11/4 Primary Immunodeficiencies + Allergies/Type I Hypersensitivity

Primary immunodeficiencies are…

immunodeficiencies that are heritable or develop in the womb

Cause of primary immunodeficiencies

Genetic

Targets, presence & severity, and pathology for primary immunodeficiencies

• categorized based on which cells (B or T cells) or processes (Innate vs. adaptive) are most greatly affected

• present early in life

• vary in severity

• increased bacterial & viral infections

What are the 3 methods for screening in newborn blood samples?

1. Look for high Ab levels

2. Look for high leukocyte count

3. Abnormal amount of TCR excision circles - pdt of TCR gene rearrangement

What are combined immunodeficiencies?

Variable immune defects of humoral and cell-mediated adaptive immunity

What is good to remember about combined immunodeficiencies (most often a…)

Most often a defect in 2+ things

What genes are affected by severe combined immunodeficiency (SCID)?

V(D)J / TCR genes including RAG 1/2, artemis, DNA-PK, CD3 and IL-7R

What does severe combined immunodeficiency target?

Early lymphocyte development, specifically within T cells

How does severe combined immunodeficiency affect reticular dysgenesis?

Defective differentiation of HSCs → myeloid + lymphoid lineages

How does severe combined immunodeficiency affect adenosine deaminase?

Defects in purine metabolism → no DNA/RNA synthesis

How does severe combined immunodeficiency affect RAG ½ and artemis?

V(D)J rearrangement defects

How does severe combined immunodeficiency affect T cell progenitor cells?

Defective cytokine signaling

What are the two general clinical outcomes of severe combined immunodeficiency?

• absent t cells

• diminished or absent B cells and NK cells

What gene is affected in bare lymphocyte syndrome - MHC I and what is that gene responsible for?

Mutation in transport associated protein (TAP) responsible for transporting self ag onto MHC I

What happens in bare lymphocyte syndrome - MHC I?

no export of MHC I to surface because no self Ag loading

What does MHC I/Self ag bind to in bare lymphocyte syndrome - MHC I and what does this cause?

CD8+ T cells and results in impaired positive selection of these cells

What is the general clinical outcome of bare lymphocyte syndrome - MHC I?

More susceptible to viral and bacterial infections

What is a key sign/symptom of bare lymphocyte syndrome - MHC I and what’s it caused by?

NK cell induced necrotizing skin lesions since NK cells attack cell due to no MHC I expression

What gene(s) are affected by bare lymphocyte syndrome - MHC II?

Mutation in transcription factors transcribing MHC II

What happens in bare lymphocyte syndrome - MHC II?

No presence of MHC class II molecules

• MHC II/foreign Ag binds to CD4+ T cells resulting in impaired positive selection of them

What is the general clinical outcome of bare lymphocyte syndrome - MHC II?

CD4+ cell defect → impaired peripheral T helper cell responses resulting in increased susceptibility to infection

What gene(s) are impacted by DiGeorge’s syndrome?

Deletion of regions on chromosome 22

• TBx1 gene (T-box1)

• Deletion of 30-40 genes with unknown function

What happens as a result of DiGeorge’s syndrome?

No t cells and low levels of B cells and Abs and an increased susceptibility to infection → no adaptive immune system

• no t cells → no t cell dependent activation of B cells → low ab count

What is the general clinical outcome of DiGeorge’s syndrome?

Developmental defects in thymus, facial features, and heart and learning impairments

What gene is impacted in Hyper IgM syndrome (X-linked)?

Deficiency in CD40L (recessive X-linked gene)

What is the function of CD40L?

Present on T cell which binds to CD40 on B cell → induces Ig class switching and important in activation

What happens during hyper IgM syndrome?

Impaired communication between CD4+ T cells and B cells

List the 3 steps/results of hyper IgM syndrome

1. Limited t dependent activation of B cells → low Abs

2. no b cell isotype switching → lots of (hyper) IgM

3. Less t cell activation & memory cells

What is the general (3) clinical outcome of hyper IgM syndrome?

