Usmle Step 1: Immunology

Front 1

A

Back 1

Which letter points to the afferent lymphatic?

Front 2

C

Back 2

Which letter points to the efferent lymphatic?

Front 3

The capsule is a fibrous structure which surrounds the lymph node and extends inward to form trabeculae.

Back 3

What is the name of structure B and what happens there?

Front 4

Germinal center in a follicle of the cortex.

Follicle: Site of B-cell localization and proliferation. Primary follicles are dense and dormant. Secondary follicles have pale central germinal centers and are active.

Germinal center: B cells migrate here after being activated. They then change into plasma cells and migrate to the medullary cords.

Back 4

What is the name of structure D and what happens there?

Front 5

Medullary cord, which contains closely packed T-cells and plasma cells (which came from the germinal centers). The cords are separated from each other by medullary sinuses.

Back 5

What is the name of structure E and what happens there?

Front 6

Medullary sinus. These separate the medullary cords and communicate with efferent lymphatics. They contain reticular cells and macrophages.

Back 6

What is the name of structure F and what happens there?

Front 7

Trabecula. Extension of the fibrous capsule

Back 7

What is the name of structure G and what happens there?

Front 8

Connective tissue (C is capsule)

Back 8

Lymph node: What is A?

Front 9

Afferent lymphatic vessel with valve

Back 9

Lymph node: What is B?

Front 10

Capsule

Back 10

Lymph node: What is C?

Front 11

Subcapsular (marginal) sinus

Back 11

Lymph node: What is D?

Front 12

Trabecula

Back 12

Lymph node: What is E?

Front 13

Trabecular (cortical) sinuses

Back 13

Lymph node: What is F?

Front 14

Germinal center of lymphatic nodule/follicle

Back 14

Lymph node: What is G?

Front 15

Paracortex (deep cortex): Houses T cells. Contains high endothelial venules through which T and B cells enter from blood.

Greatly enlarged in extreme cellular immune response (ie viral).

Not well developed in DiGeorge syndrome

Back 15

Lymph node: What is H?

Front 16

Medullary cords

Back 16

Lymph node: What is I?

Front 17

Medullary sinuses

Back 17

Lymph node: What is J?

Front 18

Venule and arteriole

Back 18

Lymph node: What is K?

Front 19

Subcapsular marginal sinus

Back 19

Lymph node: What is L?

Front 20

Lymphatic nodule/follicle

Back 20

Lymph node: What is M?

Front 21

Trabecula

Back 21

Lymph node: What is N?

Front 22

Germinal center of lymphatic nodule/follicle

Back 22

Lymph node: What is O?

Front 23

Trabecular blood vessels

Back 23

Lymph node: What is P?

Front 24

Paracortex (deep cortex): Houses T cells. Contains high endothelial venules through which T and B cells enter from blood.

Greatly enlarged in extreme cellular immune response (ie viral).

Not well developed in DiGeorge syndrome

Back 24

Lymph node: What is Q?

Front 25

Medullary sinuses

Back 25

Lymph node: What is R?

Front 26

Medullary cords

Back 26

Lymph node: What is S?

Front 27

Lymph drainage: What does the right lymphatic duct drain?

Back 27

Right arm and right half of head

Front 28

Lymph drainage: What does the thoracic duct drain?

Back 28

Everything except for the right arm and the right half of head

Front 29

Splenic sinusoids: What are they?

Back 29

Long, vascular channels in red pulp with fenestrated "barrel hoop" basement membrane and macrophages nearby. Adjacent to splenic cords and contain blood.

Front 30

How can the spleen be distinguished from a lymph node on histologic section?

Back 30

Spleens have no subscapsular sinus and no cortex or medulla. They have white pulp and red pulp.

Front 31

What does the white pulp of the spleen contain?

Back 31

Contains:
1. Lymphoid follicles with germinal centers (mostly B cells). Can see aggregation of dark basophilic lymphocytic nuclei.
2. Characteristic central arterioles. Surrounded by a Periarterial lymphatic sheath (PALS) which is a collection of T-lymphocytes.

Front 32

Where is the red pulp of the spleen located?

Back 32

Around and between the lymphatic nodules of the white pulp

Front 33

Splenic cords: What are they?

