Immune-Lymphatic System - 1

Introduction and Organisation

212 – 2005 – Week 8

Avinash Bharadwaj

Immunology : A vast and complex field Defence mechanisms of the body Perspectives

Molecular Cellular Histological Gross anatomical

Emphasis : histological structure of lymphoid organs Lecture 1 :

Simple concepts Lymphatic nodules, Tonsil, Lymph node

Lecture 2 : Spleen and Thymus Further elaboration of immune processes

“Getting Rid Of ”…

External attackers Viruses, bacteria, parasites…

Other “foreign” substances Particulate matter and chemicals

Our own dead cells Wayward cells An unfortunate sidelight – our own normal cells

Mechanisms

Nonspecific defence

Specific defence Cellular attack

Molecular (“humoral”) attack

More than one mechanisms may be operating at a time!

Cells involved White blood cells

Macrophages

Lymphocytes

Others

Intricate interactions between cells – molecular messengers

WBCs – Quick Review

Granulocytes Cytoplasmic granules Neutrophilic, eosinophilic or basophilic

Agranulocytes Lymphocytes Monocytes

Nonspecific Defence

Neutrophils Movement out of capillaries Phagocytosis and “digestion” Expendable force Action localised to site of infection

Other granulocytes…

Specific Defence - Immunity

Recognition of “non-self” or “foreign”. Attack Memory

Terminology Antigen – a foreign substance

Often (but not always) protein. Antibody – a protein (γ-globulin) that

specifically combines with an antigen.

Recognition of Antigens

The Antigen Presenting Cell Macrophage Phagocytosis Fragmentation of foreign material Attachment to cell surface molecules (MHC)

MHC (Major Histocompatibility Complex) Proteins unique to each individual

(Originally recognised in the context of tissue transplantation)

MHC Class I molecules present in all nucleated cells MHC Class II – in APCs – Serve to bind antigens

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 Helper T 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

Tonsils

A group of lymphoid structures Around the pharynx (GIT and RS) Lingual, “palatine”, tubal, nasopharyngeal Structurally similar Epithelium of the pharynx “Crypts” Lymphatic nodules Connective tissue and pharyngeal muscle.

Peyer’s Patches

Ileum – “antimesenteric border” Lamina propria submucosa Best seen in younger subjects

Smaller aggregates present under many mucous membranes :

“Mucosa Associated Lymphoid Tissue” or MALT

Capsulated Afferent lymphatics “subcapsular sinus” Hilum – blood vessels, efferent lymphatic Cortex and medulla Cortex

Lymphatic nodules, germinal centres “Paracortex”

Medulla Medullary cords and sinusoids

Lymph Node

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More next week!