Adoptive transfer of LPS-treated BMDCs influences the number and
function of pulmonary memory CD4+ T cells in OVA-induced asthmatic mice
It is widely believed that Th1/Th2 ratio imbalances may lead to the
pathogenesis of allergic asthma, in which memory T cells play a crucial
role in the capacity of initiating Th2 response under repeated allergen
challenges21. Memory T cells can be divided into two
distinct subsets, central memory T cells (TCM cells) and
effector memory T cells (TEM cells), according to their
homing characteristics and effector functions22, 23.
In order to assess whether DClps could suppress the Th2 immune recall
response in airways of treated mice, we sought to examine the number and
function of memory CD4+ T cells in lung tissues. We thus established
asthma model mice and treated these mice with diverse DCs, as described
above; however, instead of sacrificing the mice on day 19, we
rechallenged the animals with OVA from days 35-39 (Fig. 4A).
On day 40, mice were sacrificed and lungs were removed to obtain
single-cell suspensions for the isolation of memory CD4+ T cells. We
confirmed that both DC10 and DClps observably decreased the pulmonary
CD4+CD44high memory T cells, whereas the difference in
DCia was negligible compared to the OVA group (Fig. 4B). On the other
hand, we next identified CD4+TCM cells that were
CD62L+CCR7+ double positive and CD4+ TEM cells that were
CD62L-CCR7- double negative by flow cytometry (Fig. 4B). Surprisingly,
we saw no discernible difference in the proportion of
TCM and TEM cells among mice treated
with DClps, DC10 or DCia. To gain insight into this phenomenon, we
assessed whether the adoptive transfer of DClps affected the
proliferation of pulmonary memory CD4+ T cells with an MLR assay. After
MLR, the proliferation activity of pulmonary memory CD4+ T cells was
determined by CFSE. Consistent with the above results, it was readily
apparent the proliferation activity of pulmonary memory CD4+ T cells
isolated from mice in the DC10 and DClps groups was obviously
suppressed, compared with the DCia and OVA groups, especially on day 3
and day 5 (Fig. 5). Meanwhile, we collected the cell supernatant of MLR
to assess IL-4 and IFN-γ secretion by memory CD4+ T cells. We found that
compared with cells in the OVA group, both TEM and
TCM cells exhibited a notable decline in the secretion
of IL-4 in the DClps and DC10 groups (Fig. 6A), whereas no treatment
effect was detectable in the DCia group (Fig. 6B). Interestingly, in the
DClps and DC10 groups, the level of IFN-γ dramatically reduced in only
TEM cells but not in TCM cells (Fig.
6B). Taken together, these data indicate that the adoptive transfer of
DClps may inhibit the allergen recall response by suppressing memory
CD4+ T cells. Moreover, the reduction in memory CD4+ T cells may well
reduce the conversion of Th2 cells, which further results in the
downregulation of Th2 cytokines and improves the Th1/Th2 imbalance in
the immune response.