Cells and Effectors I

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Western University
Microbiology and Immunology
Microbiology and Immunology 3300B
Rodney Dekoter

LECTURE 2: CELLS AND EFFECTORS I Lecture 2 Learning Objectives 1. Learn the characteristics of the cells which comprise our immune system 2. Learn the origin and circulation of these cells 3. Learn the morphology of these cells 4. Learn the general function of these cells Epithelium – Our Barrier with the Outside World  Epithelial surfaces are parts of the body that are exposed to the outside world – this includes skin, lining of the lungs, lining of the intestinal tract, etc.  Epithelial cells are specially evolved for the specific purpose of blocking out the outside world  Generic model of epithelium - not all epithelium share the same features o Tight junctions and basement membrane are common to all epithelial cells  Tight junctions – junctions between the epithelial cells, such a tight seal that not even water or salt can get through  Basement membrane - mesh work of very strong proteins, gives epithelium physical strength and provides enough flexibility to move  There are some features that are specific to certain epithelium o Cilia - pushes mucosal fluid in and out o Epithelial surfaces like lungs have mucous in them - mucous is a sticky, viscous fluid that collects pathogens, dust, etc. o Goblet cells - specialized epithelial cells that are mucous producing factories, tend to have deep pockets within the cell o Secretory granules – synthesizes mucosal proteins, once they are full of mucus, they fuse with the deep pockets of the goblet cells causing the mucus to flow out Chemical Defenses in Epithelium  Lysozyme o Degrades bacterial cell wall o Stronger against gram-positive bacteria than gram-negative bacteria o Both gram-positive and gram-negative bacteria have a cell wall component called peptidoglycan whose purpose is to hold the cell together and resist the osmotic pressure within the cell o Lysozyme breaks down peptidoglycan o If enough damage is caused by the lysozyme, this can result in the bacteria bursting o In most cases, however, this does not occur so an additional defense is required  Secretory phospholipase A 2 o sPLA 2 o Breaks down lipid bilayer o The tails of the phospholipids that make up the membrane are targeted by sPLA an2 are cleaved off to form a lyso-phospholipid and free fatty acid – very disruptive to the membrane, causes it to bend and ultimately break  Defensins and cathelicidin function o Enzymes that are more specific in destroying membranes o Consist of a highly positively charged region and the rest of a the protein is hydrophobic o Positive region causes the protein to be attracted to membranes, as they tend to have a negative charge o Once the protein is close to the membrane, the hydrophobic region embeds itself into the membrane as the inside of the membrane is also hydrophobic – cluster together to form a pore Cells and Effector Functions  Most immune cells are in the circulation  Immune cells are not as common as red blood cells, and they have a different shape and function  Smaller immune cells are called lymphocytes and the larger immune cells are called myeloid cells  Platelets – involved in the clotting of blood Location of Immune Cells  In adults, immune cells are formed in the bone marrow  Immune cells are found throughout the body: o Blood – immune cells use blood as a way to control the body o Lymph o Central lymphoid organs o Peripheral lymphoid organs o Most tissues Blood/Lymph System  Capillaries allow small amounts of fluid to leak into tissues – oxygen and nutrients are exchanged between blood and tissue in capillary beds  This fluid accumulates antigens present within tissues  This fluid drains into lymphatic vessels  Lymph flows to peripheral lymphoid organs o i.e. lymph nodes o Immune cells “screen” lymph for antigens  Lymph returns to venous circulation, where it re-circulates through the body Composition of the Blood  Centrifuge separates components of the blood depending on how dense they are  Plasma – liquid component of blood  Buffy coat can be separated into: o Polymorphonuclear cells o Mononuclear cells Lymphoid Tissues – Bone Marrow  Spongy material found in long bones  Contains developing immune cells and erythrocytes, connective tissue and fat  Outside of the bone provides structural strength, and the middle is filled with a meshwork of small pieces of bone which acts like a scaffold – lets immune tissues grow and supports them; fat is also found in the bone marrow Hematopoiesis  The process which generates blood cells  Occurs in: o Adults: bone marrow o Fetus: egg sack  liver  bone marrow Pluripotent Stem Cell  Stem cell  Pluripotent – means it can give rise to many different cell types  Capable of “infinite” proliferation o Can divide and replicate as many times as they need to  Capable of differentiating into erythrocytes and all immune cells of the myeloid and lymphoid lineages Platelets and Erythrocytes  Platelets o Stem cell differentiates into a megakaryocyte o Megakaryocyte fragments into small cells without nucleus  platelets o Small (2-3 μm) o Stop bleeding by forming a thrombus o Thrombus = platelets “glued” together by clotting factors o Platelets are not immune cells in the sense that they attack pathogens, but they are active in the immune system as the release chemicals to stimulate the immune system when active – known as pro-inflammatory signals, also release signals to promote healing and tissue growth  Erythrocytes (Red blood cells) o Stem cell differentiates into an erythroblast
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