Immune Pathways

The adaptive immune system is comprised of two interrelated immune pathways – humoral and cell-mediated immunity

  • Both pathways involve elements of the innate immune system to coordinate their respective immune reactions

Humoral Immunity

Humoral immunity describes the pathway by which antibodies are produced by B lymphocytes to target exogenous antigens

  • When macrophages engulf exogenous pathogens, they digest them within lysosomes to release antigenic fragments
  • These fragments are presented on special surface receptors (MHC class II) that denote the material as being foreign
  • The antigens are presented to helper T cells, which in turn secrete cytokines to activate the appropriate B lymphocytes
  • The specific B lymphocytes divide and differentiate (clonal selection) to form antibody producing plasma cells

Cell-mediated Immunity

Cell-mediated immunity describes a pathway that does not result in antigen production but instead targets endogenous antigens

  • Cancerous and virus-infected cells involve the body’s own cells and thus are not recognised as foreign, evading normal detection
  • These cells may instead present antigenic fragments as a complex with their own self markers (MHC class I)
  • When helper T cells identify these cells, they stimulate a second type of T lymphocyte – cytotoxic T cells (TC cells)
  • Cytotoxic T cells show specificity to particular antigens and will bind to the presented antigen and release perforating enzymes
  • These enzymes cause the infected / cancerous cell to by lysed, preventing the further spread of infection
  • Virus infected cells can also be destroyed non-specifically by NK cells, which respond to interferon released by the infected cell

Summary of Adaptive Immune Pathways

immune pathways