Immunology 2 BUSE

7/29/2019 Immunology 2 BUSE

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T Cells

Tc cells are CD8+, Th cells are CD4+

CD = cluster of differentiation

Expressed by various cells at particularstages of differentiation


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T Cell Receptors

Similar to Abs

Contain constant & variable regions

Mediate Ag recognition

Found on cell surface of T cell, but is not

secreted


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Major Histocompatability

complex T cells cannot recognize Ag alone

Ag must be presented in conjunction with

major histocompatability complex (MHC)

proteins

In humans called human leucocyte antigens


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MHC proteins are glycoproteins found on

cell surface

Vary from 1 individual to another & serve

as a label

2 classes, MHC I & MHC II are involved in

Ag processing Differ in structure, location & function


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MHC Ifound on all nucleated cells

Important in in presenting endogenous Ag,

eg virus to Tc cells

Endogenous Ags - produced within cytosol,

eg viral proteins in an infected cell


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MHC IIfound only on immunocompetent

celss such as macrophages & B cells

Present exogenous Ag to Th cells

Exogenous Agtaken up by endocytosis,

found in vesicles within cells

Eg bacteria & their products taken up by

macrophages


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Generation of Ab Diversity

Vast range of Ab-producing cells

exist, independent of exposure to any

specific Ag

Presence of a given Ag stimulates

production of a particular Ab or set of Abs


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Vaccination

Primary & Secondary Immune Responses

o

Following initial stimulation of a responseby particular Ag, memory cells specific to

that Ag are formed


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o On 2nd encounter response is faster &

stronger

-Memory cells are activated by Ag

-Become Ab secreting plasma cells

-Form further memory cells

o Basis of vaccination


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Principle of Vaccination

Non-pathogenic organism primes the

immune system so that on encounter with

pathogen, a protective response is generated


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During 1o challenge, stimulated B & T cells

proliferate & differentiate to give effector

cells + memory cells

Memory cells are long-lived & proliferatemore rapidly

o Facilitate rapid control of subsequent

infections


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Passive Immunization

Preformed Abs are transferred torecipient, eg.

o Natural maternal Abs

o

Artificial immune serum such as horseantivenin

Protects against snake biteShort-term protection


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Active Immunization

Protective immunity & immunologicmemory are elicited, eg.

o Natural infection such as flu virus

o Artificial infection such as vaccines-Attenuated organisms

-Inactivated organisms


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Route of Administration of Ag

Influences type if immune response

1. Systemic Response

Vaccine is introduced by injection

Increase of circulating Abs & specific T

cells

2. Mucosal Response

Vaccine is introduced orally or byrespiratory route

IgA predominates


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Uses of Adjuvants

Certain substances, which when

administered simultaneously with a specific

Ag, will enhance the immune response to

that Ag

Eg Aluminium Salts (hydroxyl, phosphates)

-1st safe & effective cpds to be used in

human vaccines

-Promote good Ab response, but poor CMI


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Attributes of a Good Vaccine

1. Ability to elicit the appropriate immune

response for a particular pathogen-Tuberculosis- CMI

-Most bacterial & viral infections- Abs

2. Long-term protection

-Ideally single dose-life long immunity


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3. Safety

-Non-pathogenic

-No side effects

4. Stable

-Should maintain immunogenicity

o Despite adverse conditions prior to

administration

5. Cheap


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Vaccine Production

In developing a vaccine, consider the branchof immune system to be activated


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Humoral immunity

o epitopes must be accessible to B-cell

receptors

o represent immunodominant epitopes

of infectious agent


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CMI

o vaccine should be capable of

maximizing presentation of Ag with Class I

MHC molecules

o Must undergo transient growth in

recipient


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Live Attenuated Organisms

-Virulence artificially reduced by in vitro

culture

i. Under adverse conditions, eg low To

ii. Selection of mutants which

replicate poorly in human host

-Often single dose reqd


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Replication of vaccine strain in host

i. Reproduces many features of w.t infection

ii Does not cause clinical disease

-Induces both humoral & CMI

Long-lived

-May revert to virulent form

Eg. Bacillus Calmette-Guerin (BCG)-an attenuated

Mycobacterium bovis (Tuberculosis)

-Viral particles causing measles or mumps


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Inactivated (Killed) Organisms

Virulent pathogen inactivated by:

o Irradiation with gamma rayso Chemicals such as formaldehyde orb-propiolactone

Produces mainly humoral immunity

o Poor immunogenicity

Requires multiple boosters

o Short-lived


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More stable

o Organisms need not be viable

o

Can withstand adverse storage conditions

Cannot revert to virulent form

o Safer

o Cannot replicate in host & cause disease

Eg.

o Cholera (bacterial)

o Influenza (viral)


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HIV Vaccine?

Problems

High mutation rate of HIV

Need for both CMI & humoral immunity

Lack of good animal model


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Trial Vaccines

Recombinant peptides, gp120

DNA vaccines

Live attenuated virus??


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Immunochemical Techniques

Techniques that use the interaction between

antibody (Ab) and antigen (Ag) to detect or

quantitate either Ab or Ag.


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Ab-Ag interaction is specific

-Ab to HIV reacts with HIV but not with flu virus

Examples

Anti-insulin Abs are used to quantify the amount

insulin in a serum sample

Bovine serum albumin (BSA) is used to test for

the presence of anti-BSA Abs in a rabbitimmunized with BSA


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Enzyme linked immunosorbent assay

(ELISA)

Detection reagent is an enzyme, which

converts a colourless substrate to coloured

product

Detected by simple eye or read by a

colorimeter

Can be used to assay for Ab or ag, can label

either Ab or Ag


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Assay Design

Many different variations on assay design

Solid phase for assay is usually a 96-well

microtitre plate which binds protein non-

specifically

Enzymes used mainly HRP or AP, which act on

a wide range of colourless substrates to givecoloured products

Small, do not interfere with Ab-Ag interaction


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ELISA for Ab to HIV

Coat plate with Ag

Block surface

Add serum sample

Add E-labelled anti-human Ab

Add colourless substrate


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Situations where Ab detection is inappropriate

Window period

Newborn with HIV+ mother

Solution Detect virus rather than immune response

eg PCR to detect viral RNA

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Immunology 2 BUSE