Immune System - Paediatrics - Lecture Slides, Slides of Pediatrics

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THE IMMUNE SYSTEM

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The Immune System

• A. Humoral Mediated:

(B-Cell immunity; Free Ig’s) Antibodies react to bacteria by:

1. Binding directly with bacterial toxins to neutralize them
   2. Coat bacteria to enhance the phagocytosis be non-specifics components (monocytes, etc.,)

Immunodeficiency Diseases

Primary –The deficiency is the cause of disease. Primary immunodeficiencies are usually congenital, resulting from genetic defects in some component of the immune system.

Secondary – deficiency is acquired as a result of other diseases or conditions » HIV infection » malnutrition » immunosuppression

Class Relative Susceptibilities Treatment Frequency

B lymphocytes 50% bacterial infections immunoglobulin injections

T and B combined 20% viral, fungal, bacterial bone marrow and protozoal infections transplant

T lymphocytes 10% viral, fungal, and bone marrow protozoal infections transplant

Phagocytes 18% bacterial infections antibiotics, cytokines

Complement 2% bacterial infections, infusions of autoimmunity complement components

Primary Immunodeficiencies

Immunology Review

Antigen macrophage

Immunoglobulins (immediate hypersensitivity)

Plasma Cells

Transfer factor Delayed hypersensitivity

Advanced lymphcytes

Immune System T-cells Cellular thymus

B-cells Humoral Bone (Gut associated lymphoid tissue)

Adaptive immunity distinguishes self from

nonself.

• Molecules called the Major Histocompatibility Complex (MHC) identify a cell as “self” and are genetically determined.
• Anything with something different is identified as “foreign”.
• Foreign invaders are vigorously attacked.
• The system “REMEMBERS”.

Types of T-Lymphocyte

• Helper cells (T4 cells)
• Cytotoxic cells (Killer T cells)
• Suppressor cells
• Memory cells

Helper T-Cells

• Master “on-switch” of immune system
• Recognize antigens
• Secrete lymphokines that activate all other immune system cells
• Stimulate B-cells to begin antibody production

Memory T-Cells

• Have previously encountered specific antigens
• Respond in enhanced fashion on subsequent exposures
• Induce secondary immune response

Index of Suspicion

• 10 episodes acute otitis media per year

(infants and children).

• 2 episodes consolidated pneumonia per year.

• 2 life-threatening infections per lifetime.

• Two or more serious sinus infections within 1

year.

• Unusual organisms.
• Unusual response to organism.

History Our Guide

• Predominant T-Cell Defects
  • Early onset, usually 2-6 mos
  • Bacteria, mycobacteria, viruses: CMV, EBV, varicella; fungi, parasites, PCP, mycobacterium avium-intracellulare
  • FTT, protracted diarrhea, extensive mucocutaneous candidiasis
  • GVHD caused by maternal engrafment, nonirradiated blood
  • Hypocalcemic tetany in infancy

Physical Exam

• A benign physical exam does not rule out

immunodeficiency.

• Look for:
  • General appearance, weight, overall health
  • Hair, connective tissue
  • Dysmorphic features
  • Gingivitis, dental erosions, signs of sinusitis
  • Tonsillar tissue, adenopathy, splenomegaly
  • Arthritis, ataxia, neuro deficits

From the CBC

• Normal Absolute Lymphocyte Count (ALC):
  • excludes T cell defects, AIDS
  • excludes congenital and acquired neutropenias and LAD (increased ANC)
• Normal platelets:
  • excludes Wiscott Aldrich Syndrome (WAS)

Laboratory Evaluation

• T-Cell Immunity
  • Delayed-hypersensitivity skin tests
    • Intradermal injection of antigens; Candida, tetanus, trichophyton.
    • Should produce redness and induration of > 5mm by 48-72 hours.
    • Severe illness, or steroids can cause diminished responses. (anergy)
  • Mitogen testing
    • In vitro proliferative responses to concanvalin A, phytohemagglutinin