MICR 386 Midterm

Thymus Bone Marrow

Adenoids Tonsils Bronchus-associated lymphoid Tissue Lymph nodes Spleen Intestines Peyer's patches appendix

physical barriers, chemical elements, immune cells

Nonspecific cellular responses

B and T cells 1st encounter: primary immune response. Develop memory cells aka acquired immunity

innate and adaptive systems detect any foreign/defective cells prevents proliferation of dangerous cells

microbes macromolecules cells

unchanging (continuous protection, without rearrangement/alterations to response)

immediate (occurs within minutes)

nonspecific reactivities (reaction can be to a common component on multiple pathogens, i.e., LPS)

Broad range of targets (anything foreign)

No memory

mucous membranes

cilia/hairs

epithelial barriers

secretions (tears, saliva, etc) commensal organisms (gut, vagina) spermine (semen) acidic pH of stomach

White blood cells derived from hematopoietic stem cells in bone marrow phagocytes and granulocytes

neutrophils, macrophages, dendritic cells

1st responding leukocyte function for inflammation increasing segmentation as they mature 50-70% of immune cells phagocyte AND granulocyte

most of professional phagocytes ingest old neutrophils, bacteria secrete cytokines stimulate inflammatioon, recruitment of immune cells link between innate and adaptive immune system 1-6% of all immune cells phagocyte

found on tissues in contact with external environment link between innate and adaptive immune systems ingest microbes phagocyte

eosinophils, basophils, mast cells, neutrophils

granulocyte secretes histamines activated by parasitic infection mediator of allergic reactions 1-3% of immune cells

granulocyte secrete heparin and histamine respond to parasitic and allergic reactions <1% of immune cells

role in allergy/anaphylaxis heparin and histamine rich granules protective role in wound healing, angiogenesis, blood-brain barrier <1% of immune cells

large, granular, cytotoxic lymphocytes do not have T or B cell Receptors do not require activation to kill cells antibody-independent Can interact with antibodies during antibody-dependent cell mediated cytotoxicity for fast immune response role in surveillance important for host-rejection of tumours/virally infected cells

complement Mannose-binding lectin C-reactive proteins coagulation factors

all are opsonins

mark pathogens for destruction (opsonization [phagocytosis] or cell lysis)

opsonization of microbes activation of complement

opsonization of microbes activation of complement acute phase proteins, secreted by hepatocytes in response to inflammation

activated by PAMPs opsonins act as attachment sites for receptors aiding in phagocytosis neutrophils form pus, macrophages form lysosomes

LPS Receptors Scavenger receptor mannose receptor N-formyl methionyl receptor

Lipopolysaccharide in gram negative bacteria LPS binds to LPS receptor, initiates inflammatory signalling cascade

family of receptors removal of foreign substances, waste materials bind to many ligands, including LDLs (low density lipoproteins)

only microbes acts as pattern recognition receptor can recognize several different microbes

bacteria create fMLP fMLP recruits inflammatory cells, i.e., neutrophils

unenhanced enhanced

initiate phagocytosis upon attachment attachment via LPS, scavenger, mannose, N-formyl-methionyl nonspecific innate recognition of PAMPs through pattern recognition receptors

do not initiate phagocytosis upon attachment attachment via opsonized microbe to phagocyte occurs via IgG antibodies, complement proteins, acute phase proteins (mannose-binding lectin), C-reactive proteins

attachment ingestion fusion digestion release

pseudopods engulf microbe microbe put in endocytic vesicle (phagosome) pH lowered to 4

phagocyte lysosomes travel along microtubules, fuse with phagosomes create phagolysosomes

microbe broken down by lysosomal enzymes in phagolysosomes ROIs and iNOS creates oxidative environment, damaging biological molecules

indigestible materials in vesicles are called residual bodies released via exocytosis, or displayed via MHC-antigen complexes

Discrimination (can discriminate between self and non-self)

diversity (responds to variety of microbes/molecules)

specificity (capable of distinguishing subtle differences in foreign antigens

specialization (immune response is antigen-dependent, ensures optimal defence. Lag time of 4-5 days.)