Back 33

Structures containing macrophages, plasma cells, lymphocytes, and few RBCs. Separated from each other by splenic sinusoids.

Front 34

Thymus: Function

Back 34

Site of T-cell differentiation and maturation (T cells differentiate in the Thymus. B cells differentiate in the Bone marrow)

Front 35

Thymus: Embryological origin

Back 35

Epithelium of 3rd branchial pouches

Front 36

Lymphocytes: Embryological origin

Back 36

Mesenchyme

Front 37

Thymus: What does the cortex contain and what does it look like?

Back 37

The lobules resemble lymphatic nodules except they are angular, not round.

Contains:
1. Densely packed (dark) immature T cells.
2. Large epithelial reticular cells which appear as holes within the cortical cells.

Front 38

Thymus: What does the medulla contain and what does it look like?

Back 38

Pale

Contains:
Thymic (Hassall's) corpuscles which have a lamellated or whorled appearance due to degenerating epithelial reticular cells.

Front 39

What percentage of T cells which enter thymus survive?

Back 39

2%

Front 40

What is positive selection of T cells?

Back 40

Retention of T cells that have functioning T cell receptors

Front 41

Where do positive and negative selection of T-cells occur in the thymus?

Back 41

At the corticomedullary junction

Front 42

What is negative selection of T cells?

Back 42

Destruction of T-cells that react to self-antigen

Front 43

Innate immunity vs adaptive immunity: How are receptors that recognize pathogens encoded?

Back 43

Innate: Germline encoded
Adaptive: Undergo VDJ recombination during development

Front 44

Innate immunity vs adaptive immunity: How fast is response to pathogens?

Back 44

Innate: Always fast, no memory response.
Adaptive: Slow on 1st exposure but memory response is faster and more robust.

Front 45

Innate immunity or adaptive immunity: Neutrophils

Back 45

Innate immunity

Front 46

Innate immunity or adaptive immunity: Macrophages

Back 46

Innate immunity

Front 47

Innate immunity or adaptive immunity: Dendritic cells

Back 47

Innate immunity

Front 48

Innate immunity or adaptive immunity: Complement

Back 48

Innate immunity

Front 49

Innate immunity or adaptive immunity: T cells

Back 49

Adaptive immunity

Front 50

Innate immunity or adaptive immunity: B cells

Back 50

Adaptive immunity

Front 51

Innate immunity or adaptive immunity: Circulating antibody

Back 51

Adaptive immunity

Front 52

T-cell differentiation: Where do T-cell precursors come from and where do they go?

Back 52

From the bone marrow to the thymus

Front 53

T-cell differentiation: What CD?

Back 53

CD3

Front 54

T-cell differentiation: What happens to T-cell precursors when they enter the thymus, and what are they called?

Back 54

Once T-cell precursors acquire and display CD4 and CD8, they are cortical thymocytes.

Front 55

T-cell differentiation: Where is the T-cell in its development when it undergoes positive selection?

Back 55

Both CD4 positive and CD8 positive

Front 56

T-cell differentiation: Where in the thymus are cells which are positive for both CD4 and CD8 located?

Back 56

Thymic cortex

Front 57

T-cell differentiation: Where is the T-cell in its development when it undergoes negative selection?

Back 57

Either CD4 positive or CD8 positive, not both

Front 58

T-cell differentiation: Where in the thymus are cells which are positive for either CD4 or CD8 located?

Back 58

Thymic medulla

Front 59

T-cell differentiation: What are the two types of helper T cells and where do they differentiate?

Back 59

In the lymph node, helper T cells differentiate into Th1 cells, and Th2 cells.

Front 60

Differences between Th1 and Th2 cells: Stimulant for differentiation from archetypical helper T cell.

Back 60

Th1: IL-12 from both other Th1 cells and antigen-presenting dendritic cells

Th2: IL-4 from other Th2 cells and presumably an unknown factor from dendritic cells

Front 61

Differences between Th1 and Th2 cells: Cytokines produced by both types

Back 61

Both: IL-2
Th1: IFN-gamma, TNF-alpha
Th2: IL-4, IL-5, IL-6, IL-10, IL-13

Front 62

Cytokine effects: Interleukin 2

Back 62

Stimulates T-cell growth and proliferation

Mnemonic for first 5 interleukins: Hot T-bone stEAk

Front 63

Cytokine effects: Interferon gamma

Back 63

1. Inhibits Th2 cytokines
2. Induces class I and II MHC
3. Stimulates differentiation of monocytes into macrophages.
4. Activates macrophages.

