Tolerance Specific negative immunity Not the same as immunosuppression, which is non-specific 3 Tolerance mechanisms: Clonal deletion: Loss of certain.

Tolerance

Specific negative immunity

Not the same as immunosuppression, which is non-specific

3 Tolerance mechanisms:

Clonal deletion: Loss of certain Ag-specific cells

Clonal anergy: clone is present, but unable to respond

May be slowly reversible

Clonal suppression:

Response re-appears if suppression is removed

Occurs in primary lympoid tissues

Clonal Deletion (negative selection)

For T cells, occurs in thymusIrreversible loss of activity, since Ag-reactive cells are gone

Negative selection can be studied observing V17 T cell receptor model

V17 is never expressed on peripheral T cells in mice that have MHC II IE

V17 is expressed on cortical thymocytes

Lost on mature thymocytes due to negative selection

% cells with V17a:Cell Population: SJL (IE-) B10.BR (IE+)

Immature ( 4thymos CD+8+) 2.9 2.6 Maturethymos

( 4+)CD 2.4 0.06( 8+)CD 0.4 0.01

Periph T cells 13.9 0.09

Thymocytes expressing TCRs bearing V17 bind too strongly to a conserved regionof IEa or IE. This causes inappropriate signaling, and cells are deleted

Where does negative selection occur?Positive selection occurs on thymic epithelium

Tested cells responsible for negative selection using bone marrow chimeras

Bone marrow from various donors was transferred into irradiated recipients

Marrow donor Recipient(thym epith)

% periph T cellsV17a+

IE- IE- 13.6

IE+ IE- 0.1

IE- IE+ 16.2

IE+ IE+ 0.08

Bone marrow cells from donor determine negative selection

Host DC die from irradiationReplaced by DC from donor marrow

Positive selection is on host thymic epithelium

Negative selection occurs on donor-derived DC

How is Reactivity to non-Thymic Self Ags Prevented?Clonal anergySuppression

Clonal Anergy

Ag signals T cell in an improper fashionCell is turned off rather than on

Seen when cell gets signal 1 (TCR) but not signal 2 (co-stimulation)

Neonatal thymectomy freezes the early situation, see V6 in periphery

During the first week of life, autoreactive T cells are released from thymus

As mouse ages, negative selection initiates, and this process stops

Thymectomize

Normal Adult

V

B

6 gradually disappears

from LN, Spleen

Day 0-4

B

V 6 moving out

to LN, Spleen

Adult w/day 3 thymectomy

freezes d.3 picture

V 6 remains in periph

B

DBA/2 mouse: T cells with Vb6 TCR autoreact with IEd

NTx mouseAdult mouse: (%V6) Neonatal mouse: (as adult)Cortex Medulla Periph Cortex Medulla Periphery Periphery

3.1 0.2 0.1 3.6 3.2 3.3 3.2

Cells: Prolif IL-2 prod V6 freqcy

Adult med +/- +/- 0.2% neg ; sel'd no fn left

3 Day med ++++ ++++ 3.6% not neg ; sel'd fn remains Adult periph +/- +/- 0.2% neg sel'd

NTx periph +/- +/- 3.3% not neg ; !sel'd anergic

Peripheral cells have been anergized

Day 3 thymocytes can respond to IEd however peripheral cells in the thymectomized mouse cannot

Adult medullary thymocytes

Day 3 medullary thymocytes

Adult peripheral T cells

Neo-thymectomized T cells

Measure: IL-2 production

Proliferation

IE Plate

d

IEd APCs

CD28/B7 is the most commonForm of co-stimulation

IL-1 can Co-stimulate TH2 cells

CD28/B7 is most commonStimulator for CD8 cells

Clonal deletion occurs in B cells

Tgenic mouse #1genes for H&L chains

anti-K Abb

Tgenic mouse #2genes for H&L chains

anti-K Abb

1. Normal level of B cellsin BM, L, Spleen

2. >95% display Tgenic sIg

1. No B cells in Ln, BM, Spleen

2. Clonal deletion and tolerance

H - 2b

H - 2k

B cells eliminated if specific for cell surface self Ag seen in BM

Peripheral deletion of B cells

H-2

k

H-2

k

Tgenic mouse #1 Tgenic mouse #3

X

F-1

gene for k

b

under liver promoter

1. In adults- normal levels of B cells in BM

>95% display Tgenic sIg

2. almost no B cells in LN, Spleen

none display Tgenic sIg

3. Clonal deletion (peripheral tolerance)

B cells also eliminated if see self cell surface marker in peripheryNot deleted in BM, deleted in periphery