memory (enhanced response to microbe following repeated exposure)

self-limitation (microbe-activated immune responses can return to basal state once microbe is eliminated)

Plasma B cell (mature B cell, secrete antibodies)

Memory B cell (express cell-surface antibody isotopes IgM and IgD, involved in secondary antibody response)

Helper T cell (regulatory, may activate macrophages or induce antibody production by B cells)

Cytotoxic T cell (effector cells, kills targets)

humoral immunity

plasma cells secrete antibodies

contain B7 and CD40 on surface

express IgM

express IgM and IgD

CD4+ regulatory, maintain/suppress immune cells/reactions

2 classes

• Th1: activate macrophages, cell-mediated immunity

• Th2: induce B cells to differentiate into plasma cells and produce antibodies

require serial triggery (many TCRs interact with many MHC)

takes longer to initiate

release cytokines, which active macrophages, T and B cells

inflammatory response

humoral response

CD8+ Effector cells short lived kill target cells activated by just one MHC-antigen complex release cytotoxins, creating holes in APCs and lead to cell death

cell mediated response

Required to activate T cells Phagocytose antigen, bind it to MHC, display MHC-antigen complex on cell membrane

Express MHC Class I and II Dendritic cells, B cells, macrophages activate helper T cells (via serial activation) and cytotoxic T cells (one activation only)

all nucleated cells only express MHC Class I only activate cytotoxic T cells

found in mucous membranes neutralizing antibody prevents attachment of pathogen to mucosal epithelium present in colostrum does not activate complement responsible for antimicrobial activity in secretions alpha (a) heavy chain

IgA1 = T shaped (has hinge region), found in aerodigestive tract IgA2 = Y shaped (lacks hinge region, light chain non-covalently bound to heavy chain), found in large intestine

small amounts in blood no known effetcs expressed on surface of mature B cells that have not been exposed to antigen, along with IgM Not expressed on immature B cells Delta (s) heavy chain has hinge region

lungs, skin, mucosa role in anaphylaxis through release of histamine from granulocytes protects against parasitic infection Epsilon (e) heavy chain no hinge region binds Fc receptors on mast cells and basophils low levels 4 e constant domains

dominant immunoglobulin in immune response activates complement when bound to antigen binds Fc receptors of cells Found in all bodily fluids fights bacteria and viruses can cross placenta gamma (y) heavy chain

largest antibody found in blood and lymph, mostly confined to bloodstream found on mature B cells fight new microbial infection activates complement very well Mu (u) heavy chain pentamer, joined by disulphide bond and a J chain responsible for blood type cross-links antigen well lacks hinge region

Molecule with ability to evoke a specific immune response, and can react with the resultant specific antibody

Always an antigen Always elicits an immune response

molecule that can react specifically with either a preformed antibody, immunoglobulin receptors on B cells, or T cells

not always an immunogen, since not all antigens elicit an immune response

Foreignness: greater genetic difference = better immune response

Molecular size: larger molecule = greater immune response. >10,000 Da are good immunogens

Molecular complexity: greater internal molecular complexity = better immune response (single aa = :(, addition of aromatics = :), since stabilize structure)

Degradability: easy phagocytosing = more immunogenic

Physical form: particulates more immunogenic than soluble (since particulates aggregate), denatured more immunogenic than native (more exposed peptide)

small organic molecule that is antigenic, but not immunogenic unless attached to carrier protein

used to solicit immune response

i.e., hapten alone: no immune response, too small. Carrier alone: no immunogenicity, so no immune response. Carrier-hapten conjugate: immune response

complication = penicillin, since it can form a covalent bond with endogenous proteins, making a conjugate that can mount an immune response

substance that enhances immunogenicity when injected into a human, without resulting in the mounting of an immune response against it

do not induce immune responses alone

keep antigen localized to tissue, prevent dispersion throughout body

basic principle of vaccine development, commonly used in vaccines

enhance inflammation/development of immune response

activate APCs to digest/present antigen on MHC II molecules

immunologically active region of antigen

region that binds to T or B cell receptors or to antibodies

soluble antibodies bind to epitopes of exogenous antigens using non-covalent interactions

characteristics: complementary (lock and key) shape at binding site. Flat/undulating interacting surface

antibodies can recognize epitopes that are sequential (linear) or non-sequential (discontinuous, but in adjacent regions due to secondary or tertiary structure)

