Receptores Toll Like na resposta imune inata

Aula sobre Receptores Toll Like em inglês.

1. Toll-like receptors
Scavenger Receptors
Part of the innate immune response

2. Innate vs. Adaptive Immunity
•Innate Immunity
•Pathogen recognized by receptors
encoded in the germline: pattern
recognition receptors
•Receptors have broad specificity, i.e.,
recognize many related molecular
structures called PAMPs (pathogen-
associated molecular patterns)
•Immediate response
•No memory of prior exposure
•Adaptive Immunity
•Pathogen recognized by receptors
generated randomly: B-cell (BCR) and T-
cell (TCR) receptors for antigen
•Receptors have very narrow specificity;
i.e., recognize a particular epitope after
processing
•Slow (3 -5 days) response (because of the
need for clones of responding cells to
develop)
•Memory of prior exposure

3. Elements of the non-specific (innate) immune system
Anatomical barriers: Skin, Intestinal movement, Oscillation of broncho-pulmonary cilia
Secretory molecules:
•Transferrinand lactoferrindeprive organisms of iron.
•Interferoninhibits viral replication and activates other cells which kill pathogens
•Lysozyme, in serum and tears, breaks down the bacterial cell wall (peptidoglycan)
•Fibronectincoats (opsonizes) bacteria and promotes their rapid phagocytosis.
•Complementcomponents and their products cause destruction of microorganism directly or with the help of
phagocytic cells. Acute phase proteins (such as CRP) interact with the complement system proteins to combat
infections.
•TNF-alphasuppresses viral replication and activates phagocytes.
•Antimicrobial peptides
Cellular Components:
•Neutrophils(polymorphonuclear: PMN), Mononuclear phagocytes(include monocytes in circulation, histiocytes in
tissues, microglilal cells in the brain, Kupffer cells in the liver and macrophages in serous cavities and lymphoid
organs), dendricitc cells.
•NK cellsare important in defense against viral infections and malignancies.
•Gamma delta T cells(in epithelia) -no MHC
N. B. All components of the non-specific immune system are modulated by products of the specific
immune system, such as interleukins, interferon-g, antibody, etc.

4. How does the host organism detect the presence of infectious
agents and dispose of them without destroying self tissues?
How non-specific is innate immunity really ?
Adaptive immunity mediated by clonally distributed T & B lymphocytes
Characterized by specificity & memory
Innate immunity has long been thought of as a non-specific immune
response
Characterized by engulfment & digestion of microorganisms by
macrophages & leukocytes
Now seen that innate immunity has considerable specificity
Recognizes self & non-self
Discriminates between pathogens
Innate immune response also shown to be a prerequisite for triggering
acquired/adaptive immunity

5. •All multicellular organisms are able to recognize and eliminate
pathogens
•Despite their extreme heterogeneity, pathogens share highly
conserved molecules, called “pathogen-associated molecular
patterns” (PAMPs)
•Host cells do not share PAMPs with pathogens
•PAMPs are recognized by innate immune recognition receptors
called pattern-recognition molecules/receptors (PRMs/PRRs)
Innate Immune Recognition
via Patterns

6. Pathogen-associated molecular patterns
CHALLENGE:How can the host discriminate large numbers of diverse
pathogens from each other &/or from self using a restricted number of
receptors?
SOLUTION: Evolve variety of receptors that recognize conserved motifs
on pathogens that are not found on higher eukaryotes
Pathogen-associated molecular patterns (PAMPs) recognized by pattern
recognition receptors (PRRs) or molecules (PRMs)
Two categories of PRRs:
Those that mediate capture, uptake & presentation of antigen
(scavenger receptors)
Those that lead to the activation of pro-inflammatory pathways
(Toll-like receptors)
PRMs are soluble, secreted proteins, such as SP-A, SP-D, MBL, Ficolins,
CRP.

7. Scavenger receptors
Recently, a series of genes identified in DCs &
macrophages encoding lectin or lectin-like receptors
Preferentially bind to carbohydrate-bearing pathogen-
derived antigens
Multifunctional:
Associated with antigen-uptake –“scavenger receptors”
Important for DC migration (role of chemokine gradient)
Play a role in DC interaction with lymphocytes

8. Functions of membrane bound lectins
produced by dendritic cells and
Langerhans cells:
-MMR, DEC-205 (CD205), and Dectin-2:
Antigen Uptake, DC trafficking.
-Dectin-1 and DC-SIGN (CD209):
T-cell interaction, DC trafficking.
! C-type lectin receptors also recognize
glycosylated virus envelope proteins but
some viruses appear to utilize these
as attachment (& entry?) receptors.