Front 64

Cytokine effects: Tumor Necrosis Factor alpha

Back 64

1. Activates macrophages, neutrophils (also attracts them), and CD8 cells.
2. Induces neutrophil-endothelial cell adhesion.
3. Constitutional: sepsis, cachexia ("wasting away"), fever, acute phase proteins.
4. Tumor cell lysis
5. Increased proliferation of B-cells
6. Increased synthesis of IL-2 receptors by Th cells.
7. Stimulates dendritic cell migration to lymph nodes.

Front 65

Cytokine effects: Interleukin 4

Back 65

1. Growth of B-cells
2. Growth and proliferation of T-cells
3. Synthesis of IgE
4. Class switching of IgG to IgE
5. Inhibits IL-8, IL-1, and TNF-alpha

Mnemonic for first 5 interleukins: Hot T-bone stEAk. E as in stimulates IgE production.

Front 66

Cytokine effects: Interleukin 5

Back 66

1. Differentiation of B cells 2. Class switching of IgA
3. Production and activation of eosinophils

Mnemonic for first 5 interleukins: Hot T-bone stEAk. A as in stimulates IgA production.

Front 67

What cytokines stimulate the acute phase response?

Back 67

1. IL-1
2. IL-6
3. TNF-alpha

Front 68

What are acute phase response proteins used for?

Back 68

1. Augment immune response (complement, Ig)
2. Regulate the extent of response (protease inhibitors like alpha-1-antitrypsin)
3. Stimulate additional responses (alpha-2-macroglobulin)

Front 69

Cytokine effects: Interleukin 10

Back 69

Big picture: Stimulates Th2 while inhibiting Th1

Specifically inhibits:
1. IL-8
2. IL-1
3. TNF-alpha
4. IFN-gamma

Front 70

What releases: Interleukin 10

Back 70

1. Th2 cells
2. Macrophages

Front 71

Differences between Th1 and Th2 cells: Major effects

Back 71

Both: Downregulate each other

Th1: Activates all lymphocytes and APCs, especially CD8 cells and macrophages.

Th2 cells:
1. B cells: Increased differentiation, proliferation, antibody, and class switching.
2: Activation of eosinophils

Front 72

What releases: Interleukin 2

Back 72

Th cells

Front 73

What releases: Tumor Necrosis Factor alpha

Back 73

Macrophages (emphasized) and Th1 cells

Front 74

What releases: Interferon gamma

Back 74

Th1 cells (emphasized) and NK cells

Front 75

What releases: Interleukin 5

Back 75

T cells (especially Th2) and mast cells

Front 76

What releases: Interleukin 6

Back 76

T cells (especially Th), macrophages, and endothelial cells

Front 77

What is MHC and what codes for it?

Back 77

Major Histocompatability Complex encoded by Human Leukocyte Antigen (HLA)

Front 78

What genes code for MHC I?

Back 78

1. HLA-A
2. HLA-B
3. HLA-C

Front 79

What genes code for MHC II?

Back 79

1. HLA-DP
2. HLA-DQ
3. HLA-DR

Front 80

MHC I and II: What cells are they expressed on?

Back 80

I: All nucleated cells except sperm.
II: Antigen Presenting Cells

Front 81

MHC I and II: Where in the cell is antigen loaded onto the MHC?

Back 81

I: RER (mostly intracellular peptides)
II: Acidified endosome

Front 82

B cells and T cells: Effect on Ig

Back 82

B cells: Make it

T cells: (CD4) Help B cells make it and release IFN-gamma to activate macrophages

Front 83

B cells and T cells: Method of killing

Back 83

B cells: IgG opsonizes bacteria and viruses

T cells: (CD8) Directly kills virus-infected cells

Front 84

B cells and T cells: Allergy mechanism

Back 84

B: Type I hypersensitivity, through IgE

T: Type IV hypersensitivity

Front 85

B cells and T cells: Organ rejection speed

Back 85

B: Fast, through antibodies

T: Slow

Front 86

CD/MHC: What binds MHC II?

