Anatomy of Immune response

Question 1

What are the first barriers to infection at body surfaces?

Answer 1

The skin and mucosae act as primary barriers to pathogens.

Question 2

What is the function of keratinocytes in skin immunity?

Answer 2

Provide a physical barrier.
Express pattern recognition receptors (PRRs) like TLRs, NOD-like receptors, RIG-1-like receptors, and C-type lectins.
Produce microbicidal compounds (e.g., β-defensins).
Release cytokines and chemokines to recruit immune cells.

Question 3

What immune cells are found in the epidermis?

Answer 3

Langerhans cells (antigen-presenting cells).
T-cells (both αβ and γδ T-cells).

Question 4

What immune cells are present in the dermis?

Answer 4

Dendritic cells, macrophages, T-cells (αβ and γδ), NK cells, and mast cells.

Question 5

How do T-cells home to the skin?

Answer 5

They upregulate adhesion molecules like CLA, CD43, CD44.
These molecules bind to E-selectin on blood vessel endothelium.
Other interactions include LFA-1 & Mac-1 (binding ICAM-1) and VLA-4 (binding VCAM-1).

Question 6

What happens during an inflammatory response in the skin?

Answer 6

Leukocyte migration increases.
Neutrophils, monocytes, and eosinophils are recruited.
In atopic eczema, the number of leukocytes in the skin increases substantially.

Question 7

What is the function of Peyer’s patches?

Answer 7

They are the inductive sites for gut immune responses.
M-cells transport antigens to APCs, which activate lymphocytes.

Question 8

What is the role of CD103+ dendritic cells in the gut?

Answer 8

Convert vitamin A to retinoic acid.
Retinoic acid imprints gut-homing signals on T-cells and B-cells.

Question 9

What receptors help T-cells home to the gut?

Answer 9

LPAM-1 (α4β7 integrin) binds to MAdCAM-1 in the lamina propria.
CCR9 (chemokine receptor) directs T-cells to the gut.

Question 10

What types of immune cells are found in the lamina propria?

Answer 10

Memory/activated T-cells, regulatory T-cells (Foxp3+ Tregs), and IgA-producing B-cells.

Question 11

How does IgA function in gut immunity?

Answer 11

IgA binds pathogens in the lumen to prevent them from entering cells.
Transported via the poly-Ig receptor to the gut lumen.

Question 12

What are intraepithelial lymphocytes (IELs), and how do they function?

Answer 12

Specialized T-cells in the intestinal epithelium.
Express αEβ7 integrin, which binds E-cadherin on epithelial cells.
Many IELs are CD8+ T-cells that provide rapid immune responses.

Question 13

What is the difference between αβ and γδ T-cells in the gut?

Answer 13

αβ T-cells → Conventional TCRs, recognize peptide–MHC complexes.
γδ T-cells → Respond rapidly to stress signals, important for first-line defense.

Question 14

What is the role of IL-10 and TGF-β in gut immunity?

Answer 14

Suppress excessive immune responses.
Prevent damage to the gut from overactive inflammation.

Question 15

How do T-cells home to other mucosal sites (lungs, etc.)?

Answer 15

Chemokines CXCL10 and CCL5 attract CXCR3+ and CCR5+ T-cells to the lungs.
Specific homing receptors interact with high endothelial venules (HEVs).

Question 17

What are pattern recognition receptors (PRRs), and which types do keratinocytes express?

Answer 17

PRRs detect pathogen-associated molecular patterns (PAMPs). Keratinocytes express TLRs, NOD-like receptors, RIG-1-like receptors, and C-type lectins.

Question 18

What are β-defensins, and what is their role in skin immunity?

Answer 18

Antimicrobial peptides (AMPs) produced by keratinocytes. Kill bacteria by disrupting their membranes.

Question 19

What are Langerhans cells, and what is their role in the skin?

Answer 19

Dendritic cells in the epidermis. Promote Th17 responses against extracellular pathogens. Help regulate immune tolerance to nonpathogenic antigens.

Question 20

What is cutaneous leukocyte antigen (CLA), and what does it do?

Answer 20

Adhesion molecule on skin-homing T-cells. Binds to E-selectin on blood vessel endothelium to guide T-cells to the skin.

Question 21

How do inflammatory responses in the skin affect immune cell migration?

Answer 21

More leukocytes are recruited (e.g., neutrophils, monocytes, eosinophils). Increases vascular permeability to allow immune cells to exit the blood.

Question 22

What are M-cells, and what is their role in gut immunity?

Answer 22

Specialized epithelial cells in Peyer’s patches. Transport antigens from the gut lumen to APCs.

Question 23

What happens after antigen uptake by M-cells?

Answer 23

Dendritic cells activate T and B lymphocytes in Peyer’s patches. Lymphocytes travel to mesenteric lymph nodes for further activation.

Question 24

What is the function of retinoic acid in gut immune responses?

Answer 24

Produced by CD103+ dendritic cells. Induces T-cells to upregulate LPAM-1 (α4β7 integrin) and CCR9 for gut homing.

Question 25

What is LPAM-1 (α4β7 integrin), and what is its function?

Answer 25

Adhesion molecule on gut-homing T-cells. Binds to MAdCAM-1 on intestinal lamina propria postcapillary venules.

Question 26

How does gut-homing of T-cells occur?

Answer 26

Activated T-cells enter the bloodstream via the thoracic duct. They express LPAM-1 (α4β7) and CCR9, which guide them to the gut lamina propria.

Question 27

What are intraepithelial lymphocytes (IELs), and where are they found?