9. FIG. 3. EM of N. meningitidisuptake. WT and SR-A-/-BMM were incubated for various times with 150 live MC58 bacteria per cell at 37°C.
At various intervals, the cells were washed to remove extracellular bacteria before being processed and analyzed by EM.
The fields chosen are representative of the whole M population
Peiser Infect Immun.2002;
70 (10): 5346–5354

10. TLRs are transmembrane proteins
“Toll” identified as essential molecule for embryonic patterning in Drosphila
Evolutionary conserved among insects & humans
Mammalian TLRs have homology to IL-1 receptor in cytoplasmic domain (the Toll-IL1-
R or TIR domain)
Extracellular domain quite different
10 TLRs reported (1-10)
Expressed differentially on immune cells (low level)
Also expressed on other cell types (e.g., endothelial cells)
Respond to different stimuli
Expression modulated in response to stimuli –i.e., inducible
Toll-like receptors

11. TLR1 triacyllipopeptides
TLR2 Bact. Lipoproteins,
LTA, Peptidoglycan
TLR3 dsRNA (viral)
TLR4 LPS
TLR5 Flagellin
TLR6 diacyllipopeptides
TLR7 Natural ligand unknown
TLR8Natural ligand unknown
TLR9 Unmethylated CpG DNA
TLR10?

12. Activation of signal transduction pathways by TLRs induces genes that function in
host defense
Pro-inflammatory cytokines
Chemokines
MHC & costimulatory molecules
iNOS & antimicrobial peptides that directly destroy pathogens
TLRs have “shared” & “specific” signal transduction pathways
Shared –all TLRs & IL1R
4 essential components –adaptor proteins MyD88, TOLLIP & TRAF6, & protein kinase
IRAK
Specific –some, but not all TLRs…
TLR signaling pathways

14. Involvement of TLR in Linking Innate Immunity
to Adaptive Immunity
Nature Immunology 2001 2:675

15. Phagocytosis and immune
recognition of M.
tuberculosis.
Van Crevel, Clin Microb. Rev 15,
294-309, 2002
Tailleux et al., J Exp Med. 2003;197(1):121-7. : „DC-SIGN is the major Mycobacterium tuberculosis receptor on human dendritic cells“.
Complement receptor (CR)3 and mannose receptor (MR), which are the main M. tuberculosis receptors on macrophages, appeared
to play a minor role, if any, in mycobacterial binding to DCs.
The mycobacteria-specific lipoglycan lipoarabinomannan (LAM) was identified as a key ligand of DC-SIGN.

16. -Scavenger receptors are important for antigen uptake,
trafficking, and T cell stimulation.
-Toll-like receptors are a multigene family that initiate pro-
inflammatory gene induction in response to bacterial
products and viral products. Binding of ligands to homo-
or heterodimerised TLRs activates a sequential signalling
cascade involving accessory molecules.
-As presented here, pattern recognition
receptors/molecules support the so-called „stranger
hypothesis“ (Janeway 1989). However, recent work
suggests the relevance of a so-called „danger
hypothesis“ according to which cellular stress resulting
from infection alerts the immune system (Matzinger,
Nature 425: 2003).
SUMMARY

17. Recommended reading:
Zhang and Ghosh: Toll-like receptor-mediated NF-kB activation:
a phylogenetically conserved paradigm in innate immunity
J Clin Invest 107, 13-19, 2001

19. Membrane-associated lectins capture pathogens for intracellular destruction,
degradation & antigen loading of MHC molecules
MMR constitutively internalized from cell-surface & recycled
DEC-205 & DC-SIGN internalized upon ligand binding
C-type lectins as DC antigen receptors
C-type lectins in DC trafficking
MMR appears to direct DCs & macrophages to germinal centers of lymph
nodes & spleen during immune response
Binds sLeX on endothelium
DC-SIGN producing DCs tether & roll on endothelium by interaction with
ICAM-2
Regulated by chemokine gradients
Facilitates endothelial transmigration in vitro