B cell receptors recognize exogenous antigens epitopes can be sequential or non-sequential

multivalency (antigens with multiple epitopes can be recognized by antibodies)

• homogenous multivalent antigens (contain same epitope, repeated multiple times. Results in one type of immune response)

• heterogenous multivalent antigens (express different epitopes, results in variety of immune responses)

Immunodominance (some epitopes will be dominant over others. Determined by accessibility of epitope, specificity to binding site, and affinity of epitope to B cell receptor)

specificity (antibody can discriminate between antigens, and have higher affinity for one over another)

• acidic groups: contribute to specificity

• glycoside groups: infer extreme antibody specificity

Accessibility: if antibody cannot reach epitope, no immune response is elicited

recognize antigens via T cell receptors antigens then processed, presented on MHC molecules to T cell receptor by APCs after phagocytosis, proteins degraded into small, linear peptides, which then bind to MHC, and recognized by T cell receptor

interacts via antigen + Ig

can bind soluble protein

does not require MHC

epitope properties: accessible, hydrophilic, peptides are sequential or non-sequential

T cell receptor + antigen + MHC

cannot bind soluble antigen, requires MHC

epitope properties: internal linear peptides, produced by antigen processing, then bound to MHC

combinations of disease (TB infection + HIV = disease)

improper antibiotic use (antibiotic resistance, results in MRSA, MDR TB)

laxity in vaccination adherence (less immunization = no herd immunity)

humoral or cell-mediated immunity and memory

follows exposure to antigen

natural or artificial

following exposure to infectious disease

individual produces antibodies, recovers from infection, long term immunity

natural infection (i.e., from community)

following immunization via vaccine long-lasting protection recipient not usually infected with infectious agent

external antibodies, giving immediate, short lived protection

transfer of maternal antibody across placenta, providing immunity to fetus

concentrated immunoglobulin fraction extracted from serum of immune individuals, and injected to protect susceptible individuals

effective, long lasting immunity safe, easy to administer no adverse reactions no reversion to virulent forms stable available worldwide, inexpensive

Live attenuated I: infect animal cell culture, virus replicates in animal cells many times, virus gets mutations diminishing specificity to human cells

Live attenuated II: genetically engineering the virulent gene of virus so it is mutated or deleted

Pros: excellent immune response

Cons: less safe, can revert to virulent form

killed by physical/chemical processes non-functional, but antigen is intact, so can elicit immune response

pros: no live components, so very stable and safe

cons: weaker immune response, may require multiple doses

inactivate bacterial toxin so it cannot cause disease, but an immune response is mounted

Pros: cannot cause disease, cannot revert to virulent form, stable and long lasting

cons: not highly immunogenic, requires several doses

consist of antigenic component of pathogen i.e., capsules, acellular, recombinant vaccines

pros: no live components, so no risk of disease introduction

cons: weaker immune response, must determine which combo of antigens will give a good immune response. No guarantee of memory for future infection

different types of influenza infect a single cell

HA and NA proteins can be traded, resulting in a new strain of influenza, and therefore prevention of immunity

rapid and drastic change of antigenic shift results in little to no resistance against new combination of HA/NA proteins

virus accumulates point mutations in genome, altering structure enough that adaptive immune system does not recognize HA/NA proteins

responsible for changing flu vaccine formulation annually

Antigen binding: Bind specifically to antigens Mediate effector functions; elicit biological responses

Monoclonal (derived from a single B cell, specific for single epitope)

Polyclonal (heterogenous mix of antibodies with different affinities, produced by many clones of B cells. Recognize multiple epitopes)

determines if an antibody is present in a blood sample through analysis of antiserum (serum containing antibodies)

