3. Lymphoid System - Notes taken from the lecture of Sir Joseph Joy Banzon, RMT PDF

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IMMUNOLOGY SEROLOGY IMMUNE SYSTEM IMMUNE SYSTEM includes Lymphoid system as its vital part computerized war machine of the body MAJOR FUNCTIONS OF THE IMMUNE SYSTEM: Block harmful agents invasive pathogens Isolate Neutralize activity of that antigen CELLS OF THE IMMUNE SYSTEM: 1. MYELOID LINEAGE: Mo...

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IMMUNOLOGY & SEROLOGY

IMMUNE SYSTEM IMMUNE SYSTEM - includes Lymphoid system as its vital part - computerized war machine - “defense department” of the body MAJOR FUNCTIONS OF THE IMMUNE SYSTEM:  Block harmful agents  Seek-out invasive pathogens  Isolate & Neutralize activity of that antigen CELLS OF THE IMMUNE SYSTEM: 1. MYELOID LINEAGE: Monocytes & Granulocytes 2. LYMPHOID LINEAGE: Lymphocytes ACQUIRED / SPECIFIC IMMUNITY - type of resistance that is characterized by specificity for each individual pathogen & the ability to remember prior exposure, which results in an increased response upon repeated exposure LYMPHOCYTES - the key cell involved in the Adaptive immunity - represent between 20-40% of the circulating WBCs  Size: between 7-10 µm in diameter  Nucleus: large, round, & indented  Chromatin: dense & stains deep blue  Cytoplasm: sparse, stains light blue, containing few organelles  but no specific granules LYMPHOPOIESIS - production of Lymphocytes Stages of Lymphopoiesis: 1. ANTIGEN INDEPENDENT STAGE OF LYMPHOPOIESIS - occurs on the Primary lymphoid organs - without the involvement of Antigens 2. ANTIGEN DEPENDENT STAGE OF LYMPHOPOIESIS - occurs on the Secondary lymphoid organs - with the involvement of Antigens LYMPHOID SYSTEM - a system in the body which consist of lymph vessels, lymph nodes, & lymph fluids. Its primary function is to transport Lymph, a colorless fluid containing Lymphocytes that help rid the body toxins, waste, & other unwanted materials

JOYCE ANN S. MAGSAKAY

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BS MEDICAL LABORATORY SCIENCE

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OLFU VALENZUELA

IMMUNOLOGY & SEROLOGY

IMMUNE SYSTEM COMPARTMENTS OF LYMPHOID SYSTEM: PRIMARY / CENTRAL LYMPHOID SYSTEM - serves as the developmental sites 1. BONE MARROW - largest primary lymphoid organ - Weight: 1,300-1,500g (adult) - it is where B-cell maturation occurs - main source of Hematopoietic stem cells - center for Antigen-Independent Lymphopoiesis 2. THYMUS - small, flat bilobe organ found in thorax or chest cavity right below Thyroid gland & overlaying the Heart - Weight: 30g (birth), 35g (puberty) then Atrophies - it is where T-cell maturation occurs - produces “Thymosin” which promotes maturation of T-cell - although it diminishes in size, it is still capable of producing T-Lymphocytes until at least the 5th or 6th decade of life - T-cell progenitors appear in the fetus as early as 8 weeks in gestational period Parts of Thymus:  CORTEX: where Thymocytes can be found  MEDULLA: where mature T-cell can be found  THYMIC STROMAL CELLS: include epi cells, macrophages, & dedritic cells which serves as APC & MHC II. SECONDARY / PERIPHERAL LYMPHOID SYSTEM - serves as the activation sites  Encapsulated Organs: 1. SPLEEN - largest secondary lymphoid organ - Weight: 150 g – Length: 12 cm - located in the upper-left quadrant of the abdomen, just below the diaphragm & surrounded by thin connective tissue capsule - characterized as “large discriminating filter” as it removes old, damaged cells & foreign antigens - Lymphocytes enter this area via Specialized Capillaries on Marginal Sinus & via Trabecular Artery - an adult’s blood volume passes through spleen for about 4 times each day I.

