Molecular Bio

how was immunology discovered

edward jenner observed that milkmaids that got cow pox never got small pox even with close proximity to the virus

cow pox symptoms were much more mild so he injected material from a fresh cow pox vesicle into James Phipps

6 weeks later, Phipps was inoculated with small pox but never developed the disease

what are the big two types of immune responses

• innate or non-acquired response

• acquired or adaptive response

what two lines of defense are nonspecific 

• first line of defense

  • skin

  • mucous membranes

  • secretions of skin and membranes

• second line of defense

  • phagocytic white blood cells

  • antimicrobial proteins

  • inflammatory response

what line of defense is specific 

third line of defense

• lymphocytes

• antibodies

what are examples of anatomical and physiological barriers

• intact skin

• ciliary clearance

• low stomach pH

• lysozyme in tears and saliva

what are involved in cellular innate immunity

• natural killer cells

• neutrophils

• eosinophils

• mast cells

• macrophages

• dendritic cells

what are involved in humoral innate immunity

• complement 

• mannose binding lectin 

• antimicrobial peptides 

• LPS binding protein 

• C-reactive protein 

what is involved in cellular adaptive immunity

T cells and B cells

what is involved in humoral adaptive immunity

antibodies

characteristics of innate immune response

• non-specific and fast

• doesn’t improve with subsequent exposures

• first line of defense 

• 4 components

  • physical barriers

  • physiological barriers

  • vascular system

  • phagocytic component

what are some examples of physical barriers 

• tightly packed together epithelial cells

• keratin in skin = waterproofing

• epithelial shedding 

• mucous coat

what are examples of physiological barriers 

• fever - less microbial replication 

• low ph - less microbes 

• coughing/sneezing

• blinking 

• commensals

• antimicrobial molecules

• interferon alpha/beta - decreases infections in neighboring cells 

role of interferons

• released from virus-infected cells

• IFN binds to surface receptors on neighbor cells

• inducing uninfected cells to synthesize antiviral proteins that interfere with or inhibit viral replication

what are interleukins

a type of cytokine

soluble molecules that mediate interactions between cells

role of IL-1 and IL-6

induces fever and increases immune response 

role of IL-8

chemotaxis for neutrophil recruitment

role of IL-2

stimulates lymphocyte proliferation

role of lysozyme 

• found in tears, saliva, in granules of neutrophils 

• degrades bacterial peptidoglycan cell wall 

• bacteria succumbs to osmotic gradient and dies 

role of the vascular/phagocytic response

• acute inflammatory response upon penetration

• increases vascular permeability

• immune cells recruited from blood to remove invading pathogens

general function of complement 

• trigger inflammation 

• immune cell recruitment 

• coats pathogens to increase phagocytosis 

• kills pathogens 

components of the complement response

• 9 proteins that are broken down to form pore in pathogen that leads to death

• 3 pathways can lead to complement activation

  • classical pathway

  • lectin pathway

  • alternative pathway

what happens in the classical pathway 

• antibody mediated 

• C1 binds to Fc portion of IgG or IgM which starts cascade 

• splits C2 and C4 to form C3 convertase (C4bC2a)

• C3b is opsonized

• ultimately leads to C5 convertase 

what are the active fragments of the complement

C3a and C5a

role of C3a

• induce release of histamine by mast cells

• attracts neutrophils

role of C5a

• induce release of histamine by mast cells

• attracts neutrophils 

• strongly chemotactic for leukocytes and increases their adhesion to endothelial cells 

how does the complement cause lysis

• targets lysis by MAC
  metabolism and osmotic balance of target is disrupted

• DNA and protein synthesis stops

• fluids enter and target swells and bursts

what are the types of opsonins

C3b and antibodies

bind to foreign molecules

what are IgG antibodies and C3b recognized by 

IgG recognized by Fc receptors on immune cells 

C3b recognized by C3b receptor on immune cells 

what parts of a microbe are recognized by pathogen associated molecular patterns (PAMP)