2x heavy chains 2x light chains interchain disulphide bonds (hold heavy and light chains together) interchain disulfide bonds (between polypeptide chains) Variable region Fab region (antigen binding fragment) Fc region (crystallizable fragment) constant region hinge region (not in IgM or IgE), provides flexibility domains oligosaccharides hypervariable region (infers variability, aka complementarity determining region)

Papain

• cleaves Fc from Fab just below hinge region

Pepsin

• cleaves entire Fc region up to hinge region. Leaves F(ab')2 region only

phenotypic variations in constant regions

define immunoglobulin class (i.e., IgG, IgA, etc.). Immunoglobulin class determined by heavy chain isotope 5 heavy chain isotopes (y, a, u, e, s) 3 light chain isotopes (k, lambda)

Allelic variation occurs in constant heavy and light chain regions of one isotope

slight differences in aa sequences of heavy and light chains between individuals

found on IgG, IgA2 heavy chains, and k light chains

used for paternity testing

changes in variable region (antigen binding site) results in recognition of a specific antigenic epitope

cancer cells, cannot produce antibody, do not grow in HAT medium

fusion of myeloma cell with antigen-specific plasma B cell can produce antibodies, but have longevity from myeloma cells

can grow in HAT medium

VJ rearrangement

1- somatic recombination (V-J joining) 2- transcription, RNA splicing 3- PolyA tail added to 3' of Ck, mRNA exits nucleus, enters rough ER 4- L sequence pulls growing polypeptide into lumen of ER, then cleaved off 5- k light chain is glycosylated and processed

VDJ rearrangement

1- 1st rearrangement (D-J joining) 2- 2nd rearrangement (V-DJ joining) 3- transcription, RNA splicing 4- add polyA tail to 3' sites of Cu 5- L sequence pulls polypeptide into lumen of ER, and is cleaved off 6- processing/glycosylation of protein

conserved sequences of noncoding DNA functions as signals for recombination process found adjacent to the point where recombination occurs

• 3' end of each V segment

• 5' end of each J segment

• each end of D segments recognized by RAG1 and RAG2 during VDJ recombination contains

• conserved palindromic heptameter

• conserved AT rich nonuser sequence

• separated by 12 or 23 non-conserved base pairs (1 or 2 turns)

variable region has 2 turn RSS, junction region has 1 turn RSS

diversity region has 1 turn flanking 5' and 3' cannot have one turn/one turn, or two turn/two turn pattern must be one/two

one turn/two turn causes a loop to form, where RAG enzyme cuts excess gene segment therefore, 12 and 23 bp spacers are not conserved

Joining of VDJ segments in phase produces VJ or VDJ unit that can be translated 1 positive rearrangement in 1 allele is enough to make an immunoglobulin

gene segments joined out of phase triplet reading frame for translation is not preserved no immunoglobulin is made i.e., if reading frame gets shifted to code a stop codon

after VDJ rearrangement, heavy chain is polyadenylated

site of polyadenylation determines if the antibody will be membrane bound or secreted

immature developing B cells = polyA site 2 and 4, make membrane bound antibodies

plasma cells = polyA site 1 and 3, make secreted antibodies

Ig isotope switching changes the type of antibody produced occurs between switch (S) sites upstream of the heavy chain (except gamma)

creates dsDNA breaks at S sites. unwanted portion of heavy chain removed, and remaining segments re-joined by non-homologous end joining, to produce a different isotope

antigen specificity maintained, but the type of heavy chain changes, therefore Ig class changes

this changes which effector molecules the antibody will interact with

Can occur in P-region or N-region of DNA increases antibody diversity

occurs during rearrangement of gene segments in initial development of B cells

cleavage of hairpin requires addition of nucleotides, but the number added is random, disrupting the reading frame, causing mutations

cleavage of hairpin generates site for addition of P-nucleotides repair enzymes add complementary nucleotides make palindromic sequences added to ends of gene segments