Back 86

CD4 T-cell receptors

Front 87

What does MHC I pair with (allosteric interaction)

Back 87

beta2-microglobulin

Front 88

CD/MHC: What binds MHC I?

Back 88

CD8 T-cell receptors

Front 89

CD/MHC: What binds CD4 T-cell receptors?

Back 89

MHC II on antigen presenting cells

Front 90

CD/MHC: What binds CD8 T-cell receptors?

Back 90

MHC I on virus-infected cells

Front 91

Cytokine effects: Interleukin 1

Back 91

Big picture: Stimulates growth differentiation or product synthesis by T cells, B cells, neutrophils, fibroblasts, and epithelial cells

1. Endogenous pyrogen
2. Activates T cells
3. Upregulates adhesion molecules
4. Induces acute phase reactants
5. Synergizes with TNF-alpha

Mnemonic for first 5 interleukins: Hot T-bone stEAk. Hot as in fever.

Front 92

What releases: Interleukin 1

Back 92

1. Professional antigen-presenting cells (macrophages, monocytes, dendritic cells, and B cells)
2. Some non-professional antigen presenting cells (fibroblasts, endothelial cells, others)

Front 93

How does Interleukin 1 cause fever?

Back 93

Steps
1. Migrates to the circumventricular organs
2. Binds with endothelial receptors.
3. Receptors activate Phospholipase A2-COX2-PGE2 pathway
4. Prostaglandin E2's presence in the hypothalamus elevates the thermoregulatory set point and activates neuroendocrine determinants of fever.

Front 94

What are the professional antigen presenting cells?

Back 94

1. Macrophages
2. B cells
3. Dendritic cells

Front 95

What is the CD3 complex?

Back 95

Cluster of polypeptides associated with a T-cell receptor. It is important in signal transduction.

Front 96

How are Th cells activated?

Back 96

1. APC phagocytoses foreign body.
2. APC presents antigen on MHC II.
3. Signal 1: Th cell's TCR recognizes antigen.
4. Signal 2 (costimulatory): APC's B7 molecule stimulates Th cell's CD28 molecule.
5. Autocrine IL-2 stimulates Th cell to produces cytokines

Front 97

How are Tc cells activated?

Back 97

1. Virus-infected cell presents endogenously synthesized proteins on MHC I.
2. Signal 1: Tc cell's TCR recognizes antigen.
3. Signal 2: IL-2 released from Th cell activates T c cell to kill virus infected cell.

Front 98

Antibody structure/function: What are the components of the heavy chain?

Back 98

Variable: VH
Constant: CH1, CH2, CH3

Front 99

Antibody structure/function: What are the components of the light chain?

Back 99

Variable: VL
Constant: CL

Front 100

What part of an antibody recognizes antigen?

Back 100

Variable portion of Fab fragment

Front 101

What part of an antibody fixes complement?

Back 101

Constant part of H chain of IgM and IgG

Front 102

Antibody structure/function, True or False: Light chain contributes to Fab

Back 102

True

Front 103

Antibody structure/function, True or False: Heavy chain contributes to Fab

Back 103

True

Front 104

Antibody structure/function, True or False: Light chain contributes to Fc

Back 104

False

Front 105

Antibody structure/function, True or False: Heavy chain contributes to Fc

Back 105

True

Front 106

What is the middle of the variable component of an antibody component chain called?

Back 106

Hypervariable region

Front 107

Antibody structure/function: Where on an antibody is the hypervariable region?

Back 107

The majority of the variable segments excluding the edges

Front 108

How are the four chains of an antibody connected?

Back 108

Interchain disulfide bonds at:
1. between the two heavy chains on the Fc side of the hinge region
2. between corresponding light and heavy chains on the Fab side of the hinge region

Front 109

What disulfide bonds does an antibody have?

Back 109

Interchain: Bonds between both heavy chains and between corresponding light and heavy chains

Intrachain: On each segment

Front 110

Where on an antibody is the Amino terminal?

Back 110

At the variable edges of the chains

Front 111

Where on an antibody is the carboxyl terminal?

Back 111

At the constant edges of the heavy chains

Front 112

Antibody structure/function: What are the five Cs of Fc?

