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Immunology Flashcards

1
Q

Transcellular vs Paracellular transport

A

Paracellular transport involves transfer of substance across epithelium through an intercellular space between cells. This is in contrast to transcellular which is through the cell

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2
Q

Mucosal tissues of the human body

A

Lacrimal gland, salivary gland, mammary gland, kidney, urogenital tract (kidney, uterus, vagina, bladder), conjunctiva, oral cavity, sinus, trachea, oesophagus, lungs, stomach, intestine

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3
Q

Primary lymphoid tissue

A

Bone marrow and Thymus

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4
Q

Secondary lymphoid tissue

A

Spleen, Peyer’s patch in small intestine, adenoid, tonsil

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5
Q

What does the paracortical area of lymph node consist

A

Mainly T-cells

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6
Q

Primary lymphoid follicles in lymph node

A

Lymphoid follicles without germinal center. Secondary lymphoid follicles contain a germinal center (mainly with B cells)

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7
Q

Is there active upregulation/downregulation of immune system in GI tract

A

Active downregulation by inhibitory macrophage and tolerising dendritic cells, important in preventing Chrons and Ulcerative Colitis

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8
Q

What are peyers patches

A

Small masses of lymphatic tissue found throughout the Ileum region of small intestine. They monitor bacteria ad prevent growth of pathogens in the small intestine

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9
Q

Specialized epithelial cells with an immune function

A

M cells, transport antigens from lumen to cells in the Peyer’s patches. They have membrane ruffles (microvilli) to increase surface area. Dendritic cells are also closely associated with these M cells.

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10
Q

Why do Peyer’s patch shown up as bright purple in histological stains

A

Due to the presence of lymphocytes. They are inactivated and hence have small cytoplasm.

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11
Q

Process of T cell activation by M cells

A

M cells take up antigen via phagocytosis or endocytosis. Antigen is transported across M cells in vesicles and released at basal surface. Dendritic cells take up this antigen, which activate T cells.

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12
Q

Can dendritic cell process extend into the lumen across the epithelial layer

A

Yes, to capture antigen from the gut

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13
Q

Immune cells of GI tract epithelium

A

CD8+ T cells and Dendritic Cells

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14
Q

Immune cells of lamina propria of GI tract

A

CD4 + T cells, Macrophage, Mast cells, Dendritic cell, IgA and Plasma cell

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15
Q

Receptors for T cell entry to Payer’s patches from vessel

A

CCR7 and L-Selectin

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16
Q

Process of T cell entry into the gut

A

T cells enter Payer’s patch from blood vessel directed by homing receptor CCR7 and L-Selectin. T cells encounter antigen transported across M cells and become activated by dendritic cells. Activated T cells drain via mesenteric lymph nodes to thoracic duct and return to gut via blood stream.

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17
Q

Protein expressed on endothelial cells of the blood vessels that bind to effector T cells

A

Addressin or MAdCAM-1 is a protein which are ligands to homing receptors of lymphocytes. Once in the endothelium, gut epithelial cells secrete cytokines specific for gut-homing T cells

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18
Q

Divide the mucosal immune system into inductive and effector sites.

A

Inductive sites are collectively called Mucosa-Associated Lymphoid Tissue (MALT). These include Gut Associated Lymphoid Tissue (GALT), Nasopharyngeal-Associated Lymphoid Tissue (NALT) and lymphoid sites. Effector sites can be the lamina propria region of GI tract, upper respiratory tract and reproductive tracts

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19
Q

What is Addressin commonly known as

A

MAdCAM-1 protein

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20
Q

What is gut specific homing

A

Mechanism by which activated T-cells and antibody secreting cells are targeted to inflamed and non-inflamed regions of the gut

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21
Q

What type of memory cells are induced by orally administered antigens

A

Memory cells that express the Integrin Alpha4-Beta7

22
Q

What do inductive sites do

A

Provide a continuous source of memory B and T cells that can circulate around the body and move into effector sites

23
Q

Dominant antibody in humoral intestinal response

A

IgA (80%), IgM (15%) and IgG (5%)

24
Q

How does IgA get into the gut lumen

A

IgA secreting cells secrete IgA. This binds to secretory component at its J-chain. The IgA binds to a receptor on the basolateral face of epithelial cell. This undergoes endocytosis , then transcytosis to apical face of epithelial cell. The IgA is then released into the lumen

25
Q

Functions of IgA in gut lumen

A

1) Secreted IgA can bind and neutralize pathogens and toxins
2) Can bind and neutralize pathogens in endosomes \
3) Export toxins and pathogens from lamina propria while being secreted

26
Q

What are intraepithelial lymphocytes

A

CD8+ T cells found in the epithelial layer of mammalian mucosal lining such as GI tract. However, they do not need priming and release cytokines causing killing of infected target cells as soon as encounter an antigen

27
Q

What does elevation of intraepithelial lymphocytes show

A

This indicates ongoing inflammation in the mucosa. Can also be a marker for neoplasia

28
Q

Advantage of intraepithelial lymphoctyes

A

Detect antigen and kill infected cell without affecting surrounding cells. Helps prevent spread and protects undamaged cells

29
Q

Why do we get flattened epithelium in coeliac disease

A

In coeliac disease, there is more killing of cells by intraepithelial lymphocytes than growth of epithelial cells. This leads to a flattened epithelium and lesser absorption of nutrients.

