Immune-Lymphatic System - 1

Introduction and Organisation

212 – 2004 – Week 8

Avinash Bharadwaj

Immunology Et cetera…

Defence mechanisms of the body Perspectives

Molecular Cellular Histological Gross anatomical

Immunology Et cetera…

A vast and complex field Introduction and overview

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))

T Lymphocytes

“Cell mediated” immunity. Helper T cells

Interleukins : relevant responses from other cells Cytotoxic T cells – Perforin, Lympotoxin, TNF Suppressor T cells – Interleukins control the reaction Memory

B Lymphocytes

Humoral immunity Helper T cells Interleukins activation – mitosis large number of

B cells against the same antigen. B lymphocytes plasma cells (abundant rER) Antibodies work in various modes 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 Chemical factors 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), tonsilar tissue.

Organised, encapsulated structures Lymph nodes Spleen – special functions Thymus – the academy

Lymphatic Nodule

Outer dark zone (Corona or cap)

Germinal centre

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

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More next week!