Section 1: Introduction to Immunology Flashcards
Immunology
the study of the physiological mechanisms that organisms used to defend themselves against invasion against other organisms
How did the study of immunology begin
-with the observation that survivors of an epidemic infectious disease usually were unaffected upon subsequent exposure to the same disease
-these survivors had become immune to infection
What collectively forms the immune system
-system of cells, molecules, and enzymes that an organism dedicates to defense
-majority of immune system found along GI tract
What is the immune system designed to defend against?
- bacteria
- viruses
- fungi
- parasites
-but not all microorganisms are harmful
commensal organisms
are organisms that coexist on and in the human body, and are tolerated by the immune system that forms a mutualistic relationship
- “eat at the table”
-sometimes are mutualistic in which they protect us from harmful organisms
mutualism
-each organism gains a fitness advantage
ex: the bacteria that live within your gut normal gastrointestinal floral are crucial in digestion and absorption of nutrients and protection against harmful organisms
pathogenic organisms
- pathogens, are microorganisms that have the potential to cause diseases
human microbiome
the collection of normally occurring (commensal) microorganisms that live in or within the human body
-500-1000 different species of organisms occupy the human microbiome (mostly in gut)
- 10^13 cells make up human body, estimated 10^14 bacterial cells living in the body
-every 1 cell of you there are 10 bacterial cells
-probably 10^15 viruses and phages
innate immune system
refers to immunity that is defined entirely at birth
-quick response
- relatively non-specific
-does not improve upon immediate exposure
-two arms of the immune system that recognize self from non-self (innate and adaptive)
adaptive immune system
-cannot have an adaptive immune response without a innate immune response
-refers to immunity that is developed (adapted) during an infection to a specific pathogen
-slower to respond than innate
-specific to a certain pathogen
-develops memory (improved response upon repeated exposure)
What is the first obstacle most pathogens have to overcome first
-the skin, a physical barrier that prevents entry into the body
epithelium
a tough layer of keratinized cells that line the outer surface and inner cavities of the body
-the skin and the commensal bacteria on it contribute to the innate immunity
continuous with the skin are the epithelial lining the
- respiratory
- gastrointestinal
- urogenital tract
*mucosal surfaces have the first interaction with the outside world
*key areas where immune system will reside
mucosal surfaces
are specialized epithelial surfaces lining the internal cavities of the body that
1. bathe in a mucous layer they secrete
2. more vulnerable to infection
3. designed to communicate, interact with outside world (lumen)
4. vary in cellular organization and specialization depending on the site
mucus
a thick fluid that protects against microbial invasion
-mechanical flow of fluid (cilia, respiratory tract)
-glycoproteins, proteoglycans, and enzymes
- pH can help protect against infection
defensins
antimicrobial peptides that disrupt membranes
-located in mucosal surfaces
Mechanical action of skin
-flow of fluid, perspiration, sloughing off the skin
chemical action of skin
-sebum (fatty acids, lactic acid, lysozyme)
microbiological action of skin
normal flora of skin
mechanical action of gastrointestinal tract
flow of fluid, mucus, food, and saliva
chemical action of gastrointestinal tract
acidity, enzymes (proteases)
microbiological action of gastrointestinal tract
normal flora of the gastrointestinal tract
mechanical action of respiratory tract
flow of fluid and mucus, by the cilia, air flow
chemical action of respiratory tract
lysozyme in nasal secretions
microbiological action of respiratory tract
normal flora of the respiratory tract
mechanical action of urogenital tract
flow of fluid, urine, mucus, sperm
chemical action of urogenital tract
acidity in vaginal secretions, spermine and zinc in semen
microbiological action of urogenital tract
normal flora of the urogenital tract
mechanical action of the eyes
-flow of fluid, tears
chemical action of the eyes
lysozyme in tears
microbiological action of the eyes
normal flora of the eyes
The innate response contains two steps
- recognition
- effector mechanism
recognition
the pathogen is recognized by soluble proteins and cell surface receptors that bind to the pathogen or its products
effector mechanisms
after recognition , effector cells of various types are recruited to fight the pathogen
recognition receptors proteins bind to a diverse set of ligands such as
- peptides
- proteins
- glycoproteins
- peptidoglycan
- proteoglycan
6.carbohydrates - glycolipids
- phospholipids
- nucleic acids
inflammation
-the innate immune response establishes inflammation at the site of an infection
How is inflammation characterized
Heat (calor)
Redness (rubor)
Swelling ( tumor)
Pain (dolor)
-each characteristic is associated with a specific function of the innate immune response induced at site of infection
cytokines
are soluble proteins that bind to specific receptors on various cell types and trigger a set of responses
-after a pathogen is recognized by an effector cell, inflammation is initiated by release of this
-immune system uses this to communicate to each other or other cells
Inflammatory cytokines induce
- vasodilation
- edema
- extravasation
- recruitment
* the accumulation of cells and fluid in and around the infection site causes skin to warm (redden, swell) which puts pressure on the nerve endings resulting in pain
vasodilation
increases blood flow to the tissue, decreases laminar flow within the blood vessels, and the endothelium becomes permeabilized (gaps between cells)
edema
expansion of the local blood volume causes swelling of the connective tissue