Answer 27

Specialized T-cells located between epithelial cells in the gut. Express αEβ7 integrin, which binds E-cadherin to localize them in the epithelium.

Question 28

What are the two main types of IELs?

Answer 28

αβ TCR IELs → Most are CD8+, some are CD4+. γδ TCR IELs → Recognize stress signals rather than peptides.

Question 29

What is unique about CD8 αα T-cells in the gut?

Answer 29

Express CD8 αα homodimer (instead of the conventional CD8 αβ). Found only in IELs, and they do not require MHC class I for activation.

Question 30

What are MIC proteins (MICA/MICB), and how do they function in gut immunity?

Answer 30

Stress-induced molecules expressed on intestinal epithelial cells. Recognized by γδ TCR IELs to trigger rapid immune responses.

Question 31

How do regulatory T-cells (Tregs) help maintain gut homeostasis?

Answer 31

Secrete IL-10 and TGF-β to prevent excessive immune responses. Promote tolerance to commensal bacteria.

Question 32

How do immune cells home to the lungs?

Answer 32

CXCR3+ T-cells are attracted by CXCL10 in the lungs. CCR5+ T-cells are attracted by CCL5 in the lungs.

Question 33

How do immune cells home to different mucosal tissues?

Answer 33

Specific homing receptors interact with HEV addressins in different tissues. Chemokines (e.g., CXCL10, CCL5) direct immune cell migration.

Question 34

Where are naive T and B cells activated?

Answer 34

In secondary lymphoid organs such as lymph nodes and spleen.

Question 35

What are the two main zones of a lymph node?

Answer 35

The cortex (B cell zone) and the paracortex (T cell zone).

Question 36

What is the function of a germinal center?

Answer 36

It is the site within follicles where B cells proliferate, undergo somatic hypermutation, and class-switch.

Question 37

Is the follicle the same as the B cell zone?

Answer 37

Yes, the follicle is where B cells are concentrated.

Question 38

What is HEV in lymph nodes?

Answer 38

High endothelial venule; specialized blood vessels for lymphocyte entry into lymph nodes.

Question 39

What are FRCs?

Answer 39

Fibroblastic reticular cells that form a conduit system and secrete chemokines to organize T cell zones.

Question 40

What are IDC or DC?

Answer 40

Interstitial dendritic cells or dendritic cells that present antigen to T cells.

Question 41

What is the red pulp of the spleen?

Answer 41

Region rich in blood-filled vascular sinusoids; removes aged or opsonized blood cells.

Question 42

What is the white pulp of the spleen?

Answer 42

Lymphocyte-rich region for adaptive immune responses to blood-borne antigens.

Question 43

What is the role of stromal cells in lymphoid organs?

Answer 43

They produce chemokines and cytokines to guide lymphocyte positioning.

Question 44

What is the role of the spleen in immunity?

Answer 44

Filters blood, removes damaged cells, and initiates immune responses to blood-borne antigens.

Question 45

How do antigens enter lymph nodes?

Answer 45

Via afferent lymphatic vessels.

Question 46

What are high endothelial venules (HEVs) specialized for?

Answer 46

Allowing naive lymphocytes to enter lymph nodes from the bloodstream.

Question 47

What is a primary follicle?

Answer 47

A B cell zone without a germinal center.

Question 48

What is a secondary follicle?

Answer 48

A follicle that contains a germinal center.

Question 49

What happens in germinal centers?

Answer 49

B cells undergo proliferation, somatic hypermutation, and class-switching.

Question 50

How do naive T cells find antigen?

Answer 50

They scan APCs like dendritic cells in T cell zones.

Question 51

How do naive B cells find antigen?

Answer 51

They bind unprocessed antigen or capture it via complement receptors.

Question 52

What is opsonization?

Answer 52

The coating of microbes with antibodies or complement to enhance phagocytosis.

Question 53

What is the function of complement?

Answer 53

A system of proteins that enhances immunity through lysis, opsonization, and inflammation.

Question 54

What are immunologically privileged sites?

Answer 54

Body areas where immune responses are limited (e.g., brain, eye, testis).

Question 55

How are privileged sites protected?

Answer 55

Blood-tissue barriers, low complement levels, FasL, and immunosuppressive cytokines.

Question 56

What is FasL?

Answer 56

A ligand that induces apoptosis in Fas-expressing immune cells.

Question 57

What cytokines are immunosuppressive?

Answer 57

TGF-beta, IL-10.

Question 58

What is the conduit system in lymph nodes?

Answer 58

A collagen network used to transport small antigens and chemokines.

Question 59

What type of vessels drain lymph from lymph nodes?

Answer 59

Efferent lymphatic vessels.

Question 60

What is the role of dendritic cells?

Answer 60

To capture and present antigens to naive T cells.

Question 61

What is the purpose of class switching?

Answer 61

To produce antibodies of different isotypes (e.g., IgG, IgA) with the same specificity.

Question 62

What triggers B cell activation?

Answer 62

Antigen binding and T cell help.

Question 63

What triggers T cell activation?

Answer 63

Recognition of antigen-MHC complex on APCs.

Question 64

What is the role of macrophages in the spleen?

Answer 64

To phagocytose opsonized or damaged red blood cells and microbes.

Question 65

How are antigens delivered to the spleen?

Answer 65

Through the bloodstream, especially via splenic artery.

Question 66

Where are T cells primarily found in the spleen?

Answer 66

In periarteriolar lymphoid sheaths (PALS).

Question 67

Where are B cells primarily found in the spleen?

Answer 67

In follicles and marginal zones.

Question 68

How do lymphocytes enter lymph nodes?

Answer 68

Via HEVs in the paracortex.