Lecture #2

Question 1

First line of defense 3 mechanisms

Answer 1

1. Physical barriers: skin, mucous membranes, secretions
2. Cells: Macrophages, mast cells, endothelial cells, DC, ILC, MAIT (mucosal associated variant T), iNKT, gamma/delta T cells
3. Molecules: soluble antimicrobial peptides, natural autoantibodies, complement proteins

Question 2

Soluble anti microbial molecules (3 examples)

Answer 2

1. Defensin- direct cytotoxicity
   Secreted from salivary glands, paneth cells, leukocytes
   Amphipathic molecule forming a hole in the membrane of the microbe.
2. Lysozyme- enzymatic destruction
   Secreted from salivary glands and lacrimal glands
   Peptidoglycan N acetylmuramoyl hydrolase
3. Calprotectin- deprivation of bacterial nutrients by metal sequestration (chelation) of Mn2+ and Zn2+

Question 3

Professional phagocytes

Answer 3

Neutrophils:
Always infiltrated upon pathogen exposure
1. Phagocytosis intra vesicular killing
2. Degranulation (frustrated phagocytosis) extra cellular digestion
3. NETosis extra cellular DNA trap

Macrophages

1. Residual macrophages in the tissues (Kupffer cells, osteoclasts, microglia, histiocytes)
2. Infiltrated macrophages
   - Classically activated M1 secrete proinflammatory cytokines activated by INF gamma from Th1 and PAMP/DAMP
   - Alternatively activated M2 secrete supressive anti inflammatory cytokines activated by apoptosis and IL4, IL13 from Th2

Question 4

Macrophages effector functions

Answer 4

Upon phagocytosis and activation 3 destruction mechanisms can occur in macrophages
1. Lysosomal enzymatic degradation
2. O2 dependent respiratory burst (production of ROS)
The enzyme required is NADPH oxidase, deficiency of this enzyme will cause chronic granulomatous disease
3. NO mediated killing (iNOS)

Question 5

Signals for apoptosis and tolerance

Answer 5

1. “find me” signal for macrophages (IL8 and MCP1)
2. “eat me” signal on apoptotic bodies is outer leaflet phosphatidyl serine
3. “tolerate me” signal by secreting IL10, TGF beta, PGE2

Question 6

Dendritic cells (mature and immature)

Answer 6

Immature DC: reside in peripheral tissues and have high phagocytic activity
upon phagocytosis they migrate to regional lymph nodes and become mature
Mature DC: found in the deep cortex of the lymph node , low phagocytic activity and serve as APCs for lymphocyte activation

Question 7

Structurally adaptive but functionally innate cells

Answer 7

Innate lymphoid cells ILC, NKC

Question 8

ILC innate lymphoid cells

Answer 8

Derived from common lymphoid progenitor donor,
DO NOT have TCR
But secrete the same cytokines as their equivalent T cells
1. Type I - like Th1 secrete IFN gamma
2. Type II - like Th2 secrete IL10, IL4, IL5
3. Type III - like Th17, Th22 secrete IL17, IL22

Question 9

NKC natural killer cells

Answer 9

Large granular lymphocytes
DO NOT have TCR/BCR
Kill tumor cells, virus infected cells by apoptosis (granzymes+perforins and FasL)

Question 10

NKC receptors

Answer 10

1. NKC identify the “missing self” by dual receptor system
   KIR/KAR

KAR (NKG2D): killer activator receptor
recognizes MHCI like molecules on the surface of the cells (MICA, MICB, ULBP1,2,3)
KIR (NKG2A): killer inhibitor receptor
recognizes MHCI on the surface of the cells

When only KAR binds to its ligand - killing is induced
When both KIR and KAR are bound - no killing is induced

2. ADCC antibody dependent cellular cytotoxicity
   Induced by binding of Fc gamma RIIIA to an IgG bound to an Ag on a target cell

Question 11

Receptors on phagocytes

Answer 11

PRRs

Opsonic - complement receptors, FcR (Fc gamma R)

Question 12

PRRs have 3 forms

Answer 12

1. Membrane bound (SR, MR, CompR, TLR)
2. Intracellular (RIG1, NOD/NLR)
3. Secreted (ficolins, lung surfactant, MBL, pentraxins)

Question 13

Signals required for the activation of the natural immune system (for eg of DC)

Answer 13

First signal: PAMP binding to TLR will induce NFkappaB - will induce the synthesis of pro IL1 beta, pro IL18.

Second signal: DAMP binding to PRR will induce inflammosome complex - activate pro caspase 1 to caspase 1 - activate pro IL1 beta and pro IL18 to IL1 beta and IL18.

Question 14

Structure of inflammosome

Answer 14

NLRP3
ASC
pro caspase 1

Question 15

Auto inflammatory disorders

Answer 15

1. Muckle Wells syndrome NLRP3 deficiency
2. PAPA syndrome “pyogenic arthritis with pyoderma and acne” no activation of NLRP3 and ASC
3. HIDS “hyper immunoglobulinemia D with periodic fever syndrome” no activation of caspase1
4. DIRA “deficiency in IL1R antagonist”