Types of Splenic Tissue: a. WHITE PULP - comprises 20% of the total weight - contains the Lymphoid tissue, which is arranged around arterioles in a PERIARTERIOLAR LYMPHOID SHEATH (PALS) where T-cells can be found JOYCE ANN S. MAGSAKAY | BS MEDICAL LABORATORY SCIENCE | OLFU VALENZUELA

IMMUNOLOGY & SEROLOGY

IMMUNE SYSTEM Parts of White Pulp:  CENTRAL ARTERIOLE: where T-cells are found  PRIMARY FOLLICLES: Naïve/Virgin/ Resting B-cells are found  SECONDARY FOLLICLES: Activated B-cells are found  MARGINAL ZONE: contains macrophages & APC  GERMINAL CENTER: indicator that cells are actively multiplying & dividing b. RED PULP - makes up 80% of the total weight - involved in the culling, pitting, & platelet sequestration 2. LYMPH NODES - the “junctional filter” of the lymphoid system - Size: 1mm-25mm - located along Lymphatic ducts - especially numerous in joints, arms, & legs of the body - the central collecting points for lymph fluid from adjacent tissues - Filtration & generation of memory B-cell is its main function - Lymph fluid flows slowly through spaces called “SINUSES” which are lined with macrophages, creating an ideal location for Phagocytosis to take place - Lymphocytes enter this area via Afferent Lymphatic vessels & by Specialized venules called “HIGH ENDOTHELIAL VENULES” located in Paracortical areas & exits via Efferent Lymphatic vessels - Particulate antigens are removed as the fluid travels across the node from Cortex to Medulla within 18hrs - If contact with antigen takes place, the Lymphocyte traffic shuts down due to proliferation of activated cells Layers of Lymph Nodes:  CORTEX - B-cell area - has Macrophages & Specialized cells called “FOLLICULAR DENDRITIC CELL” - contains Primary follicles with small amounts of T-cell & Secondary follicles that has interior called “GERMINAL CENTER” where blast transformation of B-cell takes place  PARACORTEX - T-cell area - the region between follicles & medulla - T-Lymphocytes are in close proximity to antigen-presenting cells called “INTERDIGITATING CELLS”  MEDULLA - less densely populated but contains some T-cells, Macrophages, & Plasma cells  Non-Encapsulated Lymphoid Organs: 1. MUCOSAL-ASSOCIATED LYMPHOID TISSUE (MALT) - found in Intestinal, Genitourinary, & Respiratory tract 2. BRONCHUS-ASSOCIATED LYMPHOID TISSUE (BALT) - found in Tonsils & Adenoids 3. GUT-ASSOCIATED LYMPHOID TISSUE (GALT) - includes Peyer’s Patches & Appendix 4. CUTANEOUS-ASSOCIATED LYMPHOID TISSUE (CALT) - includes Intra-epidermal lymphocytes JOYCE ANN S. MAGSAKAY | BS MEDICAL LABORATORY SCIENCE

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OLFU VALENZUELA

IMMUNOLOGY & SEROLOGY

IMMUNE SYSTEM LYMPHOCYTE TRAFFIC / RECIRCULATION - movement of lymphocytes from blood to lymphoid organs & back to blood HOW WILL T-CELLS & B-CELLS FIND ITS WAY TO THE LYMPH NODE??? - through POST CAPPILARY TRAFFIC ENDOTHELIAL VENULE / HIGH-WALLED ENDOTHELIAL VENULE (HEV) - has ADDRESINS, which composed of CD-32 & CD-102 together with other adhesion molecules - T-cells & B-cells have Homing rececptors which is called “LEUKOCYTE ADHESION MOLECULE” (LAM) or L-SELECTIN STAGES OF B-CELL DIFFERENTIATION:

