Immunity

OBJECTIVES List the Primary (central) Lymphoid organs Asses the function of thymus Define the Secondary (peripheral) lymphoid organs Explain the T cell educations Describe the Antigen Presenting Cells (APC)

Stem cells originate from the yalk sac in the 1st 6 wks of gestation Then the LIVER for the next few month Then the BONE MARROW will be resp. for origination & proliferation of stem cells under control of diff, hormones , enzymes & interleukin like IL3 ,IL7 ,MG CSF Macrophage granulocyte colony stimulating factor Stem cell
Lymphoid series (Lymphocyte & Nk cell)
MYELOID SERIE (RBC Granulocyte Monocyte)

Organs of Immune System

Primary (central) Thymus for T cells & bone marrow for B cells Site where lymphocyte maturation Secondary (peripheral) encapsulated (spleen & lymph node) and Unencapsulated (Mucosa associated lymphoid tissue M.A.L.T.) Site where Lymphocyte interact with Antigens & other cells

Components of Human Immune System

Thymus
2 lobs each with Cortex & medulla T Lymphocyte Education Cortex: T cells are Immature Highly dividing ,Highly dying (95%)die by Apoptosis because Auto-reactive cells ( Negative selection) Medulla less dividing less dying cells , only that recognize self MHC ( by CD4 or CD8 ) will expand( positive selection)

Cells of the thymus

Epithelial cells secrete thymic hormones as thymopoietin ,Thymoline &Thymosine also Enzymes as ADA(adenosine deaminase) & PNP (purine necleoside phosphorylase) which help in differentiation & maturation of TcellsInter –digitating dendritic cells they are rich in class II Ag & teach T cells how to deal with an Ag

Lymph node

Filters Ag from the lymph Cortex containing aggregations of B lymphocytes as a primary follicles after Ag stimulation become secondary follicles containing large dividing B lymphocytes ( blast cells & plasma cells Para cortex contains T lymphocytes


spleen
Red palp site where old RBCs are destroyed White palp surrounds the spleenic arteries forming Peri-arteriolar lymphoid sheath (area for T lymphocytes) Between red & white palp the Marginal Zone which is( area for B lymphocytes) Inter-digitating cells will take the Blood born Ag

ANTIGEN PRESENTIG CELL(APC)

Monocyte in the blood(1-6% of WBC) circulate for 3 days Tissue as a Macrophage Like alveolar cell,kupffer cell in the liver & glail cell in the Brain where they live for months & when activated they become APC where they have B7 molecule & Class II MHC Activation by phagocytosis, Gamma-interferon & cytokines from T helper cells as IL2,IL12 While IL 8 is a chemotactic

APC
Include(any cell have B7 mol.& class II MHC) Langerhans cell Dendritic cells B lymphocytes Macrophages They process the Ag & present it to T lymphocytes with class I for CD8+ cells or Class II for CD4+ cells Also they deliver B7 Mol. To react with CD28 on T helper cells

APC
APC secretes IL1, TNF, (both are endogenous pyrogen) also IL12 which activate T cells IFN α ( Anti-virus)Hydrolytic Enz., nitric oxide H2O2 , Super oxideLysozyme

Functions of APC

-Identifications of Microbes (Ag) by recognition Recptor as TL R -Engulfment (Phagocytosis) into phagosomes -Lysosomes which are filled with digestive enz. Fuse with phagosome to form phagolysosome Which will digest the Ag with preserving the Epitope -Presents the epitope in the groove of MHC class I or class II on their surface for CD8 &CD4 respectively in association with B7 molecule.

T Cells Only Recognize Antigen Associated with MHC Molecules on Cell Surfaces

Quiz choose the most appropriate answer; 1-CD4 molecule on the T helper cells recognizes a- Self Class I HLA b- Self Class II HLA C- Non self Class I HLA d- a+b 2-Primary Lymphoid organs include a- Thymus b- Lymph node c- Bone Marrow d- a +c