from mother to fetus/infant (transplacental or via breast milk) or artificially via antibody-containing blood products (e.g., immune globulin infusions).
  - Duration: Fast-acting immediate protection that is temporary, lasting only for a period of weeks to months.

Hypersensitivity Reactions

Skin manifestation of immediate hypersensitivity hives and rash

Immediate Hypersensitivity:
- Etiology: Underlying genetic predisposition/defect leading to excessive production of Immunoglobulin E ( $IgE$ ).
- Clinical Cues: Presentation of acute symptoms triggered by rapid histamine release upon antigen re-exposure (urticaria, skin rash, localized edema).
- Management Strategies:
  - Trigger Avoidance: Strict avoidance of identified allergens.
  - Pharmacotherapy: Antihistamine administration to block $H_1$ receptors.
  - Immunotherapy: Desensitization protocols to modify the IgE-mediated antibody response over time.

Poison ivy plant illustrating delayed hypersensitivity

Delayed Hypersensitivity:
- Mechanism: T cell-mediated immune reaction where inflammatory symptoms manifest $24\text{ to }72\text{ hours}$ following antigen exposure.
- Clinical Examples:
  - Contact dermatitis (e.g., exposure to poison ivy / urushiol).
  - Blood transfusion reactions (delayed hemolytic responses).
  - Tissue graft and organ transplant rejections.

Anaphylaxis and Emergency Management

Anaphylactic reaction symptoms including angioedema

Pathophysiology: A life-threatening, severe systemic overreaction/hypersensitivity reaction to an environmental or pharmacologic allergen.
Clinical Cues and Manifestations:
- Respiratory Distress: Upper airway obstruction leading to inspiratory stridor, wheezing, and dyspnea.
- Hemodynamic Instability: Severe tachycardia and rapid drop in blood pressure (hypotension), progressing to anaphylactic shock.
- Cutaneous / Mucosal Cues: Cyanosis, pallor, urticaria, and severe angioedema (swelling of facial structures, lips, tongue, and pharynx).
Medical and Nursing Management Protocol:
- Airway: Establish and maintain patency of the patient's airway immediately.
- Breathing: Administer supplemental oxygen.
- Circulation: Secure immediate intravenous (IV) vascular access for rapid fluid resuscitation and drug delivery.
- Oral Intake: Maintain strict NPO (nothing by mouth) status.
- Emergency Pharmacotherapy:
  - Epinephrine (EPI): Primary first-line medication for systemic vasoconstriction and bronchodilation.
  - Antihistamines: Secondary intervention to block continued histamine binding.
  - Inhaled Medications: Inhaled bronchodilators to treat persistent bronchospasm.
- Prevention: Identification of triggers and education on complete avoidance.

Immunodeficiency Disorders

Weakened immune system concept illustration

Primary Immunodeficiency:
- Congenital or inherited genetic defects present at birth.
- Characterized by deficient or malfunctioning phagocytes, B cell deficiencies, or T cell deficiencies.
Secondary Immunodeficiency:
- Acquired immunodeficiency resulting from external non-genetic factors.
- Causes include therapeutic immunosuppression (e.g., chemotherapy, systemic corticosteroids), severe malnutrition, radiation, chronic diseases, or viral infections (e.g., HIV).

Autoimmune Disorders

Common autoimmune diseases diagram

Pathophysiology: Breakdown of immune tolerance resulting in an inability to distinguish self-antigens from foreign antigens; the immune system generates autoantibodies that target and attack the host's own tissues.
Most Common Autoimmune Diseases:
- Systemic Lupus Erythematosus (Lupus)
- Rheumatoid Arthritis
- Crohn's Disease
- Multiple Sclerosis (MS)
- Hashimoto's Thyroiditis
- Graves' Disease
- Psoriasis
- Type $1$ Diabetes Mellitus
Medical Management:
- Immunosuppressant Agents: Primary drug class used to quiet the host immune response.
- Corticosteroids: Essential cornerstone intervention to suppress acute inflammatory and autoimmune cascades.
- Biologics / DMARDs: Targeted biologic therapies and Disease-Modifying Antirheumatic Drugs to halt progressive tissue damage.

Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS)

Flowchart of HIV progression to AIDS

Definitions and Characteristics:
- Human Immunodeficiency Virus (HIV): Retrovirus that infects and progressively destroys immune cells. Infected individuals can remain asymptomatic for many years while remaining infectious and capable of transmitting the virus.
- Acquired Immunodeficiency Syndrome (AIDS): The terminal stage of HIV infection characterized by profound immunocompromise and total breakdown of cell-mediated immunity.
Transmission and Risk Factors:
- Transmitted through direct exposure to infected body fluids (blood, semen, vaginal secretions, and breast milk).
Pathophysiology of HIV Progression:

HIV binding to CD4 receptor and coreceptor via gp120

1.  HIV viral particles utilize surface glycoprotein  $gp120$  to bind specifically to the  $CD4$  receptor and coreceptor on host helper T cells.
2.  The viral envelope fuses with the helper T cell membrane, injecting viral genetic material.
3.  The immune system mounts an initial counter-response, keeping viral multiplication temporarily in check, but helper T cells continue to be invaded.
4.  Over time, viral replication rates accelerate and overcome the helper T cell population.
5.  Clinical progression varies individually based on viral load metrics.
6.  Cytotoxic (killer) T cells eventually recognize and destroy infected helper T cells, further reducing total CD4 count.
7.  The immune system becomes severely suppressed.
8.  Full-blown AIDS develops.

Diagnostic Laboratory Metrics ( $CD4^+$ T-Cell Thresholds):
- Normal $CD4^+$ Count: Ranges from $500\text{ to }1500\,\text{cells}/\mu\text{L}$ .
- AIDS Diagnosis Threshold: Defined as a $CD4^+$ count dropping below $200\,\text{cells}/\mu\text{L}$ (or the presence of AIDS-defining clinical conditions).

Kaposi sarcoma cutaneous lesion on nose

Clinical Stages and Presentations:
- Acute Retroviral Syndrome: Early symptomatic infection presenting with flu-like symptoms, fever, lymphadenopathy, and generalized cutaneous rash.
- Opportunistic Infections and Atypical Cancers: As immunodeficiency deepens, patients develop severe opportunistic infections and atypical malignancies (such as Kaposi sarcoma, shown above as red/purple cutaneous lesions).
Diagnostic Testing:
- Initial screening via HIV antibody/antigen immunoassays.
- Western Blot: The gold standard confirmatory diagnostic test for verifying positive HIV antibody status.

Antiretroviral medications for HIV

Medical Management:
- Antiretroviral Therapy (ART): Multi-drug regimen utilizing combination therapy with up to $4$ different drug classes (often combined into single daily fixed-dose tablets) to suppress viral replication.
- Pharmacologic Prevention: Pre-Exposure Prophylaxis (PrEP) using medications such as Truvada for uninfected individuals at high risk.
- Behavioral Prevention: Education on safe sexual practices, harm reduction, and avoiding fluid exposure.
Nursing Management and Interventions:
- Medication Adherence: Strongly encourage and monitor strict compliance with complex ART drug regimens to prevent viral resistance.
- Neutropenic Precautions: Implement protective isolation and infection control protocols when $CD4^+$ levels are severely reduced.
- High-Risk Client Counseling: Provide education and counseling on risk reduction strategies to high-risk populations.
- Nutritional Support: Offer personalized dietary support to prevent HIV-associated wasting syndrome.
- Advance Directives: Assist patients in establishing advance directives and healthcare proxy designations early in disease management.
- Occupational Safety for Nurses: Strictly adhere to universal precautions and safe needle handling techniques to prevent occupational needle-stick injuries.