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STUDY SUMMARY IMMUNOLOGY BASICS
- Course
- Medicine
- Institution
- University Of Cape Town (UCT)
STUDY SUMMARY OF IMMUNOLOGY BASICS FOR MEDICAL STUDENTS
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Immune DeficiencyDefinition Immune Deficiency (ID) = recurrent infections: absence or failure of normal function of >1
elements of the immune system
• Innate / natural immunity ( non-specific)
o 1st line defences
▪ Mechanical ( skin/mucosa)
▪ Biochemical
▪ Normal flora
o 2 line defences
nd
▪ Phagocytes
▪ Complement
• Adaptive immunity ( specific/ acquired)
o T Lc = CMI ( no Ab) – lymphokines ( lymphokines = cytokines)
o B Lc – Hummoral Immunity ( Ab/ Ig)
Note: Ig are synonymous with Ab
Classification of ID
• 1o ID ( born with it)
o Genetically determined
• o
2 ID
o Acquired causes ( HIV/AIDS)
NOTE: 2o ID are more common than 1o
Increased susceptibility to recurrent infections or opportunistic infections (OI)
• Defects in phagocytes ( mainly neutrophils)/ compliment/ Ig
o → recurrent infection with pyrogenic ( pus forming) or extracellular organisms
▪ Bact ( strep pyrogenes, Haemophilis Influenza, Staph Aureus, Strep
pneumonia)
▪ Fungi ( PCP)
• Defects in T Lc ( CMI)
o Recurrent infections with:
▪ Intracellular organisms ( obligate/ facultative)
▪ Opportunistic organisms ( PCP)
NOTE: TB is CMI! + Obligate = cannot grow organism in an artificial medium (e.g. viruses)
Defects in innate immunity
1. Phagocytes
A) Extrinsic
• ↓ prod of Neutrophils
o Congenital aplastic anaemia
, o More common is acquired bone marrow deficiency
▪ Drug induced: chloramphenicol/ cytotoxic drugs ( focus on rapidly producing
cells like hair and mucosa but also affect bone marrow)
• ↓ number of neutrophils
o Destroyed in blood stream,
▪ Cytotoxic drugs
▪ Autoimmune disease ( SLE)
• Defects in chemotaxis
o Failure of neutrophils to arrive at site of infection
o C5a is the most potent chemotaxin
Q: C3a is a more potent chemotaxin than C5a F
B) Intrinsic
1. Chronic granulomatous disease
a. X-linked male ( NB defect in neutrophils)
• Abnormal intracellular metabolism → failure to produce O2 radicals / H2O2 ( hydrogen
peroxidise
• Prone to infections with non pathogen catalase + organism
• Sites ( acute pyrogenic infection): skin ( boils), lungs ( pneumonia), liver ( abscess),
bones(osteomyelitis)
• Dx: NBT ( nitro blue tetrasolium test)
• Presents within the first 2 years of life
NOTE: Staph aureus = catalase +
Streptococci = catalase –
Q: recurrent infections with strep pyrogenes F (only with catalyse +)
2. Chediak Hegashi = abnormal lysosymes
3. Others
2. Compliment ( classical and alternative pathways that meet at C3)
• Defects of initial components
o C1, C4, C2 → Autoimmune Disease ( alternative pathway still functions
▪ NOT prone to recurrent infections but prone to autoimmune disease ( the
classical pathway normally gets rid of immune complexes therefore if
deficiency → type 3 hypersensitivity)
• Defects of C3b/ C3b inhibitors
o → recurrent pyrogenic infections ( C3b is an NB opsonin)
• Defects of terminal components ( C5- C9)
o → marked ↑ in susceptibility to neisseria infections
o Therefore prone to N. Gonorrhoea ( urethral discharge) + meningococcal meningitis
• Deficiency of C1 esterase inhibitor ( can’t control C1 activation)
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