1. PRO-B CELLS - rearrangement of genes that code for the heavy chains & light chains of an antibody molecule - has Growth factors such as:  E2A necessary to differentiate common lymphoid precursors against pro-B cells  EARLY B-CELL FACTOR (EBF)  PAIRED BOX PROTEIN-5 (PAX) - has Intracellular Proteins such as:  Terminal Deoxyribonucleotide Transferase (TdT): attach the DNA fragment to another one  Recombination-Activating Genes (RAG-1) & (RAG-2): cleaves the DNA at possible recombination sites - has distinctive markers such as:  CD19: acts as coreceptor that helps regulate further B-cell development & activation  CD24:  CD45R: largest form of CD45 found on B-cells  CD43:  C-KIT: interacts with a Stem cell factor which is found on stromal cells which triggers the activation process - Interleukin-7 (IL-7) is also necessary at this early developmental stage Parts of B-cell Surface Antibody: composed of 4 polypeptide chain a. 2 identical HEAVY CHAIN - coded on Chromosome 14 - has 5 types: Alpha, Beta, Gamma, Epsilon, & Mu b. 2 identical LIGHT CHAIN - has 2 types: Kappa (Chromosome 2) & Lambda (Chromosome 22) 2. PRE-B CELLS - begins when the heavy chain part of the Ab molecule are formed - it starts to lose CD43, TdT, & C-Kit JOYCE ANN S. MAGSAKAY | BS MEDICAL LABORATORY SCIENCE | OLFU VALENZUELA

IMMUNOLOGY & SEROLOGY

IMMUNE SYSTEM - Mu chains are the first heavy chain to be synthesized are accompanied by unusual light chain called “ SURROGATE LIGHT CHAIN” & “VERY SHORT CHAINS Ig-α/Ig-β” forms the PRE-B CELL RECEPTOR, which adheres to bone marrow stromal cell membranes & transmits a signal to prevent rearrangement of heavy chain genes - only existing B-cells expressing the Mu chains & Surrogate light chains survive & proceed to further differentiation 3. IMMATURE B-CELLS - earliest stage to predict the Ag specificity of the B-cell (by VARIABLE REGION) - B-cells capable of producing Ab to self-Ag are deleted in the bone marrow through APOPTOSIS - distinguished by the appreance of complete IgM molecules which indicates that rearrangement of the genetic sequence coding for light chains on either Ch2 or Ch22 has taken place - include surface markers for Complement Component such as:  CD3: receptor for Epstein-Barr Virus (EBV)  CD21: acts as receptor for a breakdown product of Complement Component C3 /C3d  CD40 Important for the interaction of B-cells & T-cells  MHC Class II 4. MATURE B-CELLS - mature B-cells exhibit both IgM & IgD on their cell surface  MARGINAL ZONE B-CELLS: remain in the spleen in order to respond quickly to any blood-borne pathogens  FOLLICULAR B-CELLS: found constantly recirculating to secondary lymphoid organs 5. ACTIVATED B-CELLS - exhibit CD25 & acts as a coreceptor to IL-2, responsible for the proliferation & multiplication - Antigen-dependent activation takes place in the primary follicles of Peripheral Lymphoid tissue - it occurs when Ag cross-link several surface Ab on the B-cells, causing it to transform into blast, which will give rise either to plasma cells or memory cell 6.1 PLASMA CELLS - spherical, ellipsoidal cells that contain abundant cytoplasmic Ig & little to no surface Ig - Size: 10-20 um - Nucleus: Eccentric or Oval - Chromatin: heavily clumped that stains darkly - Cytoplasmic: has abundant Endoplasmic Reticulum (ER) & clear well-defined Golgi zone - considered as the “most fully differentiated lymphocyte” - its main function is to produce Antibodies - not normally found in the blood but located in germinal centers in the peripheral lymphoid organs - they are non-dividing, has short life-span, & after days of producing antibodies, they die without further proliferation 6.2 MEMORY CELLS - also found in the germinal centers in the peripheral lymphoid organs - represent the progeny of antigen-stimulated B-cells that are capable of responding to Ag w/ ↑ speed & intensity - they are similar to the appearance to Unstimulated B-cells, but they have longer life-span STAGES OF T-CELL DIFFERENTIATION: 1. PRO-THYMOCYTE - include surface markers CD44 & CD25 - they go through gene rearrangement same as with B-cell which takes up to 3 weeks

