In our study, we tried to find out the mechanism of age-related immune response
against HBV by using HBV-transfected C3H/HeN mouse model because of the
age-dependent HBV clearance of C3H/HeN mice. KC is a specialized tissue resident
macrophage that contributes to liver tolerance which has the ability to decrease the
inflammation causing by foreign antigen from portal vein or hepatic artery. In our
previous studies, we found that the dynamically changed composition of gut microbiota
was correlated with the age of C3H/HeN mice and the age-related HBV clearance in
C3H/HeN mice. We further supposed that gut microbiota which was suggested to shape
liver immunity in many references might involve in the process of immune response
against HBV. Based on these, we speculated whether the interaction between KCs and
gut microbiota could influence the outcome of HBV transfection in C3H/HeN mice.
However, to investigate innate immunity about HBV in our mouse model, there are
many disturbances caused by hydrodynamic injection. For this reason, we must examine
our data carefully and rule out the artificial factors.
It’s difficult and complicated to confirm the role of KCs in the process of immune
response during the HBV exposure. To begin with, we indicate that KCs may cause the
immune-tolerant effect in young C3H/HeN mice during the exposure of HBV in the
KCs depletion experiment. But the depletion of KCs could mere be a therapeutic
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treatment that indirectly compensate the immune-tolerant pathway from HBV but not
directly disrupt it. We didn’t know how KCs involved in HBV clearance in adult
C3H/HeN mice. Therefore, we tried to investigate whether the population of liver
macrophages changed after the exposure of HBV. We supposed that HBV couldn’t
induce notable immune response in young C3H/HeN mice because of the HBV
tolerance. The dynamic change of liver macrophage populations can be referred to the
effect of hydrodynamic injection. The results of control groups also support this
concept. Compared with the young C3H/HeN mice, the adult C3H/HeN and young
C3H/HeJ mice can be induced the reduction of KCs especially 2 days after HBV
transfection. These results correspond with the experiment of KC depletion. We
consider the reduction of KCs is an immune activated process that led to the clearance
of HBV by adaptive immunity ultimately. The next question is how does HBV induce
the reduction of KCs. It can be through direct or indirect contact between KC and HBV.
To further investigate the correlation between KC and HBV, the mutant HBV can be
applied. For instance, the core-null HBV or HBCY132A mutant HBV which are known
for the high HBV-persistent rate in mouse model. The intact core antigen may be a
candidate that induces KCs reduction. We also need to further investigate whether there
is any difference which may cause distinguishable fates of KCs between the steady-state
KCs in HBV clearable group and HBV tolerant group.
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In our previous study, after antibiotic treatment, about 50% of adult C3H/HeN
mice became tolerance to HBV. We investigated the populations of liver macrophages
from ABX treated mice and found the significant reduction of KCs at day 3 after HBV transfection compared to other group that didn’t receive ABX treatment. This result
indicates that the restoration of KCs at day 3 after HBV transfection may be an
important step to HBV clearance. KCs that differentiate from infiltrating macrophages
can transiently express inflammatory cytokines before becoming to M2-like
macrophages (Bleriot et al., 2015). The function of KC at this vague stage of
differentiation is unclear. To confirm this question, we can investigate the population of
KCs in the experiment of KC depletion. The restoration of KCs at day 3 after HBV
transfection should be observed if it is important for HBV clearance.
In young C3H/HeJ mice, we found that TLR4 signaling was important for HBV
persistence. This result may support our hypothesis that we assumed some foreign
antigens, such as LPS, primed KCs into immune-tolerant phenotype that caused HBV
tolerance and some antigens promoted immune activation against HBV. The TLR4
signaling may be the immune-tolerant and dominative signal that results in immune
tolerance to HBV in young C3H/HeN mice. In adult C3H/HeN mice, we suppose KC
still contributes immune-tolerant effect because of its important role in liver tolerance
but the immune-tolerant effect of KC can be disrupted during exposure to HBV. As our
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previous study, the composition of gut microbiota in C3H/HeN mice dynamically
changed with age and became stable at 12 weeks old. Liver receives signals trigger by
foreign antigen derived from gut microbiota can also change with age. We suppose that
the composition of gut microbiota in adult C3H/HeN mice can provide liver immune
environment with the ability to suppress the immune-tolerant effect of KC during
exposure to HBV. The reduction of KCs can be one of the pathway to suppress the
immune-tolerant effect. In view of this concept, TLR4 may be the rescue signal for KCs
and can be verified by treating LPS before HBV transfection on adult C3H/HeN mice.
If treating LPS on adult C3H/HeN mice can rescue KCs, the immune response against
HBV may will be changed. However, there is still an important point that we should
consider. The loss of TLR4 signaling can be an immune-activated process that
strengthen the innate immune response and make the liver immunity trend to clear
pathogen, such as HBV.
In our study, we found an age-dependent response of KCs reduction in C3H/HeN
mice after HBV transfection. We have not further investigated the correlation between
this age-dependent fates of KCs and the composition of gut microbiota. To find out
whether gut microbiota that involve in HBV clearance in our C3H/HeN mice model
participate in the age-dependent reduction of KCs, we need to investigate the population
of KCs in germ-free environment. It can be mere an age-dependent phenomena, if the
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result of age-dependent reduction of KCs can be reproduced in germ-free C3H/HeN
mice. We also need to confirm whether our study is strand specific since our study all
based on C3H/HeN mice.
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