Immune organs

Immune organs Central immune organs or primary lymphoid organs the site that lymphocytes generate and mature into functional cells Peripheral immune organs or secondary lymphoid organs the sites that T and B lymphocytes reside in and respond to antigens

Immune organs bone marrow thymus spleen lymph nodes Primary lymphoid organs thymus spleen Secondary lymphoid organs lymph nodes mucosal associated lymphoid tissues (MALT)

Immune organs

Section I Primary lymphoid organs I. Bone marrow the site of generation of all blood cells.

Plasticity of HSC When present in specialized tissue

HSC Theoretically, it should be possible to use stem cells to generate healthy tissue to replace that either damaged by trauma, or compromised by disease. The signal that regulate their differentiation into specialized cells are still largely unknown.

The 2012 Nobel Prize for medicine or physiology Two pioneers of stem cell research have shared the Nobel Prize for medicine or physiology. John Gurdon form UK Shinya Yamanaka from Japan

I. Bone marrow the site of B cell maturation sequential stages

II. Thymus The structure of thymus the site of T cell maturation Cortex is densely packed with immature T cells, called thymocytes. Medulla is sparsely populated with mature T cells.

The structure of thymus

Nude Mice DiGeorge syndrome a congenital birth defect in human and in mice in which the thymus fails to develop Nude Mice DiGeorge syndrome an absence of T cells and of cell-mediated immunity an increase in infectious disease

The size of the thymus is age-dependent

Section II Secondary lymphoid organs the sites that T and B lymphocytes reside in and respond to antigens spleen lymph nodes mucosal immune system (mucosal-associated lymphoid tissues, MALT)

I. Spleen 1. The structure of spleen the largest secondary lymphoid organ 1. The structure of spleen

Primary and secondary lymphoid follicle 2. Function of spleen The site of T and B cells residence T–cell area: PALS B–cell area: Primary and secondary lymphoid follicle The site that respond to blood-borne antigens

1. The structure of lymph nodes II. Lymph nodes 1. The structure of lymph nodes cortex: B cell-rich area thymus-independent area paracortex : T cell-rich area thymus-dependent area medulla : plasma cell-rich area

Primary lymphoid follicles B cells located in the follicles secondary lymphoid follicles

the path by which naive T and B lymphocytes migrate to lymph nodes

2. Function of lymphoid node The site of T and B cells residence B–cell area: cotex T–cell area: paracotex The site that respond to lymph-borne antigens

III. MALT The mucous membranes lining the digestive, respiratory, and urogenital systems have a combined surface area of about 400 m2 (nearly the size of a basketball court) the major sites of entry for most pathogens These membrane surfaces are defended by MALT

MALT loose, barely organized clusters of lymphoid cells in the lamina propria and submucosal area of gastrointestinal, respiratory and urogenital tract. well-organized structures such as tonsils and appendix, as well as Peyer’s patches

The function of MALT initiate immune responses to ingested and inhaled antigens local immunity

Section III Lymphocytes recirculation The continuous movement of lymphocytes between blood stream and secondary lymphoid organs is called lymphocyte recirculation

Significance of lymphocyte recirculation it enables the limited number of lymphocytes to search for antigen throughout the body. it ensures that particular subsets of lymphocytes are delivered to the particular tissue microenvironments.

Review 1.Terms Central immune organs, Peripheral immune organs, lymphocyte recirculation 2. Questions : Significance of lymphocyte recirculation The function of thymus, bone marrow, spleen , LN and MALT

Study question List the primary lymphoid organs and summarize their functions in the immune response. bone marrow: the site of generation of all blood cells and the site of B cell maturation. Thymus: the site of T cell maturation

Study question List the secondary lymphoid organs and summarize their functions in the immune response. 1. Spleen: The site of T and B cells residence T–cell area: PALS; B–cell area: Primary and secondary lymphoid follicle The site that respond to blood-borne antigens 2. lymph nodes: B–cell area: cotex, T–cell area: paracotex The site that respond to lymph-borne antigens 3. mucosal-associated lymphoid tissues, MALT: local immunity

Study question At what age does the thymus reach its maximal size? a. During the first year of life b. Teenage years (puberty) c. Between 40 and 50 years of age d. After 70 years of age