30
Q

How do activated intraepithelial lymphocytes kill infected cells

A

By perforin/granzymes and Fas-dependant ligand

31
Q

Patients with IgA deficiency are symptomatic

A

False, IgM can replace IgA in its function albeit with lesser efficiency

32
Q

What helps regulate local hyporesponsiveness

A

Commensal organisms via PPAR gamma

33
Q

How do T cells take part in mucosal hyporesponsiveness

A

T helper 3 cells produce transforming growth factor (TGF)-Beta that is an immunosuppresant. Also induces switching of B cells to IgA production

34
Q

How do dendritic cells take part in mucosal immune suppression

A

Commensal bacteria, production of transforming growth factor (TGF), Prostaglandin E2 and TSLP inhibit dendritic cell maturation. These give weak co-stimulatory molecules to CD4 T cells to differentiate into regulatory Th3 and Treg cells. Invasive microorganisms that penetrate epithelium activate dendritic maturation that express strong co-stimulatory molecules and induce differentiation into effector Th1 and Th2 cells.

35
Q

Process of mucosal response to infection

A

Bacteria are endocytosed and recognized by Toll-like receptors in intracellular vesicles or bacteria and their products entering the cytoplasm are recognized by NOD1 and NOD2. This leads to gene transcription and production of cytokines, chemokines and defensins.

36
Q

How are viruses shuttled from dendritic cells to the bloodstream

A

Selective infection by viral strain. Fusion of dendritic cell and CD4+ lymphocyte. Transport of virus bound dendritic cell to regional lymph node. Spread of infection to activated CD4+ lymphocyte. Entry of virus-infected cells into bloodstream. Widespread dissemination

37
Q

What is Common Variable Immune Deficiency (CVID)

A

Primary immunodeficiency with recurrent sinopulmonary and GI infections due failure to differentiate into Ig secreting cells. This leads to low levels of antibody in the blood and less antigen specific response

38
Q

What is X-linked Agammaglobulinemia (XLA)

A

B cells aren’t generated leading to a lack of protein called gamma globulins including antibodies. Leads to sinopulmonary and GI infections along with devastating systemic manifestations of chronic enterovirus infection

39
Q

What is Chronic Granulomatous Disease

A

Immune system can’t form a reactive oxygen species, superoxide radical due to defective phagocyte NADPH oxidase used to kill ingested pathogens. Can lead to interstitial granulomas, liver abscess, perianal abscess and skin abscess

40
Q

What is Severe Combined Immunodeficiency

A

Disturbed development of B and T cells. Most severe form of primary immunodeficiency. Recurrent infection

41
Q

How is food allergy mediated

A

Type 1 hypersensitivity reaction initiated by crosslinking of allergen-specific IgE on surface of mast cells with specific allergen.

42
Q

Response to systemic anaphylaxis

A

Oedema, increase vascular permeability, laryngeal oedema, circulatory collapse and death

43
Q

How is gluten sensitivity triggered

A

Gamma interferon from gluten-specific T cell activate epithelial cells which produce IL-15 which induces proliferation and activation of intraepithelial lymphocytes. These IEL and T cells kill epithelial cell via cytokine release

44
Q

Gold standard for diagnosins coeliac disease

A

Biopsy. Serology to test for IgA anti-tissue transglutinamase autoantibodies

45
Q

What does usefulness of serology depend upon

A

Dietary state of patient, no gluten then no autoantibody

46
Q

Treatment for X-linked agammaglobulinaemia

A

Administer immunoglobulins

47
Q

Treatment for Chronic Granulomatous Disease

A

Bone marrow transplant

48
Q

How is coeliac diseas diagnosed in children

A

Non-biopsy diagnosis

49
Q

What is Crohns disese

A

Discontinuous inflammation with deep and eroding tissue fissures with or without granulomas

50
Q

What causes Crohns disease

A

Genetic susceptibility but requires a trigger. Inflammation and granulomas mediated by T-helper cells 1, Interleukin-12, Tumour Necrosis Factor-Alpha and Gamma Interferon

51
Q

What is Ulcerative Colitis

A

Inflammation and ulceration of rectum upwards to colon. Crypts get distorted with infiltration of monocytes/neutrophils and plasma cells.

52
Q

Treatment of coeliac disease

A

Immunosuppressants and non-specific anti-inflammatory drugs such as Steroids/Azathioprine/Cyclosporin and Methotrexate. Also administer anti-TNF alpha

GI (32 decks)

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