Cell mediated Cytotoxicity

Effector Cells Exhibiting Cytotoxic Activity

• CD8+ T cells, macrophages, and natural killer (NK) cells are the primary effector cells.

Cytotoxic T Cells (CD8+ T Cells)

• Crucial Defense: Defend against intracellular pathogens by recognizing and killing infected cells.

• Mechanisms of Killing:

  • Perforin and Granzyme: Perforin creates pores in the target cell membrane, allowing granzyme B to enter and induce apoptosis.

  • Fas Ligand (FasL): Binds to Fas receptor on the target cell, triggering apoptosis through a signaling cascade.

CD4+ Helper T Cell Activation and Roles

• Activation Process: Immature T cells interact with antigen-presenting cells (APCs) presenting pathogenic antigens.

• Cytokine Secretion: Activated CD4+ T cells (Th1 cells) secrete cytokines such as IFN-γ and IL-2 to stimulate CD8+ T cells and macrophages.

• Th1 Cells: Promote the activation and killing ability of CD8+ T cells and macrophages.

Natural Killer (NK) Cells

• Characteristics:

  • Lack Specific Antigen Receptors: Unlike T and B cells, NK cells do not have specific antigen receptors.

  • Kill Abnormal Cells: Target and destroy infected or malignant cells.

  • Activation Mechanisms: Activated by cytokines, antibody tagging, and recognition of cells lacking MHC class I markers.

• Mechanisms of Killing: Similar to CD8+ T cells, using perforin, granzyme, and Fas ligand to induce apoptosis.

Cell-Mediated Immunity (CMI)

• Role: CD8+ T cells and NK cells play critical roles in protecting against intracellular pathogens, rejecting grafts, and providing immunity against cancer.

• Mechanisms:

  • Perforin and Granzyme Pathway: Induces apoptosis in target cells.

  • Fas Pathway: Engages Fas receptors to initiate apoptosis.

Scope of Cell-Mediated Immunity

• Protection: Against viral, fungal, and intracellular bacterial infections.

• Rejection: Plays a role in graft rejection and graft-versus-host disease.

• Surveillance: Immunological surveillance against cancer.

• Pathogenesis: Involved in delayed hypersensitivity and certain autoimmune reactions.

Roles of Major Participants in Acquired Immune Response

• Humoral Immune Response:

  • B cells, helper T cells, and plasma cells produce antibodies to neutralize pathogens in extracellular fluid.

• Cell-Mediated Immune Response:

  • CD8+ cytotoxic T cells and NK cells target infected and malignant cells.

Summary of Humoral Immunity

• Stages: Antigen capture and processing by APCs, presentation, T cell activation, B cell stimulation, and antibody production by plasma cells.

Cellular Immune Response

• Activation and Function: Involves the activation of cytotoxic T cells and NK cells to target and eliminate infected cells.