LPS and flagellin

what are some types of pattern recognition receptors

• mannose receptors: sugars on pathogens → phagocytosis

• CD14

• toll-like receptors

role of toll-like receptors

• stimulates production of cytokines, chemokines, and antimicrobial peptides

• acts as pattern recognition receptor

• alert immune system of infection

• kills pathogens

what cells are part of the immune response

• granulocytes

• platelets

• mononuclear cells

• dendritic cells

• lymphocytes

where are all cells of the immune response derived from 

haematopoeitic stem cell (bone marrow) 

what regulates the production of cells of the immune response

colony stimulating factors

what does IL-7 regulate

lymphoid cells (T cells, B cells, and NK cells)

dendritic cell lineage

what does IL-3 regulate 

common lymphoid progenitor and haemopoietic stem cell 

what does granulocyte-monocyte CSF (GM-CSF) regulate 

along with granulocyte CSF, helps to regulate production of granulocytes 

• mast cells

• basophils

• neutrophils 

• eosinophils 

what does monocyte CSF regulate 

monocytes → macrophages 

what does granulocyte CSF regulate

along with GM-CSF, regulates granulocytes

• eosinophils

• neutrophils

• basophils

• mast cells

what are the types of granulocytes

• neutrophils

• eosinophils

• basophils

• mast cells

general features of granulocytes 

• produced in bone marrow 

• 50 billion in circulations 

• release contents of cytoplasmic granules to kill pathogens 

what granulocyte arrives first to the scene of the immune response 

neutrophils 

what are the general features of neutrophils

• 95% of circulating granulocytes

• multilobes nucleus

• aka polymorphonuclear neutrophils

• migrate rapidly to site of infection

• phagocytose and destroy foreign organisms

• produce myeloperoxidase and lysozyme

what makes up the majority of circulating granulocytes

neutrophils - 95% of circulating granulocytes

function of neutrophils

• produce myeloperoxidase and lysozyme

• phagocytose and destroy foreign organisms

• release reactive oxygen species and phagolysosome enzymes to kill pathogens

what receptors do neutrophils have to aid in pathogen detection

• Fc receptor

• complement receptors

• toll-like receptors

defining physical characteristic of neutrophils 

multilobed nucleus

stains purple

defining physical characteristic of eosinophils 

• bilobed nucleus 

• stains pink with eosin 

what is the main function of eosinophils

• bind to Ig coated parasites

• release granules to kill helminths

• involved in allergies and produces histamine/pro-inflammatory molecules

where do most eosinophils reside 

connective tissue 

frequency of eosinophils 

makes up 2-5% of white blood cells

frequency of basophils

0.2% of white blood cells

where do most basophils reside 

in blood stream 

same function as mast cells, but those are in the tissue

physical characteristics of basophils 

• hard to see nucleus

• lots of molecules

• stains blue with hematoxylin 

function of basophils

• release histamine and inflammatory molecules

• allergen must cross link IgE molecules bound to its surface

• often linked to hypersensitivity reactions

function of mast cells 

release histamines when allergen is encountered 

• mucosal mast cell 

• connective tissue mast cell 

function of platelets aka thrombocytes

• blood clotting 

• involved in inflammation 

• adhere to endothelial surface of damaged blood vessel and release factors to:

  • modulate capillary permeability

  • leukocyte recruitment

what are macrophages derived from

monocytes in blood and become macrophages in tissue

defining physical characteristics of mononuclear phagocytes

• largest in size of circulating WBCs

• horseshoe shaped nucleus

frequency of mononuclear phagocytes

2-8%

naming convention of mononuclear phagocytes

• names vary on location

• ex. kupffer cells in liver

• microglia in brain

function of mononuclear phagocytes

• innate immune response

  • phagocytosis

  • release chemoattractive factors for other immune cells to boost immune response

  • release leukotrienes and prostaglandins to increase vascular permeability/cell recruitment

