Host-Microbe Interaction

Question 1

Initial immune protection is provided by what?

Answer 1

Physical barriers

Question 2

What are the two main components of the immune system?

Answer 2

Innate (phagocytes / NK cells)

Acquired/adaptive (B cells / T cells)

Question 3

Bacteria are controlled by what immune cells?

Answer 3

Phagocytes
B lymphocytes and antibodies
Complement

Question 4

Fungi are controlled by what types of immune cells?

Answer 4

Phagocytes
T-lymphocytes
Eosinophils

Question 5

Viruses are controlled by what types of immune cells?

Answer 5

T and B lymphocytes

Question 6

Protozoa are controlled by what groups of immune cells?

Answer 6

T lymphocytes

Eosinophils

Question 7

Worms are controlled by what 2 types of immune cell?

Answer 7

Mast cell

Eosinophils

Question 8

What properties does the skin have which make it suitable as a physical barrier to infection?

Answer 8

Keratinocytes secrete antimicrobial peptides (defensins)

Sweat glands secrete microbe-inhibiting substances (e.g. fatty acids)

Antigen-presenting cells in skin

Question 9

The mucous membranes of the Respiratory/GI/GU tracts contain which properties that make them suitable physical barriers to infection?

Answer 9

Antimicrobials e.g. lysozyme
IgA
Gastric acid

Question 10

What disease processes can cause the skin to be an impaired physical barrier to infection?

Answer 10

• Eczema, psoriasis, erythroderma
• Tinea pedis / cracking of skin
• Ulcers / pressure sores

Question 11

What lung diseases can impact the efficiency of the respiratory tract mucous as a physical barrier to infection?

Answer 11

• Cystic fibrosis / Bronchiectasis (impaired mucus clearance)
• COPD
• Poor swallow (neurological illness, e.g. stroke)

Question 12

What diseases can affect the ability of the GI tract mucosa to be a suitable physical barrier to infection?

Answer 12

• Mucositis secondary to chemotherapy
• IBD
• Bowel cancer

Question 13

What WBCs are the main types of phagocyte?

Answer 13

Neutrophils and macrophages

Question 14

In what conditions would a patient be deficient in phagocytes?

Answer 14

• Haematological malignancy (e.g. acute leukaemia)

- Cytotoxic chemotherapy

Question 15

Describe the difference between CD4 and CD8 T cells

Answer 15

CD4 activate phagocytes to kill pathogen

CD8 Directly kill pathogen

Question 16

What diseases cause a deficiency in T cells?

Answer 16

HIV infection (acquired deficiency in CD4)
Lymphoma
Primary immunodeficiency syndromes (e.g. SCID)

Question 17

What antibody is produced first from B cells, and what antibody is produced most abundantly?

Answer 17

IgM = first (but has weak affinity)
IgG = most abundant (strong affinity)

Question 18

Deficiencies of B cells occur in what diseases?

Answer 18

• Myeloma (plasma cell cancer)
• Primary immunodeficiency syndromes
• Certain immune suppressants (e.g. rituximab)

Question 19

There is a high risk of strep. pneumoniae infection in patients with HIV, regardless of their CD4 count. TRUE/FALSE?

Answer 19

TRUE

Question 20

In HIV, a CD4 count of <350 predisposes to what infections?

Answer 20

Mycobacterium tuberculosis TB

Candidiasis

Question 21

In HIV, a CD4 count of <200 predisposes to what infections?

Answer 21

Pneumocystis jirovecii

Toxoplasma gondii

Question 22

In HIV, a CD4 count of <100 predisposes to what infections?

Answer 22

Cryptococcus neoformans

Cytomegalovirus (CMV)

Question 23

What can lead to hyposplenism?

Answer 23

Splenectomy
=> (trauma, ITP, lymphoma)

”Functional” hyposplenism
=> (sickle cell, cirrhosis, coeliac disease)

Question 24

Patients with hyposplenism are particularly at risk of infection from what types of organisms?

Answer 24

ENCAPSULATED ORGANISMS

• Streptococcus pneumoniae (pneumococcus)
• Haemophilus influenzae type B (HiB)
• Neisseria meningitidis (meningococcus)

Question 25

How can risk of encapsulated organism infection in hyposplenism be reduced?

Answer 25

Vaccinations (particularly before splenectomy if this is the case)

Question 26

Elderly patients are more prone to infections. TRUE/FALSE?

Answer 26

TRUE - Less able to distinguish self from non-self (autoimmune disorders common) - Immune system reacts slower and produces less immune cells

Question 27

What is the main aim of immunosuppressive drugs?

Answer 27

Reduce damage due to the immune response

Question 28

In what ways do immunocompromised patients not respond to infection in the same way as normal patients?

Answer 28

- Fever may be absent - Lack of inflammatory response (CRP / neutrophilia) - Non-specifically unwell (illness not localised)

Question 29

There is often a lower threshold for treatment in patients who are known to be immunocompromised. TRUE/FALSE?

Answer 29

TRUE

Question 30

Steroids are particularly associated with what type of infections?

Answer 30

fungal infections (Candida, Aspergillus)

Question 31

Anti-TNF therapies (infliximab/etanercept) are particularly associated with what types of infection?

Answer 31

Mycobacterium tuberculosis (TB) Fungal infections (Aspergillus)

Question 32

What infections are associated with purine analogue drugs?

Answer 32

Viral infections (Herpes Simplex and Varicella Zoster) Pneumocystis jirovecii

Question 33

In what patients is the risk of infection so high that we would prescribe prophylactic antibiotics?

Answer 33

Co-trimoxazole in patients with HIV Antifungal (e.g. itraconazole) in bone marrow transplant recipient

Question 34

What groups of patients are all eligible for their flu vaccine?

Answer 34

``` PREGNANT WOMEN Chronic heart/lung/kidney/liver disease Immunocompromise Diabetes Aged >65 years ```

Question 35

What groups of patients qualify for a pneumococcal vaccine

Answer 35

``` HYPOSPLENISM Chronic heart/lung/kidney/liver disease Immunocompromise (including HIV infection) Diabetes Aged >65 years ```

Question 36

The Haemophilus influenzae type B (HiB) / DTP/ MMR vaccine is now given to ALL children. TRUE/FALSE?

Answer 36

TRUE

Question 37

What causes the "cytokine storm" of unregulated inflammation in SEPSIS which eventually causes organ dysfunction?

Answer 37

IL-1 TNFa IL-17

Question 38

Why does Lactate rise during SEPSIS?

Answer 38

Tissue hypoxia =>Cells must respirate Anaerobically => lactic acid production

Question 39

Lactate production in sepsis creates a metabolic acidosis with what complication?

Answer 39

Acidosis worsens cardiovascular stability