Immunology

What is the function of the inhibitory arm of an NK Cell?

It recognizes MHC I on self cells, preventing the NK cell from killing them.

What is the function of the activating arm of an NK Cell?

It is NKG2D, which binds to ligands on virus-infected and cancer cells, triggering cell killing.

Which interleukins are associated with the function of NK cells?

IL-2, IL-12, and IL-15.

What are the key surface markers for Natural Killer (NK) cells?

CD16, CD56, and CD94.

What is the universal marker for all T cells?

CD3, which is part of the T-cell receptor signal transduction molecule.

What is the surface marker for Helper T cells?

CD4.

What is the surface marker for Cytotoxic T cells?

CD8.

What is the normal ratio of CD4+ to CD8+ T cells in the blood?

2:01

How does the CD4:CD8 ratio change in a patient with HIV?

The ratio reduces.

In which condition does the CD4:CD8 ratio characteristically increase?

Sarcoidosis.

Approximately 95% of T-cell receptors (TCR) are of the _ type.

$\alpha\beta$ TCR.

The remaining 5% of T-cell receptors (TCR) are of the $\gamma\delta$ type and are primarily found in which locations?

The gastrointestinal tract (GIT) and genitourinary tract (GUT).

What is the primary interleukin associated with Th1 cells?

IL-2.

What is the function of IL-2 released by Th1 cells?

It stimulates other Th1 cells (autocrine stimulation).

What is the function of IL-2 released by Th2 cells?

It stimulates Th1 cells (paracrine stimulation).

What is the function of IFN-$\gamma$ released by Th1 cells?

It stimulates macrophages, leading to granuloma formation.

Which interleukin, produced by Th2 cells, is responsible for isotype switching in B cells?

IL-4.

Which interleukin, secreted by Th2 cells, is responsible for eosinophil activation?

IL-5.

Which interleukin, produced by Th2 cells, promotes mucus production?

IL-13.

What is the signature cytokine produced by Th17 cells?

IL-17.

CD8+ T cells are also known as _ T cells.

Cytotoxic

What is the apoptosis-inducing pathway used by cytotoxic T cells that involves a receptor-ligand interaction?

The CD95 (Fas) pathway.

What is the main enzymatic pathway used by cytotoxic T cells to induce cell killing?

The Perforin Granzyme pathway.

What is the most common pan B cell marker?

CD19.

Besides CD19, what are some other surface markers found on B cells?

CD10, CD20, CD21, CD22, CD23, CD40, CD79a, and CD79b.

What molecule is responsible for signal transduction in B cells?

CD79a and b.

Which B cell surface marker serves as the entry point for the Epstein-Barr virus (EBV)?

CD21.

What interaction between B cells and T cells is essential for T cell-dependent B cell activation?

The interaction between CD40 on B cells and CD40 ligand (CD40L) on T cells.

The interaction between CD40 and CD40L leads to the T cell releasing which cytokine to promote isotype switching?

IL-4.

What is the primary role of Antigen-presenting cells (APCs)?

They are the first cells to pick up an antigen and present it to T cells.

What are the three types of professional antigen-presenting cells (APCs)?

Dendritic cells, B cells, and Macrophages.

List three examples of nonprofessional antigen-presenting cells (APCs).

Thymic epithelial cells, Endothelial cells, and Fibroblasts.

The Major Histocompatibility Complex (MHC) is encoded by the HLA gene, located on the short arm of which chromosome?

Chromosome 6p.

Which specific HLA genes encode for MHC class I proteins?

HLA-A, HLA-B, and HLA-C.

Which specific HLA genes encode for MHC class II proteins?

HLA-DP, HLA-DQ, and HLA-DR.

What is encoded by the HLA part III region, located between the MHC class I and II genes?

Complement proteins (C2, C4), Heat shock proteins (HSP), and TNF $\alpha$.

Describe the polypeptide chain structure of an MHC class I molecule.