This is linked to failure to activate CD4 helpCD40 on B cell must be ligated by CD40L on activated T cell, or B cell dies

B cell tolerance to soluble self Ag

Tgenic mouse #1

genes for H&L chains

of anti-HEL Ab

1. >95% B cells have Tgenic sIG

2. Normal B cell levels, LN, Spl

3. Normal mu, delta chains

x

Tgenic mouse #2

gene for HEL

1. makes, secretes HEL

2. Tolerant to HEL

a. T cells

b. B cells

F-1

1. Makes, secretes HEL

2. Normal B cell levels- BM,LN,Spl

3. B cells are mu low, delta hi

>95% have Tgenic sIg

4. B cells are anergic

cannot respond to HEL

Transfer B cells

to normal mouse

Normal Mouse

1. B cells home to LN, Spl

2. inject hi [HEL]: become anergic

Altered levels of mu, delta chains

High levels of soluble self Ag cause alterations of B cell phenotype

B cells are not deleted, become low, high…..Anergized

Suppression as a Tolerance Mechanism

Some CD4 T cells are now thought to suppress immune responsesThese T regulatory cells are:

CD25+ (High affinity IL-2 R)CTLA4+Express IL-10, TGF-

APC

CD4+CD25+

MHC/Peptide

CTLA-4CD80/CD86

immunosuppressivecytokinesIL-10TGF-

TCR

4+ CD Treg Cells

Activation of the Treg cell is Ag specificSuppression by the Treg cell is non-specificIf Treg cells are removed, Ag-reactivity ensues

T regs may be involved inPeripheral tolerance to a Variety of Ags

To Initiate a Proper Immune Response

3 signals are required:

1. TCR/Ag binding2. Co-stimulatory signal

3. Trauma or stress (danger signal) from injured cells/tissuesActivates APCsInitiates inflammation

Autoimmunity

Organ specific disease

Systemic disease

Response targets a unique organ or glandDirect cellular damage occursFunction of tissue stimulated or blocked by Abs

Response directed against a broad range of AgsInvolves multiple organs or tissues

Organ Specific Autoimmune Diseases

Hashimoto’s ThyroiditisDTH response to thyroid AgsInflammatory response causes goiter (enlarged thyroid)

Pernicious AnemiaAbs to membrane-bound intestinal protein (intrinsic factor) Block absorption of vitamin B12Hematopoiesis altered

Autoimmune Hemolytic Anemia

AutoAb to RBC proteins complement lyses RBC

Insulin-Dependent Diabetes Mellitis

DTH and autoAbs against islet cells in pancreasCytokines and lytic enzymes from macrophages destroy islet cells insulin production reduced

Graves Disease

AutoAbs to thyroid stimulating hormone R mimics receptor signaling thyroid hormones produced

Myesthenia Gravis

Blocking Abs to acetylcholine R inhibits muscle activation C’ mediated destruction of receptor

Systemic Autoimmune Diseases

Multiple SclerosisT cells reactive to myelin basic proteinNumerous neurologic malfunctions

Systemic Lupus Erythematosis (SLE)Multiple autoAbs (DNA, histones, RBC, platelets, clotting factorsImmune complexes deposited, destroy blood vessel wallsRBCs lysed, kidney damageOften see butterfly rash on face, sun sensitivity

Rheumatoid ArthritisChronic inflammation of jointsHematologic, cardiovascular and respiratory systems affectedRheumatoid factors (anti-IgG Fc) cause immune complexes localize to joints, activate C’, inflammation

Ankylosing SpondylitisAssociated with HLA-B27Destruction of large jointsFusion of vertebrae

Clinical Manifestations

of

Rheumatologic Diseases

(Tolerance Gone Awry)

Rheumatoid Arthritis

Rheumatoid Arthritis

Juvenile Onset RA: Growth Deformities

14 YOA, 3’9”RA left knee, increased bone length

SLE: Anti-Nuclear Ab

Systemic Lupus Erythematosis

Butterfly Rash Light Hypersensitivity

SLE: Kidney Damage

Immune complexes (pink) deposits onBasement membrane (black)

IgG deposits in glomerulus

Ankylosing Spondylitis

26 year time courseInvolvement in hips and knees

Bi-lateral hip replacement in 1973