Sarkis K Mazmanian, California Institute of Technology
34
Sarkis K Mazmanian, California Institute of Technology
Transcript of Sarkis K Mazmanian, California Institute of Technology
Sarkis K Mazmanian, California Institute of Technology
•The human gut harbors 1011-1012 bacteria per gram colonic content
(>1014 total bacteria)
•Total bacteria outnumber human cells 10:1
•Total bacterial genes outnumber human genes >100:1
•>1,000 different species of bacteria are resident in the human
intestinal microbiota (400-500 per person)
The human microbiota
Lee & Mazmanian, Science (2010)
•Antibiotics ameliorate symptoms in
humans and animals
•Germ-free animals do no develop IBD
in several models
•No definitive pathogens identified
•Immune reactivity to commensal
organisms
•Alterations in the microbiota of IBD
patients
•Predicted defects in immune regulation
Bacteria play a critical role in
inflammatory bowel disease (IBD)
The human gastrointestinal tract is
populated by both harmful and beneficial bacteria
Pederson D, Cell Host & Microbe (2008)
•Bacteroides fragilis is a gram-negative, obligate anaerobic bacteria
•B. fragilis synthesizes at least eight unique capsular
polysaccharide complexes from distinct genomic loci
•At least two of these polysaccharides (PSA and PSB) have a
novel zwitterionic structure (both a positive and negative charge
within each repeating subunit)
•B. fragilis is a prominent commensal of in the human GI tract
Polysaccharide A (PSA)
Mazmanian et al, Cell (2005)
PSA protects from chemically induced
intestinal inflammation
Mazmanian et al, Nature (2008)
Colitis is driven pro-inflammatory T-helper cells and
elevated IL-17/IL-23 levels
Neurath, M, Nature Medicine (2007)
Colitis
PSA mediates the expansion of functionally suppressive
CD4+CD25+Foxp3+ Tregs during TNBS colitis
Round et al., PNAS (2010)
Protection from TNBS colitis by PSA requires
Toll-like receptor 2 signaling
PSA is packaged into outer membrane vesicles (OMVs)
Shen et al., (submitted)
OMVs protect mice from colitis in a PSA-dependent manner
OMVs protect mice from colitis in a PSA-dependent manner
Gene expression profile of PSA-specific and TLR2
dependent genes in dendritic cells
Gadd45a expression in dendritic cells is required for PSA-
mediated protection from colitis
Gadd45a expression in dendritic cells is required for PSA-
mediated protection from colitis
PSA of B. fragilis prevents pro-inflammatory immune
responses in the gut to protect from colitis
Gadd45a
PSA of B. fragilis prevents pro-inflammatory immune
responses in the gut to protect from colitis
Gadd45a
Is there a role for PSA during homeostasis?
Conventional Germ-free B. fragilis B. fragilisPSA
CD
4
IL17A
7.65 0.73 1.46 4.48
% C
D4
+IL
-17A
+ 15
10
5
0 0
5
10
15 *** ***
Round et al., Science (2011)
PSA restrains Th17 responses to B. fragilis
Foxp3
CD
4
1.99 0.06
-DT +DT
0
1
2
3
4
5
6
7
- DT +DT
*** 10
5
0 IL-17A
CD
4
21 3.1 37 6.2
-DT +DT (-Tregs)
0.7 0.9
% IL
-17A
+
Foxp3-DTR mice with B. fragilis
Conventional Germ-free B. fragilis B. fragilisPSA
CD
4
IL17A
7.65 0.73 1.46 4.48
% C
D4
+IL
-17A
+ 15
10
5
0 0
5
10
15 *** ***
Round et al., Science (2011)
PSA restrains Th17 responses to B. fragilis
Foxp3
CD
4
1.99 0.06
-DT +DT
0
1
2
3
4
5
6
7
- DT +DT
*** 10
5
0 IL-17A
CD
4
21 3.1 37 6.2
-DT +DT (-Tregs)
0.7 0.9
% IL
-17A
+
Foxp3-DTR mice mono-colonized with B. fragilis
Toll-like receptors on innate cells activate T cells
Toll-like receptors on innate cells activate T cells
TLR2 expression on CD4+ T cells is required for
in vitro IL-10 production by PSA
TLR2 expression on CD4+ T cells is required for
in vitro IL-10 production by PSA
PSA is required for efficient mucosal colonization
of germ-free mice by B. fragilis
Germ-free
B. fragilis
mono-colonized B. fragilis
mono-colonized
rel. u
nits
a
CF
U/g
1010
106
102
Colon Lumen
PSA is required for efficient mucosal colonization
of germ-free mice by B. fragilis
Germ-free
B. fragilis
mono-colonized B. fragilis
mono-colonized
re
l. u
nits
-DT +DT
(-Tregs)
10
5
0
15
1,0E+00
1,0E+01
1,0E+02
1,0E+03
1,0E+04
1,0E+05
1,0E+06
1,0E+07
1,0E+08
1,0E+09
1,0E+10
1,0E+11
CF
U
-DT +DT
Colon Lumen
Germ-free mice with B. fragilis
PSA signals through TLR2 on Tregs to suppress Th17 cell
responses during mucosal colonization by B. fragilis
Iso α-IL-17A
rel. u
nits
Iso α-IL-17A 1.01003
1.01004
1.01005
1.01006
1.01007
1.01008
108
106
104
30
20
10
0
re
l. u
nits
-DT +DT
(-Tregs)
10
5
0
15
1,0E+00
1,0E+01
1,0E+02
1,0E+03
1,0E+04
1,0E+05
1,0E+06
1,0E+07
1,0E+08
1,0E+09
1,0E+10
1,0E+11
CF
U
-DT +DT
Colon Lumen
B. fragilis
B. fragilis
PSA
WT CD4+ Tlr2-/- CD4+ 0
5
10
15
20
25
30
35
40
rel. u
nits 40
50 Colon
CF
U/g
Colon
Germ-free mice with B. fragilisPSA
Germ-free mice with B. fragilis
PSA signals through TLR2 on Tregs to suppress Th17 cell
responses during mucosal colonization by B. fragilis
PSA evolved to promote mucosal tolerance during
commensal colonization by Bacteroides fragilis
TLR2
WT B. fragilis
Gadd45a
PSA evolved to promote mucosal tolerance during
commensal colonization by Bacteroides fragilis
TLR2
WT B. fragilis
B. fragilisPSA
Bach JF, NEJM, 2002
The inverse correlation between infectious diseases
and human inflammatory disorders
Bach JF, NEJM, 2002
The inverse correlation between infectious diseases
and human inflammatory disorders
Bach JF, NEJM, 2002
The inverse correlation between infectious diseases
and human inflammatory disorders
Regulatory T cells protect against these diseases in mice
Potential causes of dysbiosis due to ‘western’ lifestyles
its role in intestinal health and disease
Genetics and Environment
Round & Mazmanian, Nature Rev Immunol (2009)
June Round (Utah) Yue Shen Janet Chow Melanie Lee Jennifer Li Yun Kyung Lee Arya Khosravi Haiqing Tang Huitung Chu Gil Sharon Sara McBride Katie Schretter Gregory Donaldson Talal Chatila (UCLA) Bana Jabri (UChicago) Jonathan Ashwell (NIH) Alexander Rudensky (MSKCC) Lora Hooper (UT Southwestern)