JOYCE ANN S. MAGSAKAY

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BS MEDICAL LABORATORY SCIENCE

|

OLFU VALENZUELA

IMMUNOLOGY & SEROLOGY

IMMUNE SYSTEM - has Intracellular Proteins such as:  Terminal Deoxyribonucleotide Transferase (TdT): attach the DNA fragment to another one  Recombination-Activating Genes (RAG-1) & (RAG-2): cleaves the DNA at possible recombination sites - Interleukin-7 (IL-7) is also necessary at this early developmental stage Parts of T-cell Receptor: composed of 8 polypeptide chain a. CD-3 - comprises the 6 polypeptide chains - the constant region of the T-cell b. VARIABLE REGION - it can be Alpha or Beta - the variable region of the T-cell 2. DOUBLE NEGATIVE THYMOCYTES - possess CD2, CD5, CD7, & CD45R; - but lack CD4 & CD8 antigens - actively proliferating in the outer cortex under the influence of IL-7 3. DOUBLE POSITIVE THYMOCYTES - express both CD4 & CD8 antigens as well as CD3-αβ (TCR) - would undergo:  POSITIVE SELECTION: Any Thymocytes unable to respond to self-MHC Ag die without leaving the Thymus  NEGATIVE SELECTION: the surviving double positive T-cell that has strong reactions with self-Ag are deleted 4. MATURE T-CELLS - T-cell survivors of both Positive & Negative selection must only exhibit one type of marker, either CD4 or CD8 5.1 T-HELPER (INDUCER) CELLS - recognizes Ag along with MHC Class II - possess CD4 antigen Subsets of T-Helper cells: a. Th1: produce Interferon gamma (IFN-γ) & Tumor Necrosis Factor-Beta (TNF-β) which protect cells from Ag b. Th2: produce different interleukins such as IL-4, IL-5, IL-10, IL-13 which helps the B-cell to produce Ab against Ag 5.2 T-CYTOTOXIC CELLS - recognizes Ag along with MHC Class I - possess CD8 antigen 5.3 T-REGULATORY CELLS - possess CD4 & CD25 antigen - comprises of 5-15% of all CD4 (+) T-cells - suppresses the immune response to self-antigens by producing IL-10 & Growth factor-B COMPARISON OF T-CELLS & B-CELLS T-CELLS B-CELLS develops in the Thymus Develops in the Bone marrow B-CELLS FUNCTIONS Thoracic duct fluids, & lymph nodes found inT-CELLS Bone Marrow, Spleen, & lymph nodes FUNCTIONS + B-cell B1 found in Blood,- CD5 Identified by Rosette with Sheep RBC Identified by Surface immunoglobulins T-HELPER - IgM >formation IgG End product of- activation: End product ANTIBODIES immunity - Cell-mediated * Th1 of activation: reacts withCYTOKINES Thymus Independent Ag Antigens include: CD2, CD3, CD4, & CD8 Antigens include: CD19, CD20, CD21, CD40 & MHC Class II * Th2 - capable of producing Autoantibodies - Humoral immunity Located in the paracortical region of lymph nodes Located in the cortical region of lymph nodes cells T-CYTOTOXIC - kills Virus & Cancer - “Transitional B-cell” B1-A - IgM = IgG T-REGULATORY - prevents Autoimmune diseases - reacts with Thymus Dependent Ag γ δ T-CELLS - resembles NK cells - “Conventional B-cell” JOYCE ANN S. MAGSAKAY | BS MEDICAL LABORATORY SCIENCE | OLFU VALENZUELA - IgM < IgG B2

