Cell Mediated Immunity

Overview

• Cell mediated immunity is a branch of adaptive immunity.
• It is responsible for targeting pathogens that hide inside the body's own cells, such as viruses and some bacteria.

Comparison with Humoral Immunity

• Humoral Immunity: Targets pathogens in body fluids like blood and lymph.
  • Key cell type: B cells (B lymphocytes).
• Cell Mediated Immunity: Targets pathogens inside body cells.
  • Key cell type: T cells (T lymphocytes).

T Cells (T Lymphocytes)

• T cells mature in the thymus.
• Key roles:
  • Helper T cells (CD4+ T cells): Act as "generals" in the immune system.
  • Cytotoxic T cells (CD8+ T cells): Act as "ground troops," targeting and destroying infected cells.

Activation of B Cells in Humoral Immunity

• B cells act as antigen-presenting cells (APCs) when they bind to specific antigens.
• B cells present antigens to Helper T cells.
• Helper T cells secrete chemicals to activate B cells.
• Activated B cells divide into plasma cells, producing antibodies.

Activation of T Cells in Cell Mediated Immunity

• Helper T cells activate other T cells, including cytotoxic T cells, through a two-step process:
  1. Activation of Helper T Cells:
     • Dendritic cells or other APCs display antigens to Helper T cells.
     • Helper T cells bind and get activated.
  2. Co-stimulation:
     • Activated Helper T cells stimulate APCs to develop new surface receptors.
     • These receptors allow cytotoxic T cells to bind and become activated.

Cytotoxic T Cells

• Target and destroy infected host cells.
• Utilize lysis to destroy cells:
  • They puncture cell membranes, causing cell contents to spill out, leading to cell death.

Role in Immunity

• Helper T cells coordinate both humoral and cell mediated responses.
• Ensure that pathogens both in body fluids and inside cells are targeted effectively.