13. Autoimmune diseases

Question 1

Autoimmune haemolysis

Answer 1

Example of molecular mimicry

after Mycoplasma pneumoniae
Mycoplasma antigen has homology to ‘I’ antigen on red blood cells
IgM antibody to mycoplasma may cause transient haemolysis

Question 2

Rheumatic fever

Answer 2

Example of molecular mimicry

inflammatory disease occurring after streptococcal infection affecting heart, joints, skin and brain
Anti-streptococcal antibodies believed to cross-react with connective tissue

Question 3

Evidence of T1DM

Answer 3

• HLA Associations (T cell mediated)
• can detect islet cell antibodies before onset of clinical disease
• CD8/CD4 pancreatic infiltration

Question 4

Outline the process of indirect immunofluorescence

Answer 4

looks for antibodies in blood

Patient serum containing (or not) relevant antibodies

Add detection antibody labelled with fluorescent marker

Look for fluorescence under microscope

Question 5

direct immunofluorescence

Answer 5

looking antibodies in tissue biopsy

Question 6

Pemphigoid

Answer 6

Bullous skin disease

Thick-walled bullae, rarely on mucus membranes

Fulfils criteria for antibody-mediated disease

Target is antigen at dermo-epidermal junction

Question 7

Pemphigus

Answer 7

Bullous skin disease
Thin-walled bullae on skin and mucus
membranes, rupture easily
Fulfils critiera for antibody-mediated disease
Target is the intercellular cement protein desmoglein 3 in superficial skin layers

Question 8

Pernicious anaemia

Answer 8

Autoimmune destruction of gastric parietal cells

Loss of intrinsic factor abrogates B12 absorption

Question 9

Plasmapharesis

Answer 9

removes antibodies from the bloodstream therefore may be useful in antibody-mediated diseases

Question 10

How do they diagnose Coeliac disease

Answer 10

Indirect immunofluorescence
-tissue transglutaminase

-HLA typing- absence of HLA-DQ 2 and 8 makes coeliacs very rare