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Presented by Mis Karimi
(PhD student of medicine immunology)
Toll-like receptor (TLR) family
B-cell expression of TLRs

TLR expression patterns and their functions in different B-cell subsets

Expression of TLR on B lymphocytes varies depending on the
mammalian species
Toll-like receptors in human B cells

Naïve human B cells do not express significant levels of TLRs unless
they are pre-stimulated through the BCR

human memory B cells constitutively express TRL2, TLR6, TLR7, TLR9
and TLR10.

As in humans, TLRs are expressed differentially in B cell subsets.
Roles of TLR in activation of B cells
TLR SIGNALING IN B-CELL DEVELOPMENT

Activation of TLR signaling in HSCs shifts their
developmental potential towards myeloid cells

TLR signaling in CLPs causes cell differentiation
into DCs

Transitional B cells can differentiate into mature
B cells, plasma cells and IgM memory B cells
upon TLR activation
Cellular targets of TLR stimulation in human B cells

Interestingly, in the human body the local environment seems to
shape the TLR repertoire

Memory B cells are more reactive and more prone to proliferate
and differentiate into plasma blasts upon TLR stimulation

CpG-containing ODN, it is becoming more and more evident that
only a few B-cell subsets respond to TLR9 stimulation with CpG-ODN

Furthermore, CpG-ODN supported productive CSR in naive human B
cells in the presence of recombinant interleukin-10

In a recent report Rita Carsetti’s group characterized transitional
human B cells as the main non-memory B-cell subset responsive to
TLR9 activation

Recently, studies have described human IgM+ CD27+ B cells as the
main target cells for immunostimulatory DNA ODN
Models for Toll-like receptor (TLR) -mediated B-cell
activation.
TLR signaling in B-cell differentiation

Toll-like receptors were proposed to play a role in Bcell differentiation at early stages of B-cell
development

B-cell precursor maturation in vitro is supported by
the early exposure to TLR4 ligands but arrested upon
stimulation of TLR2

contrast, there is strong evidence that TLR
regulate the differentiation of transitional and
mature B cells.

TLR-mediated activation of the transcription
factor NF-kB is believed to be sufficient to
promote the expression of Blimp-1, a transcription
factor crucial for plasma cell and pre-plasma
memory B-cell differentiation.
TLR signaling in B-cell differentiation

Additionally, a recent study suggested a role for TRAF3 in TLR mediated
and antigen-mediated plasma cell differentiation and IgG secretion.

There are no publications available on the persistence
of TLR expression and the role of TLR in plasma cells.
Modulation of antibody production in vivo

TLR engagement in B cells mediates TI and TD antibody responses

Dual BCR and TLR engagement in antigen-specific B cells induces T
cell-independent CSR or primes B cells for T cell-dependent CSR and
SHM
TI and TD antibody responses
Dual BCR and TLR engagement in CSR and SHM
Modulation of CSR in vitro

In murine B cells the TLR4 ligand LPS promotes the CSR of naive B cells to IgG2b
and IgG3, and to IgG1 and IgE when combined with IL-4.

Additionally, in murine B cells, TLR9 stimulation can inhibit LPS + IL-4- mediated
CSR to IgG1 and IgE and promote IgG2a, IgG2b and IgG3 production
Modulation of CSR in vitro

In the human immune system Andrea Cerutti’s group was the first to
find that CSR to IgG is induced when naive B cells are cultured in the
presence of IL-10 and stimulated with CpG-ODN.

CSR to IgG and IgA was observed when human B cells isolated from
tonsils were challenged with TLR3 ligand Poly I : C and BAFF.
Modulation of CSR in vitro

Moreover, the same group reported that T-cell-independent CSR to
IgA2 is most efficient in human B cells treated with the TLR5 ligand
flagellin or TLR9 ligand CpG DNA in the presence of APRIL.
TLR SIGNALING IN AUTOANTIBODY PRODUCTION

Marshak-Rothstein’s group first demonstrated that a synergistic
engagement of BCR and TLR9 signaling could effectively activate
autoreactive B cells in vitro.