Back 112

1. Constant
2. Carboxy terminal
3. Complement binding (IgG and IgM only)
4. Carbohydrate side chains
5. Complement binding fragment

Front 113

3 main functions of the antibody

Back 113

1. Opsonization
2. Neutralization (prevents bacterial adherence)
3. Complement activation

Front 114

How is antibody diversity generated?

Back 114

1. Random "recombination" of VJ (light chain) or VDJ (heavy chain) genes.
2. Random combination of heavy chains with light chains
3. Somatic hypermutation
4. Addition of nucleotides to DNA during "genetic recombination" by terminal deoxynucleotidyl transferase.

Front 115

What does terminal deoxynucleotidyl transferase do?

Back 115

Addition of nucleotides to DNA during "genetic recombination" in B cells

Front 116

What does Tdt stand for?

Back 116

Terminal deoxynucleotidyl transferase

Front 117

Which immunoglobulins are expressed on the surface of mature B cells?

Back 117

IgM and IgD

Front 118

What is isotype switching?

Back 118

Differentiation of B cells into plasma cells that secrete IgG, IgA, or IgE

Front 119

What stimulates isotype switching?

Back 119

Cytokines (IL-4 and IL-5) and CD40-Ligand on T-cells

Front 120

Main antibody isotype in secondary immune response

Back 120

IgG

Front 121

Most abundant antibody isotype

Back 121

IgG

Front 122

Antibody isotypes which cross placenta

Back 122

IgG

Front 123

Antibody isotypes which fix complement

Back 123

IgG and IgM in the classic complement pathway

Mnemonic: GM makes classic cars

Front 124

Antibody isotypes which opsonize bacteria

Back 124

IgG (and IgA weakly)

Front 125

Main antibody isotype in primary immune response

Back 125

IgM

Front 126

Antibody isotypes associated with the J chain

Back 126

IgM and IgA

Front 127

Antibody isotypes associated with the SP

Back 127

IgA

SP = Secretory Protein

Front 128

Antibody isotype with longest half life

Back 128

IgG (26 days compared with 5 for IgM, the next longest)

Front 129

Antibody isotype which prevents bacterial/viral attachment to mucous membranes

Back 129

IgA

Front 130

Antibody isotype found in secretions

Back 130

IgA

Front 131

Antibody isotype which mediates type I hypersensitivity

Back 131

IgE

Front 132

How does IgE cause an allergic response?

Back 132

Type I hypersensitivity
1. IgE binds to basophils or mast cells
2. IgE binds antigen
3. These cells release histamine and leukotrienes.

Front 133

Which cells have receptors for IgE?

Back 133

1. mast cells
2. basophils
3. eosinophils
4. monocytes/macrophages
5. platelets

Front 134

Antibody isotype which mediates immunity to worms

Back 134

IgE

Front 135

Least abundant antibody isotype

Back 135

IgE

Front 136

Define allotype

Back 136

An individual's allele coding for the constant portions of the antibody's heavy chains.

Front 137

Define isotype

Back 137

Type of chain in an antibody

Heavy isotypes: alpha, gamma, delta, epsilon, mu

Light isotypes: kappa, lambda

Front 138

Define idiotype

Back 138

antibodies of one idiotype share structure of their variable region and thus, antigen binding specificity.

Front 139

Cytokine effects: Interleukin 3

Back 139

Supports the growth and differentiation of bone marrow stem cells (similar to GM-CSF). Most important during early growth.

Mnemonic for first 5 interleukins: Hot T-bone stEAk. bone, as in bone development

Front 140

What releases: Interleukin 3

Back 140

T cells (emphasis on activated T cells) and thymic epithelial cells

Front 141

Cytokine effects: Interleukin 6

Back 141

1. Differentiation and growth of B cells and T cells
2. Systemic effects (Acute Phase Response and Fever)
3. Stimulates Ig production

Front 142

What releases: Interleukin 4

Back 142

Th2 cells

Front 143

Cytokine effects: Interleukin 8

Back 143

1. Major neutrophil chemotactic and adhesion factor
2. Angiogenesis
3. High levels associated with schizophrenia

Front 144

What releases: Interleukin 8

Back 144

1. Monocytes
2. Endothelial cells
3. Fibroblasts

Front 145

Cytokine effects: Interleukin 12

Back 145

1. Promotes differentiation of Th cells into Th1
2. Activates NK cells

Front 146

What releases: Interleukin 12

Back 146

Professional Antigen Presenting Cells:
1. Dendritic cells
2. Macrophages
3. B cells

Front 147

Important cell surface proteins and their functions: Helper T cells

Back 147

1. CD4
2. TCR
3. CD3 (Signal transduction)
4. CD28 and CD40L (Receive costimulatory activation signal respectively from B7 and CD40 which are both on B cells and professional APCs. These two signaling pathways each upregulate the other.)