• assist acquire immune response

  • a type of antigen presenting cell

  • present antigen to T cells

how do macrophages assist the acquired immune response 

• when macrophage digests a pathogen, some antigen is saved on the MHC (major histocompatibility complex) 

• APC to secondary lymphoid tissue activates T cell that recognizes antigen to generate immune response 

where are MHC class I molecules located

on all nucleated cells

where are MHC class I and II molecules located

on antigen presenting cells (APCs)

aka macrophages, dendritic cells, B cells

what is a normal MHC filled with 

self protein 

what is an MHC filled with in the case of infection

filled with antigen from invading organism

definition of antigen

immunogen

something that induces immune response

definition of epitope

3D molecular arrangement on antigen recognized by immune system 

definition of hapten

too small for immune response unless attached to larger molecule

what makes up MHC I

• 3 alpha chains

• 1 beta microglobulin

what makes up MHC II 

• 2 alpha chains 

• 2 beta chain

specific T cell will recognize foreign antigen in MHC II molecule and stimulate immune response 

where are class II and class I molecules located on chromosomes

• short arm of chromosome 6

• HLA region is most polymorphic gene cluster of entire human genome

where do dendritic cells reside

in most tissue and organs

function of dendritic cells 

• professional antigen presenting cells

• capture, process, and present antigens to T-cells to initiate adaptive immune response

function of lymphocytes 

• specificity and memory function of acquired immune response

• have antigen receptor that recognizes one specific epitope 

• once programmed, cannot be changed 

how much of total lymphoid cells do B cells make up

5-15% of B cells

function of B cells 

humoral response

binds to antigens in bodily fluids 

have antibodies on their cell surface to recognize foreign antigens 

characteristics of B cell antigen receptor

• membrane-bound antibody receptor

• unique antigen-binding site

• once bound, antigen is internalized and processed to be presented to helper T cells

steps of B cell activation

1. B cell finds antigen which matches its receptors

2. it waits until it’s activated by a T helper cell

3. B-cell the divides to produce plasma and memory cells

4. plasma cells produce antibodies that attach to current type of invader

what is clonal selection 

each lymphocyte is specific to a particular antigen 

what is clonal expansion

production of daughter cells that share the same antigen specificity

what are the two types of cells produced by B cells

• plasma cells

• memory cells

characteristics of plasma cells 

• live only a few days 

• secrete antibody that bind the same epitope (specificity) 

characteristics of memory cells 

• persist in circulation for a long time 

• persist even longer if they encounter the same antigen

what is the primary response to an antigen

• first exposure to antigen

• lag phase: lasts days to weeks

• IgM first produced

what is the secondary response to an antigen

• second exposure to antigen

• shorter lag phase

• more antibody produced

• IgG > IgM

what determines the isotype of an antibody

amino acids of heavy constant chain 

what are the two components of an antigen binding site

variable end of heavy chain + variable end of light chain

how are antibodies cleaved

enzyme breaks disulfide linkages in hinge area to separate Fc and Fab regions

what is the Fab region

• antigen binding fragment 

• each arm is an antigen binding region 

what is the Fc region 

• interacts with:

  • complement

  • immune cells

    • neutrophils

    • macrophages

    • other phagocytes

structure of an antibody 

• 2 identical heavy and light chains 

• constant and variable end regions

• isotypes: IgG, IgA, IgM, IgE, IgD

what is the most abundant antibody in serum

IgG (70-75%)

how many subclasses does IgG have 

four - IgG 1 to IgG 4 

which antibody has the highest half life

IgG - 3 weeks

characteristics of IgG

• main antibody in secondary response

• passes through placenta for neonate immunity

• activates complement

• antibody-dependent cell mediated cytotoxicity

what is the abundance of IgA

15-20% 

major antibody present in mucous secretions such as saliva, tears, breast milk in the form of dimer called secretory IgA

what is the half-life of IgA

6 days

characteristics of IgA

• two forms - IgA1 and IgA2

• monomeric in circulation

• associated with another protein called secretory component