Tissues of the Immune System Supplementary slides

There are 2 types of tissues Primary and Secondary lymphoid tissues Lymphatic vessels connect the secondary lymphoid tissues to the organ tissues and the bloodstream and thus to sites of infection PRIMARY LYMPHOID TISSUE (BONE MARROW & THYMUS) SECONDARY LYMPHOID TISSUE (Spleen. Lymph nodes, MALT)

Lymphocyte circulation

Mature T-lymphocytes exit the thymus and enter the blood stream Specialised APCs (like dendritic cells) travel to an inflamed tissue and collect antigen They leave the blood and drain into the lymph where they take the antigen to the lymph node. They enter the lymph node through the AFFERENT lymphatic vessel. The T lymphocytes that are circulating between the blood and the lymph node enter the node through the HEV. T lymphocytes get activated by the APCs and they leave the lymph node through the EFFERENT lymphatic vessel and then enter the blood.

Lymphocyte circulation

Secondary lymphoid tissue Lymphatics = lymphatic vessels Lymph nodes  Armpits, groin, neck and along small intestine  Collect antigen from the affected tissue Spleen  Left side of abdomen  Collects antigen directly from bloodstream MALT (mucosa associated lymphoid tissue)  Particularly well-organised in Peyer’s patches  Collect antigen from respiratory, gastrointestinal and urogenital tracts

Secondary lymphoid tissue The lymph nodes are connected to the tissue and the bloodstream by a system of lymphatic vessels  The AFFERENT lymphatic drains extracellular fluid (lymph) from tissues and mucosal tissues into the lymph nose. APCs bring antigen to naïve, circulating T lymphocytes through this vessel  The EFFERENT lymphatic vessel carries the lymph with activated lymphocytes out of the secondary lymphoid tissues and into a collecting cessel known as the thoracic duct (in the cest) or cervical duct in the neck and hence through the heart and into the blood stream.

Overview of Immune Responses to Microbes EARLY INNATE IMMUNE RESPONSE Epithelia of Skin, GI & Respiratory tracts Phagocytes (neutrophils, macrophages) ingest & destroy pathogens Release of natural antimicrobial agents Dendritic cells secrete cytokines -> lymphocyte response Natural killer cells Kill virus infected cells and produce IFN-gamma -> macrophage activation

Cell-Mediated Immunity Naive T cells are activated by APCs in the lymphoid organs -> secrete cytokines -> proliferation and differentiation -> T H & CTCs may migrate back into the blood at site of infection -> eT cell is reactivated by Ag -> eliminate pathogen T H cell  Produce cytokines  Bind to B cells -> promote Ab production  Bind to macrophages -> promote killing of ingested microbe  Recruit and activate neutrophils

Antibody mediated immunity Antibodies  Bind to microbes and prevent them from infecting dells  Coat (opsonize) microbes and target them for phagocytosis  Activate the complement system that promote phagocytosis and destruction of pathogens