Immune-Lymphatic System – 2 Lymphatic Organs ANHB 2212 – 2008 Avinash Bharadwaj

Recognition of Antigens The Antigen Presenting Cell (APC) Macrophage Phagocytosis Fragmentation of foreign material Attachment to cell surface molecules (MHC) Other APCs Many sites, many types Example : Langerhans cells in the epidermis.

Lymphocytes Two major types – T and B lymphocytes Not distinguished by LM Two types of immune responses Cell mediated – direct attack by cells Humoral – antibodies as the medium (Humor : fluid. Antibodies are transported by the blood and also present in certain secretions)

Cellular and Humoral Immunity “Cell mediated” immunity. Cytotoxic T cells – Perforin, Lympotoxin, TNF Helper T cells Suppressor T cells Memory Humoral immunity B lymphocytes  plasma cells (abundant rER) Memory B cells

Exposure and Barriers External surface – skin The “open” systems Digestive and Respiratory systems – most exposed Urogenital (to a lesser extent) The epithelial barrier Integrity of epithelium Intra-epithelial defence cells Antibodies “Local” infections and non-specific defence Beyond the barrier…

Blood, Tissue Fluid and Lymph Blood capillaries “Extravasation” of fluid Tissue fluid and exchange Not all the fluid returns to blood vessels. Lymph flows through lymphatic vessels before returning to larger veins.

Lymphoid (Lymphatic) Tissues Scattered lymphocytes and other cells Lymphatic nodule – structural organisation Lymphocytes, macrophages, plasma cells, other leucocytes Outer zone (corona) and germinal centre Aggregates of lymphatic nodules Mucosa of GI Tract, respiratory system and other sites Larger aggregates – Peyer’s patches (ileum), tonsillar tissue. Organised, encapsulated structures Lymph nodes Spleen – special functions Thymus – the academy

Lymphatic Nodule “Non-capsulated” Single or aggregated Independent OR parts of other lymphoid organs Outer dark zone (Corona or cap) Germinal centre

Lymphocyte Training – Thymus Lymphoid organ Anterior Mediastinum Foetal life  Childhood  Puberty Involution in adult life

Thymus Capsule Lobules Cortex Medulla Hassal’s Corpuscles

Regions and Cells Epithelial reticular cells Capsule Cortex Lymphocytes Stages of maturation Blood vessels Barrier Capsule Cortex Medulla

Lymphocyte Training CFU-L Recognise antigen – pass/fail Recognise self/non-self – pass/fail Cytotoxic / Helper T cells

B Lymphocytes Bursa equivalent structures Bursa of Fabricius Lymphoid organ in birds Bursa equivalent structures Bone marrow Gut and other mucosa-associated structures

Tonsil A group of lymphoid structures Around the pharynx (GIT and RS) Lingual, “palatine”, tubal, nasopharyngeal Structurally similar

Palatine Tonsil Epithelium of the pharynx “Crypts” Lymphatic nodules Connective tissue and pharyngeal muscle.

Peyer’s Patches Ileum – “antimesenteric border” Lamina propria  submucosa

Lymph Node Capsulated Afferent lymphatics  “subcapsular sinus” Hilum – blood vessels, efferent lymphatic Cortex and medulla Cortex Lymphatic nodules, germinal centres “Paracortex” Medulla Medullary cords and sinusoids

C M

Lymph Node Blood vessels Cortex Lymphatics Afferent Efferent A A Lymphocytes Cortex Nodules (B) Deep cortex (T zone) Medulla (Cords, sinuses) A A A E A

Function Antigens etc APCs Nodule : B High Endothelial Vv Medulla : Plasma cells etc

Spleen Lymphatic function – lymph nodules (white pulp) around arterioles. Red pulp Sinusoids

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