• Frequent bacterial infections and diarrhea, failure to thrive

• Low neutrophil count

• autoimmunity

What gene is impacted by Wiskott-Aldrich syndrome (WAS, X linked)

Deficiency in WASP gene → codes for cytoskeletal protein found in all hematopoietic cells

What is impacted by wiskott-aldrich syndrome (3) (WAS, X-linked)

Defects in…

• cell migration

• actin polymerization

• signal transduction of WBCs

What is the general clinical outcome for wiskott-aldrich syndrome (and 5 symptoms)

Impaired Ab and cell-mediated immunity and symptoms:

• eczema

• thrombocytopenia (low platelet count) → bleeding

• recurrent bacterial infections

• B cell malignancy

• autoimmunity

What are B-Cell / Ab immunodeficiencies?

Depressed production of B cells and one or more Ab isotype

What gene is impacted by Hyper IgE syndrome (job syndrome) and what does it usually do?

Deficiency in STAT3 gene → binds to gamma interferon activation site → code for cytokine production (affects Ig class switching)

What is impacted as a result of Hyper IgE syndrome (job syndrome)

Dysregulation of Th cell pathway

• especially Th17 cells → low numbers

• high IgE levels

What is the general clinical outcome of hyper IgE syndrome (job syndrome)? (Name 4)

• High IgE levels

• eosinophilia (lots of eosinophils) & impaired humoral immunity

• facial abnormalities

• fragile bones (musculoskeletal, connective tissue, denial defects)

What gene is impacted by x-linked Agammaglobulinemia and what is it required for? (Bruton’s hypogammaglobulinemia)

Defect in Bruton’s tyrosine kinase → required for pre-BCR signal transduction after heavy chain

What happens as a result of x-linked Agammaglobulinemia?

Extremely low levels of Abs

• B cells remain locked in pro-B cell phase → do NOT proceed to pre-B

What is the general clinical outcome of x-linked Agammaglobulinemia?

Recurrent bacterial infections

What gene is affected by selective IgA deficiency?

Various B cell regulatory proteins in the constant region

What happens as a result of selective IgA deficiency?

IgA-secreting B cells can’t differentiate into plasma cells (no other ab isotypes are affected)

What is the general clinical outcome of selective IgA deficiency? (2)

Majority of cases are asymptomatic

Higher susceptibility to respiratory and genitourinary tract bacterial infections (IgA = found in mucosal membranes)

What are innate immunodeficiencies?

Defects in innate immunity

What gene is impacted by chronic granulomatous disease - phagocytosis via ROS

Phagosome oxidase (Phox) proteins

• x-linked form (70%)

• autosomal recessive form (30%)

What happens as a result of chronic granulomatous disease?

NADPH oxidative pathway used by phagocytes to generate reactive oxygen species is defective

What are three clinical outcomes of chronic granulomatous disease?

• Increase susceptibility to bacterial and fungal infections

• more inflammation as a result of insufficient pathogen clearance

• granulomas are formed to encase pathogens (lymphocytes encircle infected macrophages to wall of infection)

What gene is impacted by chediak-higashi syndrome - phagocytosis via lysosomal fusion

Lysosomal trafficking regulator gene

What happens in chediak-higashi syndrome?

Defect in microtubule function blocks lysosomal fusion with phagosome

• lysosome has hydrolytic enzymes to destroy pathogens

What is the clinical outcome of chediak-higashi syndrome? (2)

Recurrent bacterial infections from bacterial replication in phagosome

Defects in blood clotting, pigmentation, and neurologic function

What are immune regulation defects?

Defects in immune cells that play a regulatory role

What gene is impacted in autoimmune polyendocrine syndrome?

Mutation in AIRE gene seen in SP stage of T cell development

What happens in autoimmune polyendocrine syndrome?

Less self ag presentation by mTECS → escape of autoreactive T cells from the thymus

What are 3 clinical outcomes of autoimmune polyendocrine syndrome?

Organ-specific autoimmunity

Inhibition of endocrine function

Fungal infections

What gene is impacted in immune dysregulation, polyendocrinopathy, enteropathy, and X-linked (IPEX) syndrome?

Mutated and inactive FoxP3, the master gene regulatory for our Tregs

What is the clinical outcome for immune dysregulation, polyendocrinopathy, enteropathy and X-linked (IPEX) syndrome?

Severe autoimmunity

• immune destruction of bowel, pancreas, thyroid, and skin can result in death before 2 years of age

What are secondary immunodeficiencies?