IMMUNOLOGY & SEROLOGY

IMMUNE SYSTEM NATURAL KILLER CELLS (NK-CELLS) - it is larger than T-cell & B-cell - has high N:C ratio - contains a kidney-shaped nucleus with condensed Chromatin & prominent nucleoli - also called as “Large granular lymphocytes” & “Primitive T-cytotoxic cells” because it resembles the function of T-cytotoxic cells but it doesn’t need to associate with MHC to function - constitutes to the 5-15% of the circulating lymphoid pool - found mainly in the spleen & blood - has no specific surface markers - possess CD16, CD56, & CD94 - it acts as Anti-cancer & Anti-viral cell - plays complementary role to CD8+ T-cells - in response to IL-2, it becomes “Lymphokine Activated Killer Cell” (LAK) which is the most potent type of NK cell MECHANISM OF NK-CELL CYTOTOXICITY: 1. It is brought by the balance between activating & inhibitory signal that enable NK cells to distinguish healthy cells from infected or cancerous cells  MHC CLASS I: present in all healthy cells  KILLER CELL INHIBITORY RECEPTORS (KIR): giving a stimulus not to the destroy the healthy cells  NKG2D: binds to MICA & MICB, a stress proteins on infected or cancerous cells  If an inhibitory signal is not produced, NK cells will release:  PERFORINS: create channels on the NK cells in order to insert GRANZYMES: which will kill the infected cells 2. Antibody-Mediated Cell Cytotoxicity: through binding of IgG-coated cell with CD16 LABORATORY IDENTIFICATION OF LYMPHOCYTES: 1. DENSITY GRADIENT CENTRIFUGATION WITH FICOLL-HYPAQUE - one way of isolating Lymphocytes form the whole blood - whole blood with Ficoll-Hypaque is carefully will be subjected to centrifuge @ 4003 g for 30mins - Centrifugation will produce three distinct layers: (1) Plasma, (2) Mononuclear layer , (3) RBC & Granulocytes 2. FLOW CYTOMETRY - once the lymphocyte is isolated, segregation into subset next - relies on the use of labeled monoclonal antibodies against specific Ab antigens  T-CELLS: CD2, CD3, CD4, CD7, & CD8 for T-cells  B-CELLS: CD19, CD20, CD22, for B-cells

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CELL FLOW CYTOMETRY / FLUORESCENCE ACTIVATED CELL SORTER: an automated system for identifying cells based on the scattering of light as cells flow in single file through a laser beam - FLUORESCENT ANTIBODIES are used to screen for subpopulations such as B-cells, T-helper cells, & T-cytotoxic cells - these antibodies are MONOCLONAL, & each has a different FLUORESCENT TAG Components:  Sample Delivery System  A laser for Cell Illumination  Photodetectors for signal detection  Computer –based management system 3. FLUORESCENCE MICROSCOPY JOYCE ANN S. MAGSAKAY | BS MEDICAL LABORATORY SCIENCE | OLFU VALENZUELA

IMMUNOLOGY & SEROLOGY

IMMUNE SYSTEM a. DIRECT IMMUNOFLUORESCENCE - use Monoclonal Antibodies with a Fluorescent tag - Example: Fluorescein, Phytoeryhtrin (490 nm), & Rhodamine (545 nm) b. INDIRECT IMMUNOFLUORESCENCE - uses unlabeled Ab that first combines with the Ag by itself & a second Ab that is complexed with a dye 4. ROSETTE TECHNIQUE - one the lymphocyte is isolated, it will be mixed with a suspension of Sheep RBC - If three or more RBC are attached to a lymphocyte, it is considered as Rosette. - Sheep cells attach to CD2 antigen, found only on T-cells - 200 cells will be counted using counting chamber. This represents the percentage of T-cells, & the percent of B-cells is calculated by subtracting this number from 100 - There should be approximately twice as many T-cells as B-cells- It is not precise because resetting can be influenced by cold-reacting anti-lymphcyte antibodies 5. EZYME-LINKED IMMUNOASSAY (ELISA) - it also counts T-cell & B-cells using Monoclonal antibodies & fluorescence but differ in Antibody labels

JOYCE ANN S. MAGSAKAY

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BS MEDICAL LABORATORY SCIENCE

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OLFU VALENZUELA...