T Cells: Key Players in Immunity

T Cells (T Lymphocytes)

• Central to adaptive immunity, T cells are essential for the body's targeted response to specific pathogens.
• Mature in the thymus gland, crucial for the identification and elimination of infected or malignant cells.

Helper T Cells (CD4+ T Cells)

• Assist other immune cells by secreting cytokines, enhancing the immune response.
• Activate B cells for antibody production and stimulate cytotoxic T cells and macrophages.
• Coordinate overall immune responses with specialized subtypes:
  • Th1 Cells: Target intracellular pathogens (e.g., viruses).
  • Th2 Cells: Assist responses against extracellular parasites and allergens.
  • Th17 Cells: Address fungi and extracellular bacteria; involved in autoimmune diseases.
  • Regulatory T Cells (Tregs): Suppress immune responses to maintain tolerance, preventing autoimmunity.

Cytotoxic T Cells (CD8+ T Cells)

• Directly kill infected or cancerous cells.
• Recognize affected cells via foreign antigens on MHC I molecules.
• Release perforin and granzymes to trigger apoptosis in target cells, vital for controlling viral infections and tumors.

Memory T Cells

• Provide long-lasting immunity by remembering previous infections.
• Respond rapidly upon re-exposure to previously encountered antigens, ensuring faster and effective immune responses.

B Cells (B Lymphocytes)

• Key players in adaptive immunity, maturing in the bone marrow and producing antibodies that neutralize pathogens.

Functions of B Cells

• Antibody Production: Produce immunoglobulins that bind to antigens on pathogens, neutralizing them or marking them for destruction.
• Antigen Presentation: Internalize and present antigens on MHC II to helper T cells, enhancing immune responses.
• Differentiation:
  • Plasma Cells: Produce large quantities of antibodies during infections.
  • Memory B Cells: Long-lived, they enable rapid responses upon re-exposure to antigens.

Types of Antibodies Produced

• IgM: First antibody during initial immune responses.
• IgG: Most abundant in circulation; offers long-term protection.
• IgA: Found in mucosal areas and secretions; protects body surfaces.
• IgE: Involved in allergic reactions and parasite defense.
• IgD: Serves as an antigen receptor on B cells.

Macrophages

• Large phagocytic cells from monocytes, important in both innate and adaptive immunity.

Functions of Macrophages

• Phagocytosis: Engulf and digest pathogens, dead cells, and debris.
• Antigen Presentation: Process and present antigens on MHC II to helper T cells, linking innate and adaptive immunity.
• Cytokine Production: Release cytokines to modulate immune responses, promote inflammation, and recruit other immune cells.
• Tissue Repair: Clear dead cells and stimulate tissue regeneration following injury.

Types of Macrophages

• M1 Macrophages: Pro-inflammatory; effective against infections and promote inflammation.
• M2 Macrophages: Anti-inflammatory; facilitate tissue repair and resolution of inflammation.

Other Important Immune Cells

Dendritic Cells

• Professional antigen-presenting cells critical for initiating and regulating adaptive immune responses.
• Capture antigens in peripheral tissues and migrate to lymph nodes, presenting them to naive T cells.

Natural Killer (NK) Cells

• Part of the innate immune system; can recognize and kill virus-infected and tumor cells without prior sensitization.