Front 148

Important cell surface proteins and their functions: Cytotoxic T cells

Back 148

1. CD8
2. TCR
3. CD3 (Signal transduction)

Front 149

Important cell surface proteins and their functions: B cells

Back 149

1. IgM
2. MHC II (Presents foreign antigens to Th cells)
2. B7 and CD40 (Costimulatory activation signal respectively to CD28 and CD40L which are both on T cells. These two signaling pathways each upregulate the other.)
2. CD19, CD21 (Subunits of co-receptor for BCR complex)
4. CD20 (Target in non-Hodgkin's lymphoma of monoclonal antibodies like rituximab)

Front 150

Important cell surface proteins and their functions: Macrophages

Back 150

1. MHC II (Presents foreign antigens to Th cells)
2. CD14 (Works with toll-like receptor 4 to bind lipopolysaccharide. Also a marker for monocytes)
3. Receptors for Fc and C3b (ie opsonins)

Front 151

Important cell surface proteins and their functions: NK cells

Back 151

1. Receptors for MHC I
2. CD16 (subunit of low-affinity Fc receptor [ie. opsonins])
3. CD56 (adhesion molecule)

Front 152

Important cell surface proteins and their functions: Hematopoietic stem cells

Back 152

CD34 (marker for this type of cell, and a receptor for CD62L, a selectin)

Front 153

Complement: Viral neutralization

Back 153

C1, C2, C3, C4

Front 154

Complement: Opsonization

Back 154

C3b

Front 155

Complement: Anaphylatoxins

Back 155

C3a, C5a

Front 156

Complement: Neutrophil Chemotaxis

Back 156

C5a

Front 157

Complement: Membrane attack complex

Back 157

C5b to C9

Front 158

Deficiency of C1 esterase inhibitor leads to:

Back 158

Hereditary angioedema (overactive complement)

Front 159

Deficiency of C3 leads to:

Back 159

Severe recurrent pyogenic sinus and respiratory tract infections

Front 160

Deficiency of C6 through C8 leads to:

Back 160

Neisseria bacteremia

Front 161

What is Decay Accelerating Factor?

Back 161

Prevents attachment of the alternative complement complex (C3 convertase) to the membrane

Front 162

When is Decay Accelerating Factor missing?

Back 162

In paroxysmal nocturnal hemoglobinuria

Front 163

What kind of bacteria does complement defend against?

Back 163

Gram negative bacteria

Front 164

What activates the classic complement pathway?

Back 164

IgG and IgM.

Mnemonic: GM makes classic cars.

Front 165

What activates the alternative complement pathway?

Back 165

Microbe surface molecules (especially endotoxin)

Front 166

PGI2

Back 166

Prostacyclin. Vasodilator and inhibits platelet aggregation. Aspirin does not inhibit its synthesis by endothelial cells. Synthesized from PGH2 by prostacyclin synthase in intact endothelial cells.

Front 167

PGH2

Back 167

Synthesizes PGI2 with prostacyclin synthase in intact endothelial cells. Precursor of thromboxanes. Synthesized from PGG2.

Front 168

PGE2

Back 168

Vasodilation, pain and fever. Synthesized from PGH2

Front 169

TxA2

Back 169

Vasoconstriction, platelet aggregation and bronchoconstriction. Coverted from PGH2 by thromboxane synthase.

Front 170

LTB4

Back 170

chemotaxis and activation of neutrophil adhesion molecules

Front 171

LTC4

Back 171

Vasoconstriction, increased vessel permeability, bronchoconstriction

Front 172

LTD4

Back 172

Vasoconstriction, increased vessel permeability, bronchoconstriction

Front 173

LTE4

Back 173

Vasoconstriction, increased vessel permeability, bronchoconstriction