Immunodeficiencies that are acquired during one’s lifetime and can be a result of several factors

What are agent-induced immunodeficiency and examples?

Environmental agents that induce immunosuppression like cytotoxic drugs and irradiation

What is acquired hypogammaglobulinemia?

Low immunoglobulin levels but normal T cell numbers; manifested by recurrent infections but no clear genetic link

Describe HIV/AIDS (secondary immunodeficiencies) cause

caused by the human immunodeficiency virus and results in the onset of AIDS as a result of CD4+ T cell depletion

What is HIV/AIDS

HIV is a retrovirus that eventually leads to the onset of AIDS

What two retroviruses are similar to HIV?

Immunodeficiency virus and feline immunodeficiency virus

What are retroviruses?

Viruses that use RNA (2 segments) as their genetic material. Upon entering host cell, they use reverse transcriptase to convert RNA → DNA which then is utilized by the host cell to create more virus

What is the 3 steps to the life cycle of HIV?

1. HIV binds to CD4+ t cells and a coreceptor (CCR5 for macrophage tropic stains or CXCR4 for T cell tropic stains) in host

   1. why humans with a 32 amino acid deletion in CCR5 → immune to receiving HIV even upon exposure

2. RNA from HIV is converted into DNA using reverse transcriptase enzyme

3. Integrase incorporates DNA into host genome

How does HIV become AIDS?

Gradual loss of immune function as a result of low CD4+ T cell count which becomes AIDS

• <200 CD4+ t cells/uL of blood

• occurrence of opportunistic infections

Defining conditions of AIDS (5)

• fungal infection of bronchi, trachea, or lungs

• cervical cancer

• kaposi’s sarcoma

• lymphoma, immunoblastic

• mycobacterium tuberculosis of any site, pulmonary, disseminated, or extrapulmonary

What is highly active antiretrovial therapy (HAART) for HIV therapies?

Daily medication & combination of drugs → chances of mutations side-stepping all drugs is unlikely. Can reduce viral loads below detectable limits but not a cure

What is pre-exposure prophylaxis (or PrEP)

Version of HAART reduces the risk of getting HIV from sex by about 99% and 74% from injection drug use

What is post-exposure prophylaxis (or PEP)

For emergency situations within 72 hours of exposure, take a pill everyday for 28 days and lowers risk of HIV infection by 80%

How is replacement of a missing protein performed? (2 bullets)

• Passive Ig injection

• Production and injection of recombinant proteins

How is replacement of a missing cell type, cell lineage, or organ performed (2 bullets)

• Bone marrow or HSC transplantation

• Thymic transplant (DiGeorge’s syndrome) → treats athymia

How is replacement of a missing or defective gene performed?

Gene therapy → CRISPR gene editing clinical trials

What is the cause of Nude mice?

Foxn1 mutation → athymia (no thymus)

What is the phenotype of Nude mice?

1. lack T cells

2. Greatly diminished B cell number (no t-cell dependent activation)

   1. B cells can still respond to t-independent antigens

What is the cause of SCID (severe combined immunodeficiency mice)

Defect in V(D)J recombination

• RAG1 and Ku70 knockout

• Prkdc knockout: missing DNA dependent protein kinase (DNA-PK) catalytic subunits that repairs ds breaks

Phenotype for SCID (severe combined immunodeficiency mice)

No B or T cells

What are hypersensitivities?

rigorous immune responses with intense and often undesirable effects; requires prior exposure

What is related to Type I hypersensitivities?

Allergic anaphylaxis and atopy

What were the 3 steps to Richet and Portier’s experiment?

1. Purified toxin from the portuguese man of war was injected into a dog

2. Dog receives localized reaction

3. Two weeks later, they inject more of the toxin into the dog

What were the expected and actual results of the Richet and Portier experiment?

• Expected: dog has less severe symptoms due to greater and faster antibody response after second infection

• Actual: dog has more severe symptoms → experienced anaphylaxis, severe allergic reaction

What is a type I hypersensitivity?