It consists of one heavy chain with three domains ($\alpha1$, $\alpha2$, $\alpha_3$) and one light chain (β2-microglobulin).

Describe the polypeptide chain structure of an MHC class II molecule.

It consists of two chains, an alpha chain ($\alpha1$, $\alpha2$) and a beta chain ($\beta_1$, β2).

The antigen binding cleft of an MHC class I molecule is formed by which domains?

The $\alpha1$-$\alpha2$ junction.

The antigen binding cleft of an MHC class II molecule is formed by which domains?

The $\alpha1$-$\beta1$ junction.

On which cells are MHC class I molecules present?

On all nucleated cells and platelets.

Which two cell types specifically lack MHC class I molecules?

Red blood cells and sperm cells.

On which cells are MHC class II molecules present?

Only on antigen-presenting cells (APCs).

MHC class I molecules present antigens to which type of T cells?

CD8+ T cells (cytotoxic T cells).

MHC class II molecules present antigens to which type of T cells?

CD4+ T cells (helper T cells).

What is the mnemonic for the four types of hypersensitivity reactions?

ACID (Anaphylaxis, Cytotoxicity, Immune complex, Delayed type).

What is the mnemonic for remembering examples of Type I hypersensitivity?

ABCD (Allergies, Bronchial asthma, Chromosomes/genetic determinant, Drugs).

Type I hypersensitivity includes allergic conditions such as allergic _, rhinitis, and allergic conjunctivitis.

dermatitis

Which diagnostic skin test is an example of a Type I hypersensitivity reaction?

Positive PK reaction (Prausnitz–Küstner reaction).

The Theobald-Smith phenomenon is an example of which type of hypersensitivity reaction?

Type I hypersensitivity.

What is the underlying mechanism of Type II hypersensitivity?

Cytotoxicity mediated by antibodies against cell surface antigens.

Goodpasture's syndrome and Rh incompatibility are examples of which type of hypersensitivity?

Type II hypersensitivity.

Pemphigus (bullous) and pernicious anemia are examples of which type of hypersensitivity?

Type II hypersensitivity.

Type V hypersensitivity is a subtype of Type II where antibodies are directed against what?

Cellular receptors.

In Myasthenia gravis, antibodies are directed against which receptors, causing a Type V hypersensitivity reaction?

Acetylcholine receptors.

In Grave's disease, antibodies are directed against which receptors, causing a Type V hypersensitivity reaction?

TSH receptors.

What is the underlying mechanism of Type III hypersensitivity?

Tissue damage caused by the deposition of antigen-antibody immune complexes.

Systemic lupus erythematosus (SLE) and serum sickness are classic examples of which type of hypersensitivity?

Type III hypersensitivity.

The Arthus reaction, a localized immune complex disease, is an example of which hypersensitivity type?

Type III hypersensitivity.

Post-streptococcal glomerulonephritis (PSGN), presenting with cola-colored urine, is an example of _ hypersensitivity.

Type III

What is the underlying mechanism of Type IV hypersensitivity?

It is a delayed-type, T-cell mediated reaction.

The formation of granulomas, as seen in tuberculosis, is a hallmark of which hypersensitivity type?

Type IV hypersensitivity.

The Mantoux test for TB and the Lepromin test are examples of skin tests that elicit which type of hypersensitivity reaction?

Type IV hypersensitivity.

Multiple sclerosis and inflammatory bowel disease are examples of which type of hypersensitivity?

Type IV hypersensitivity.

Contact dermatitis, such as that caused by poison ivy or artificial jewelry (Ni, Cd), is what type of hypersensitivity reaction?

Type IV hypersensitivity.

Rheumatoid arthritis involves which two types of hypersensitivity reactions?

Type III and Type IV hypersensitivity.

Hypersensitivity pneumonitis involves which two types of hypersensitivity reactions?

Type III and Type IV hypersensitivity.

