Host Microbe Interactions

Question 1

skin: as a physical barrier

Answer 1

tightly packed highly keratinised cells

constant renewal and replacement

Question 2

skin: physiological barriers

Answer 2

low pH of 5.5

low oxygen tension

Question 3

skin: sebaceous glands as barriers

Answer 3

secrete hydrophobic oils

lysozyme that destroys the structural integrity of bacterial cell walls

ammonia has anti bacterial properties

anti-microbial peptides eg defensins secreted by keratinocytes

Question 4

what are the physical defences in the mucosa of the resp/GI tract

Answer 4

antimicrobial substances eg lysozyme

secretory IgA

gastric acid

Question 5

what bug do mast cells target

Answer 5

worms

Question 6

how can fungal infections impair the skin barrier

Answer 6

eg tinea pedis

cause cracking of teh skin

Question 7

what cells are phagocytes

Answer 7

• neutrophils and macrophages
• they are capable of engulfing bacteria and killing via oxygen in/dependent mechanisms

Question 8

what bug do phagocytes target

Answer 8

bacteria and fungi

Question 9

what are macrophages derived from

Answer 9

monocytes that have matured in the tissues

Question 10

which bugs do T lymphocytes protect against

Answer 10

viruses, fungi and protozoa

Question 11

helper CD4+ T cells

Answer 11

activate phagocytes to kill microbes

• TH1 activate macrophaes to destroy micro organisms
• TH2 activate B cells to rpoduce plasma cells which produce antibodies

Question 13

effector cytokines of Th1 cells

Answer 13

IF gamma and IL 2

Question 14

effector cytokines of TH2 cells

Answer 14

IL 4-6

Question 15

HIV infection

Answer 15

• infects CD4+ T cells producing a progressive decline in their numbers
• this results in a deficinecy in cell mediated immunity

Question 16

which disease is there a particularly high risk of in HIV, and how does CD4 count influence this

Answer 16

• invasive pneumococcal disease (S. Pneumoniae)
• irrespective of CD4
• eg bacteraemia, meningitidis, empyema etc

Question 17

when is the pneumonoccal vaccine received: UK VACCINATION SCHEDULE

Answer 17

• 2 months
• 4 months
• withia a year of 1st birthday
• 65y

Question 18

discuss the diseases that one is susceptible to with HIV, influenced by their CD4 count

Answer 18

• CD4 <350: TB, candidiasis
• CD4 <200: Pneumocystic jirovecii, Toxoplasma gondii
• CD4 <100: CMV

Question 19

name 3 herpesviruses

Answer 19

CMV, HIV, EBV

Question 20

what are the classical characteristics of herpesviruses

Answer 20

cause recurring, latent infections

Question 21

CMV

Answer 21

• clinically very similar to glandular fever
• causes atypical pneumonia, granulomatous chorioretinitis

Question 22

which viruses have a risk of feotal damage and congenital infection

Answer 22

toxoplasmosis and CMV

Question 23

toxoplasmosis

Answer 23

• Protozoan parasite of cats that is transmitted to humans through undercooked meat or contact with cat litter

Question 24

toxoplasmosis infection clinically

Answer 24

similar to glandular fever

can cause granulomatous chorioretinits, and can be sight threatening if it affects the macula

Question 25

causes of hyposplenism

Answer 25

* splenectomy * functional * sickle cell disease * cirrhosis * coeliac

Question 26

what is one particuarly susceptible to if they have hyposplenism

Answer 26

invasive infection from encapsulated organisms * *Streptococcus pneumoniae* (pneumococcus) * *Haemophilus influenzae* type B (HiB) * *Neisseria meningitidis* (meningococcus) risk can be reduced by vaccination, preferably before splenectomy etc

Question 28

why are elderly people more prone to infection

Answer 28

* They are less able to distinguish self from non-self, and so are at a greater risk of autoimmune disease * Phagocytes destroy bacteria and antigens more slowly * T cells respond more slowly * Less antibody is produced, and it binds to antigen less well * Less complement is produced

Question 29

what is the aim of immune suppression

Answer 29

* create a blunt immune response * reduce damage done due to immune system as a result of autoimmunity * to prevent transplant rejection

Question 30

how does infection present in IC people

Answer 30

differently * absence of fever * lack of inflammatory response * non specific, non localising features

Question 31

immunosuppression: what can steroids cause in particular

Answer 31

fungal infections

Question 32

immunosuppression: anti-TNF alpha therapies

Answer 32

can reactivate latent TB fungal infections - particularly Aspergillus

Question 33

immunosuppression: what can purine analogues cause

Answer 33

viral infections (HSV and VZV in particular) pneumocystis jirovecii

Question 34

what is used as prophylaxis in HIV

Answer 34

co-trimoxazole

Question 35

what is used as prophlaxis in a bone marrow transplant

Answer 35

antifungal agent - itraconazole