extravasation
the movement of cells or fluid from within the blood vessels to the surrounding tissue
recruitment
change in the cellular adhesion properties of the endothelial cells (not chemotaxis –> chemokines (diffusion gradient and a cell will follow that reverse gradient to get to a certain site))
Clonal selection and expansion
-part of adaptive immunity
-the effector functions used by the innate and adaptive immune systems are similar but the receptors and mechanisms used to detect pathogens are different
-during the adaptive immune response lymphocytes that have receptors which can recognize pathogen specific antigens are selected to participate in the adaptive response
antigen
any molecule or molecular fragment (Epitope) that can be bound by a major histocompatibility complex (MHC) molecule and presented to a T-cell receptor (TCR)
epitope
the portion of an antigenic molecule that is bound by an antibody (Ab) or gives rise to the MHC binding peptide that is recognized by a TCR
clonal selection
the central principle of adaptive immunity , the mechanism by which adaptive immune responses derive only from individual antigen-specific lymphocytes
clonal expansion
lymphocytes are stimulated by the antigen to proliferate and differentiate into antigen-specific effector cells
primary immune response
-the severity of the first encounter with an infectious disease arises because this response is developed from very few specific lymphocytes
-it takes time for expansion thus giving the pathogen time to establish an infection
-the clones from this response include a population of long lived memory cells which will respond quicker and with more force the subsequent encounters with the pathogen (secondary immune response)
-this is the basic concept of immunization
Innate and adaptive immunity are linked
-all adaptive immune responses are contingent upon an innate immune response
-it is important to have both effectively combat infections
-without adaptive infection can bypass the innate immune response and take control
-without the innate immune response you cannot mobilize an effective adaptive immune response
cells of the immune system
white blood cells (leukocytes) or immune cells with different functions all derive from hematopoietic stem cells
-continuously being made through a process called hematopoiesis
-after birth hematopoiesis being takes place in the BONE MARROW and progenitor pluripotent hematopoietic stem cells give rise to
1. erythrocytes (red cells)
2. megakaryocytes (platelets)
3. leukocytes (white cells)
small lymphocyte
production of antibodies (B cells) or cytotoxic and helper function (T cells)
- 20-50% found in body
dendritic cell
activation of T cells and initiation of adaptive immune response
-account for less than 1 % of leukocyte population in circulation and tissues
-rarest and most important to the immune system
plasma cell
-fully differentiated form of B cell that secretes antibodies
mast cell
expulsion of parasites from body through release of granules containing histamine and other active agents
natural killer cell
kills cells infected with certain viruses
monocytes
circulating precursor cell to macrophage
- 2-10 % found in body
neutrophil
phagocytosis and killing of microorganisms
-40-75 % found in body
macrophage
phagocytosis and killing of microorganisms
-activation of T cells and initiation of immune response
eosinophil
killing of antibody-coated parasites through release of granule contents
- 1-6 % found in body
basophile
controlling immune responses to parasites
- <1 % found in body
megakarocytes
platelet formation, wound repair
-produce platelets
erythrocyte
oxygen transport
Lymphoid tissues (organs)
-we look at peripheral blood to study human lymphocytes but most can be found in specialized tissues called lymphoid tissues
-functionally divided into two types
1. primary (central)
2. secondary (peripheral)
primary (central) lymphoid tissue
are when lymphocytes develop and mature in the bone marrow and thymus
secondary (peripheral) lymphoid tissue
-lymphoid tissues other than bone marrow or thymus
-lymph nodes
-GALT (gut-associated lymphoid tissue)
-BALT (bronchial-associated)
-MALT (mucosa-associated)
- spleen
Examples of secondary lymphoid tissue found in gut
-most secondary lymphoid tissue is associated with the gut (GALT)
-Tonsils
-Adenoids
-Appendix
-Peyer’s patches
lymphocyte recirculation
-the movement of lymphocytes are unique among blood cells in that they travel between the blood and a specialized network of lymphatic vessels (LYMPHATICS)
-most cells in peripheral blood are inactivated, the minute it becomes activated it moves through the lymphatics to a site of inflamation or lymph node
lymph nodes
lie at the junction between the lymphatics and the blood
Where is the adaptive immune response initiated?
-secondary lymphoid tissue (lymph node, peyer’s patches, spleen)
Draining lymph node
-the lymph node receiving the fluid collected at an infected site
Path of a draining lymph node
- pathogen components, dendritic cells in the afferent (acquire) lymph draining the site of the infection
- once in lymph node the dendritic cells take up residence and begin stimulating T-cells and B-cells, thus initiating the adaptive immune response
3 once clonal selection and expansion has occurred; mature, activated effector lymphocytes leave the lymph node through the efferent (exit) lymphatics
What does the spleen serve?
- filter the blood
- defense against blood borne pathogens
white pulp
similar in structure and function to lymph nodes
-found in the spleen
Peyer’s patch
-example of a organized GALT which is located in the regions of the small intestine
-specialized M cells sample the environment of the GI lumen for potential pathogens
leukocytes
any cell in the immune system
germinal centers
where the cells are growing
sinuses
where the arterioles and veniules come in and where affernt and efferent ducts are located