Systemic Lupus Erythematosus (SLE) involves which two types of hypersensitivity reactions?

Type II and Type III hypersensitivity.

Hyperacute transplant rejection is what type of hypersensitivity reaction?

Type II.

Acute transplant rejection can involve which two types of hypersensitivity reactions?

Type II and Type IV.

Chronic transplant rejection is what type of hypersensitivity reaction?

Type IV.

What is the most sensitive antibody test for Systemic Lupus Erythematosus (SLE)?

ANA (antinuclear antibody).

What is the most specific antibody test for Systemic Lupus Erythematosus (SLE)?

ASA (anti-Smith antibody).

Which antibody test is considered both sensitive and specific for Systemic Lupus Erythematosus (SLE)?

Anti-dsDNA antibody.

Which antibody is associated with neonatal lupus?

Anti-Ro antibody.

Which antibody is associated with SLE with psychosis?

Anti-ribosomal P antibody.

Which antibody is characteristic of drug-induced lupus?

Anti-histone antibody.

What is the mnemonic for drugs that can cause drug-induced lupus?

SHIP D (Sulfonamides, Hydralazine, Isoniazid, Procainamide, Dapsone).

What is the most sensitive antibody for Sjogren Syndrome?

Anti-SS-A (Anti-Ro).

What is the most specific antibody for Sjogren Syndrome?

Anti-SS-B (Anti-La).

The presence of anti-centromeric antibody is associated with which form of scleroderma?

Limited scleroderma.

The presence of anti-topoisomerase antibody (Anti-Scl 70) is associated with which form of scleroderma?

Diffuse scleroderma.

A homogenous pattern on immunofluorescence is associated with antibodies against what?

Anti-chromatin, histone, and nuclear antibodies.

A peripheral or rim pattern on immunofluorescence is associated with which antibody?

Anti-dsDNA antibody.

A nuclear pattern on immunofluorescence is associated with antibodies against what?

Antibodies against RNA.

A speckled immunofluorescence pattern, the most common pattern, is associated with which antibodies?

Anti-Smith (SLE) and anti-Ro/La (Sjogren's syndrome).

A centromeric pattern on immunofluorescence is associated with which antibody?

Anti-centromeric antibody (limited scleroderma).

What is the most common defect causing X-linked severe combined immunodeficiency (SCID)?

A defect in the $\gamma$ subunit of cytokine receptors.

What are the common genetic defects in autosomal recessive SCID?

ADA deficiency, JAK-3 gene defect, or RAG-1/2 gene defects.

What is a characteristic clinical feature in a child with SCID?

Morbilliform rash.

What is the underlying genetic defect in Bruton's hypogammaglobulinemia?

A defect in the BTK gene (Bruton's tyrosine kinase).

Bruton's hypogammaglobulinemia primarily affects boys and leads to decreased IgG levels and defective _.

opsonin

What is the underlying genetic cause of Bare lymphocyte syndrome?

A deficiency or absence of MHC class II molecules.

What is the genetic basis of DiGeorge syndrome?

Deletion of chromosome 22q.

What are the key developmental defects in DiGeorge syndrome?

Thymus not formed (T-cell defect), Parathyroid not formed (hypocalcemia), Cleft lip/palate, Abnormal facies, and Tetralogy of Fallot.

What is the genetic defect in Hyper IgM syndrome?

A defect in the CD40 receptor or CD40 ligand.

Patients with Hyper IgM syndrome are particularly susceptible to which opportunistic infection?

Pneumocystis jirovecii pneumonia.

What is the genetic defect in Hyper IgE syndrome (Job syndrome)?

A defect in the STAT3 gene.

What does the mnemonic FATE stand for in Hyper IgE syndrome?

F-Coarse facies, A-Cold abscess (Staphylococcus), T-Primary teeth retention, E-IgE elevated and Eczema.

What is the underlying defect in isolated IgA deficiency?

IgA deficiency.