Genetic deficiency of TLR7, TLR9 or MyD88 often leads to reduced
production of autoantibody, and increased expression of TLR7 causes
susceptibility to autoimmune diseases.
TLR SIGNALING IN AUTOANTIBODY PRODUCTION

Shlomchick’s group generates a model of SLE, they found that the
autoreactive B cells actually proliferate and undergo somatic hyper
mutation in the so-called ‘extra follicular’ sites, not in GCs.

When used B cell MyD88-deficient mice crossed to a different SLE
mouse model (lyn-/-) and found a strong dependence on B-cell TLR
signaling for autoantibody level and associated pathological
change.
TLR SIGNALING IN ANTIBODY RESPONSE TO
IMMUNIZATION

In cases of antigens containing defined TLR ligands, TLR signaling does
play important roles in many aspects of antibody response.

For proteins conjugated with TLR ligands, which are typical TD type
antigens, the antigen-specific IgM response is also dependent on Bcell TLR signaling to some degree
TLR SIGNALING IN ANTIBODY RESPONSE TO
IMMUNIZATION
Working model of how VLPs induce Bcell TLR signaling
Immunization mice with several soluble protein antigens
with variable levels of immunogenicity mixed or directly
conjugated to a TLR ligand and found that the magnitude
of the IgG responses was comparable between B cell
MyD88-deficient mice and wild-type controls
TLR-induced cytokine secretion in B cell

Murine IL-10 secretion was detected in MZ B cells in response to single
TLR2, TLR4, TLR9 or combined TLR stimulation but was absent in splenic
follicular B cells whereas IL-6 was detectable in both populations.

Among the murine B-cell subpopulations tested, only follicular B cells
synthesized IFN-γ in response to stimulation with TLR9 ligands
combined with TLR2, TLR4 or TLR7 agonists.
TLR-induced cytokine secretion in B cell


Several reports further indicate that murine B cells produce TNF, IL-6,
IL-12, IL-23 and IL-27 in response to TLR engagement.
Human B cells are generally considered poor cytokine producers. Stimulation
with TLR7 and TLR9 ligands results in the secretion of IL-10, IL-6 and IL-8.
Further, IL-1β and IL-2 secretion have been detected in
response to CpG-ODN.
The role of BCR and MYD88 signaling in B cells
during T-dependent immune responses.
Conclusion:
Perspective
•
• Understanding the mechanisms of how innate signaling contributes to humoral
responses will provide a platform for developing applications, including vaccines,
for human diseases
• TLRs are a potential target for therapeutic intervention in autoimmune diseases.
References

1- Bekeredjian-Ding I, Jego G. Toll-like receptors--sentries in the B-cell
response. Immunology. 2009; 128:311–323.

2- Pone EJ, Zan H, Zhang J, Al-Qahtani A, Xu Z, Casali P. Toll-like receptors
and B-cell receptors synergize to induce immunoglobulin class-switch DNA
recombination: relevance to microbial antibody responses. Critical
Reviews™ in Immunology. 2010;30(1).

3- Hua Z, Hou B. TLR signaling in B-cell development and activation. Cellular
& molecular immunology. 2012;10(2):103-6.

4- Meyer-Bahlburg A, Rawlings DJ. B cell autonomous TLR signaling and
autoimmunity. Autoimmunity reviews. 2008;7(4):313-6.

5- Hou B, Saudan P, Ott G, Wheeler ML, Ji M, Kuzmich L et al. Selective
utilization of Toll-like receptor and MyD88 signaling in B cells for
enhancement of the antiviral germinal center response. Immunity 2011; 34:
375–384.

6- Herlands RA, Christensen SR, Sweet RA, Hershberg U, Shlomchik MJ. T cellindependent and toll-like receptor-dependent antigendriven activation of
autoreactive B cells. Immunity 2008; 29: 249–260.

7- He B, Qiao X, Cerutti A. CpG DNA induces IgG class switch DNA
recombination by activating human B cells through an innate pathway that
requires TLR9 and cooperates with IL-10. J Immunol 2004; 173:4479–91.