Cellular Immunity and T-Cell Function

Introduction

• Presenter: Medicosis Perfectionatus
• Topic: Cellular immunity (T-cell immunity)
• Previous Topic: Humoral immunity (B-cell immunity)
• Key Difference:
  • B lymphocytes: Defend against bacteria.
  • T lymphocytes: Defend against viruses and fungi.

Antibodies and Their Functions

• Secreted by: Plasma cells
• Origin: B lymphocytes
• Functions upon meeting antigen:
  • Neutralization of antigen
  • Opsonization (makes it tasty)
  • Agglutination
  • Activation of natural killer cells
  • Activation of the complement system

Complement Pathways

• Three pathways:
  • Classical pathway
  • Alternative pathway
  • Mannose-binding lectin pathway

Cytokines

• Purpose: Communication between immune cells
• Components:
  • Interleukins (IL)
  • Colony Stimulating Factors (CSF)
  • Tumor Necrosis Factor (TNF)
• Etymology:
  • Cyto = Cell
  • Kines = Motion
• Types of Colony Stimulating Factors:
  • G-CSF (Granulocyte)
  • GM-CSF (Granulocyte-Monocyte)

Immunology Basics

• Antigen-presenting cells (APCs): Present antigens to lymphocytes
• Types of APCs: Macrophages, B lymphocytes, dendritic cells
• Lymphocytes:
  • Activation: Stop being naive, mature to destroy microbes
  • T helper cells (CD4): Activate B lymphocytes
  • B lymphocytes: Maturation into plasma cells or memory cells

Immune Response Types

• Humoral immunity:
  • Mediation by B lymphocytes
  • Antibodies secreted in body fluids
• Cell-mediated immunity:
  • Mediation by T lymphocytes
  • Direct cell-to-cell interaction to kill pathogens

T-Cell Types

• CD4 (T helper): Helping in various functions
• CD8 (T cytotoxic): Killing cells infected by viruses, fungi, and cancers
• CD3: Present in both types
• Activation:
  • CD8: Uses MHC class 1
  • CD4: Uses MHC class 2
• Major Histocompatibility Complex (MHC): Interaction with T cell receptor
  • Major group of proteins
  • Important for tissue compatibility
• Signals for T-cell activation:
  • First signal: MHC-TCR interaction
  • Second signal: CD80/86 with CD28

Acquired Immunodeficiency Syndrome (AIDS)

• Cause: HIV virus (RNA virus)
• Types: HIV-1 (more common and global) and HIV-2
• Effect: Targets CD4 helper T lymphocytes, weakening immunity
• Transmission: Intercourse, injections, vertical (mother to baby), breastfeeding

Pregnancy and Immunology

• Placenta: Barrier to prevent blood mixing between mother and fetus
• Unique feature: Secretes HLA-G (gestation-related)
• State: Induced immunodeficiency to protect fetus
• Risks: Avoid live attenuated vaccines during pregnancy

Autoimmune Diseases

• Mechanisms preventing autoimmunity:
  • Colonial energy (weakening potential self-attacking T lymphocytes)
  • Destruction of strong self-attacking T lymphocytes (thymus)
  • Regulation by T regulatory cells
• Examples:
  • Type 1 diabetes (autoantibodies against pancreatic beta cells)
  • Myasthenia gravis (autoantibodies against skeletal muscle receptors)
  • Celiac disease (autoantibodies in small intestine)
  • Rheumatoid lupus, others

Tissue Transplant and Blood Transfusion

• Issue: Potential for rejection
• Prevention:
  • Matching: ABO, RH, HLA before surgery
  • Suppress immunity: Using immunosuppressants (glucocorticoids, cyclosporine, etc.)
• Blood screening: Ensure no infections (HIV, hepatitis B/C)
• Complications: Hyperkalemia, hyperphosphatemia, hemoglobinemia leading to kidney damage
• New measures: Using plastic bags to prevent air embolism

Conclusion

• Summary: Importance of compatibility in immunity, prevention of autoimmune diseases, and proper processes for transplants and blood transfusions
• Promotion: Courses and subscriptions available on Medicosis Perfectionatus website