Types of lymphoid tissuesTypes of lymphoid tissues

A- Generative organs or primary lymphoid A- Generative organs or primary lymphoid organsorgans

The sites for cell proliferation and maturationThe sites for cell proliferation and maturationSuch as Bone marrow and thymusSuch as Bone marrow and thymusB- peripheral lymphoid organs or secondary B- peripheral lymphoid organs or secondary

organsorgansWhere lymphocytes responses to foreign AgsWhere lymphocytes responses to foreign AgsSuch as :spleen ,lymph nodes,cutaneous and Such as :spleen ,lymph nodes,cutaneous and

mucosal immune system .mucosal immune system .

Bone marrowBone marrow Stem cells in bone marrow express CD34 and Stem cells in bone marrow express CD34 and

stem cell antigen -1(sca-1)stem cell antigen -1(sca-1) Proliferation and maturation of precursor cells Proliferation and maturation of precursor cells

are stimulated by cytokines(CSFs)produced by are stimulated by cytokines(CSFs)produced by stromal cells and macrophagesstromal cells and macrophages

Plasma cells,stem cells and their progenyPlasma cells,stem cells and their progeny

ThymusThymus The site of T cell maturationThe site of T cell maturation Bilobed organ divided into multiple lobules Bilobed organ divided into multiple lobules

and each lobule consists of an cortex and an and each lobule consists of an cortex and an medula medula

Thymus contain thymocytes and non lymphoid Thymus contain thymocytes and non lymphoid cellscells

Chemokines for entry to thymus:CCR9(pre-T)-Chemokines for entry to thymus:CCR9(pre-T)-CCL25(cortex)CCL25(cortex)

Chemokines for movement from cortex :CCR7- Chemokines for movement from cortex :CCR7- CCL19,21(medula) CCL19,21(medula)

Why peripheral lymphoid tissuesWhy peripheral lymphoid tissues??

1)To optimise the cellular interaction , 1)To optimise the cellular interaction , lymphocyts and APCs are localised and lymphocyts and APCs are localised and concentrated in anatomically defined tissues.concentrated in anatomically defined tissues.(immune response)(immune response)

2)The sites where foreign Ags are transported 2)The sites where foreign Ags are transported and concentrated. (Ag trapping)and concentrated. (Ag trapping)

Peripheral lymphoid tissuesPeripheral lymphoid tissues(lymph nodes)(lymph nodes)

The skin ,epithelia and parenchymal organs contain many lymphatic vessels that absorb and drain interstitial fluis from this sites.

The absorbed interstitial fluid , called lymph.

((lymph nodelymph node))

* *The Cortex consist of folliclesThe Cortex consist of follicles * *Follicles are the B cell zones of Follicles are the B cell zones of

lymph nodeslymph nodes * *The T cells are located beneath The T cells are located beneath

and between the folliclesand between the follicles * *The naThe naïïve T cells express CCR7 ve T cells express CCR7

and its ligand is CCL19 ,CCL21and its ligand is CCL19 ,CCL21 * *The naThe naïïve B cells express CXCR5 ve B cells express CXCR5

and its ligand is CXCL13and its ligand is CXCL13

((spleenspleen))

* Major site of immune responses to blood borne antigens.

* White pulp:

a) Periarteriolar lymphoid sheaths(PALS) is the T cell zone of spleen

b) Lymphoid follicles

c) The Marginal zone is a rim of lymphocytes and macrophages that surround the follicles

*individuals lacking a spleen are extremely susceptible to infections with encapsulated bacteria

White pulp