A hypersensitivity reaction that’s provoked by re-exposure to an allergen

Traits of type I hypersensitivities (3 bullets)

• dominated by IgE

• Associated with allergy and allergens, asthma, and atopy (predisposition to generating IgE against common environmental Ags)

• Common in the US, and on the rise → 30% of adults and 40% of children have at least one type I hypersensitivity

What were the steps to the Prausnitz & Kustner experiment that discovered the IgE response? (4 bullets)

Prausnitz was allergic to fish, Kustner wasn’t

1. Collect serum from Prausnitz

2. Intradermal injection of serum into Kustner’s arm

3. Wait 24 hours

4. Treat kustner’s arm with fish extract on the injection site

What were the results of the Prausnitz & Kustner experiment?

Despite not being allergic to fish initially, Kustner had an allergic reaction; something in Prausnitz’s serum contributed to immune response

What were the 4 steps in the Ishizakas first experiment (is there something in the serum?)

1. Purified serum from patients with allergies and separated fractions of this serum by size

2. Ig fractions of serum from allergic individuals were injected into volunteers

3. These volunteers were then given allergen called “E”

4. See if reaction (wheal and flare) is present

What were the results and conclusion of the Ishizakas first experiment?

Reaction was present; an Ig fraction was responsible for causing the allergic reaction → called the “E” reagin (now IgE)

What were the 4 steps of the Ishizakas second experiment (Which antibodies?)

1. Extract serum from patients with allergies to E

2. Use rabbit antibodies to remove IgG and IgA from serum

3. Treat non-allergic volunteers with IgA/IgG depleted serum fraction

4. Treat non-allergic volunteers with allergen E

What were the results and conclusion from the Ishizakas second experiment?

For both IgA and IgG, depletion of the Ig still results in an immune response; the allergic response isn’t driven by IgA or IgG

What were the 4 steps of the Ishizakas third experiment?

1. Treat mice with “E” reagin by injection

2. On right side, inject patient with just serum from allergic individuals

3. On left side, inject patient with serum from allergic individuals + serum from mice with antibodies against “e” reagin (anti-IgE antibodies)

4. Treat both sides with allergen E

What were the results and conclusion of the Ishizakas third experiment?

On side without mice serum → allergic response while no response on side with mice serum; IgE is responsible for allergic responses

What were the 3 steps for the Ishizakas 3.5 experiment?

1. Radiolabeled ragweed allergen “E” and placed it in the center of the well

2. Placed different serum fractions in areas surrounding the well

3. Observed which serum fraction the “E” allergen migrated to

What were the results and conclusion for the Ishizakas 3.5 experiment?

“E” allergen migrated to serum fraction II (containing IgE); IgE is responsible for allergic reactions

What characteristic do atopic individuals have?

predisposed to generating IgE against common environmental antigens

Characteristics of Ags (3) and how it causes allergies

• Many possess multiple epitopes or antigenic sites

• may contain motifs that mimic PAMPs

• Often possess intrinsic enzymatic activity

They irritate/disrupt epithelial cells and cleave complement

What is FCeR1

the receptor on mast cells or basophils that recognizes the Fc portion of IgE

What are the 4 steps to phase 1: sensitization of the IgE mediated allergic reaction

1. Allergen is recognized by a B cell and displayed on MHCII

2. MHCII/Allergen is recognized by T helper 2 (TH2) cell

3. TH2 cytokines (e.g. IL-4, IL-5) cause B cell to class switch to secrete IgE

4. IgE binds to mast cell or basophil via Fc receptors (FCeR1), sensitizing them

What are the 3 steps to phase 2: pathology of the IgE mediated allergic reaction

1. future exposure to Ag → high IgE secretion

2. Fc portion of IgE binds to FCeR1 on mast cell or basophil

   1. cross linking of FCeR1

3. mast cell degranulation

   1. release of histamines, cytokines, leukotrienes, prostaglandins → allergy symptoms

What is the cause of type I hypersensitivity reactions

Content inside mast cell granules: histamines, leukotrienes/prostaglandins, cytokines/chemokines

What is the formation of histamines

A molecule that’s formed from the decarboxylation of the histidine amino acid

What are the 4 effect functions of histamines

binds to one of 4 possible histamine receptors to cause:

• contraction of intestinal and bronchial smooth muscles → bronchoconstriction

• increased permeability of venules

• mucous secretion

What is the formation of leukotrienes/prostaglandins

Bioactive lipids that are formed when membrane phospholipids are enzymatically cleaved