5.4 Influence of CD40-signaling on phagocytic cells in the lamina propria of the
5.4.1 Mononuclear phagocytes in the lamina propria of DC-LMP1/CD40 an-
Because of the described colitis, we went ahead and characterized the phagocytic cells of the colonic lamina propria. In contrast to the spleen, macrophages of the gut are also positive for CD11c and MHCII. Therefore, a more complex panel of markers is needed to investigate and differentiate macrophages and DCs.
Single cell suspensions of lamina propria were stained for CD11c and MHCII and cells highly positive for those molecules and negative for F4/80 or CD64, both markers for macrophages, were analyzed for expression of CD11b and CD103. Using this panel one can distinguish three DC subsets (Fig. 5.8 A). Of those, the frequency of the two CD103+ subsets is strongly reduced in the DC-LMP1/CD40 animals on the wild-type background (Fig. 5.8 A). The CD103+CD11b− cells are unchanged in numbers, while CD103+CD11b+ are reduced and CD103−CD11b+ showed an increase in cellularity (Fig. 5.8 C).
CD11b
control DC-LMP1/CD40
CD103
control
DC-LMP1/CD40 CD103+
CD11b- CD103+
CD11b+ CD103 -CD11b+
A B
0 103 104
105 38 ± 4 23 ± 3 5 ± 1 2 ± 0.3
23 ± 2.8 72 ±1.8
0 0.5 1.0 1.5
0 0.5 1.0 1.5
0 5 10 15
# [*103] *
0 103 104 105
0 103 104 105
***
Figure 5.8: CD103+CD11b+ DCs are strongly reduced in the lamina propria of DC-LMP1/CD40 animals. A) Representative FACS plots of DCs of the colonic lamina propria from DC-LMP1/CD40 animals under steady state conditions. Cells were gated on CD11c+MHCII+F4/80−. Numbers in FACS plots indicate percentage of DC subsets as mean± SEM (n = 9)B) Cell numbers show pooled results from two experiments (n = 6).
In order to find out if this reduction in CD103+ DCs is a secondary effect of the col-itic inflammation or a direct effect of the transgene expression, we repeated this analysis in animals that have been treated for three weeks with ABX or that were on the Rag−/−
-5.4 Influence of CD40-signaling on phagocytic cells in the lamina propria of the colon 48 background and therefore lacked inflammation. In both groups we found a decreased fre-quency of CD11b−CD103+ and CD11b+CD103+ populations (Fig. 5.9 A). Also the absolute numbers of CD103+ DCs were strongly reduced in DC-LMP1/CD40 animals on the Rag−/−
background and this tendency was also observed for CD11b+CD103+DC in DC-LMP1/CD40 animals treated with ABX, although it did not reach statistical significance (Fig. 5.9 B). The number of CD103− DCs was also increased in animals treated with ABX but to a much lesser degree than in untreated animals. In animals on the Rag−/−-background we did not find an increase in CD103− DCs.
Macrophages of the gut play an essential role in the homeostasis of the gut and at the same time might express the LMP1/CD40 transgene due to some CD11c expression [103].
To further characterize if macrophages are changed in the transgenic animals, we used a panel of markers developed in the lab of Bernard Malissen [38], allowing to differentiate distinct developmental stages of Ly6Cℎ𝑖monocytes from the moment they leave the circulation (population P1 in Fig. 5.10 A) and enter the tissue until they finally become anti-inflammatory macrophages (population P3/P4 in Fig. 5.10 A). Using this marker-set we could show that
0 103 104 105
0 103 104 105
0 103 104 105
29 ± 1.4 12 ± 1.3 11 ± 1.3
36 ± 4.6 41 ± 5.9
CD11b
ABX treated
control DC-LMP1/CD40
CD103Rag-/-
CD103Rag-/-control
DC-LMP1/CD40 CD103+
CD11b- CD103+
CD11b+ CD103 -CD11b+
A B
2 ± 0.2
0 2 4 6 8 10
0 1 2 3 4 5
0 5 10 15 20
# [*103] *** ***
0 103 104 105
0 1 2 3 4
0 0.5 1.0 1.5
0 5 10 15
# [*103] *
25 ± 1.4 10 ± 1.8 11 ± 0.8 2 ± 0.3
23 ± 1.7 33 ± 4.0
Figure 5.9: CD103+ DC reduction is independent of inflammation in DC-LMP1/CD40 animals. A) Representative FACS plots of DCs of the colonic lamina propria from DC-LMP1/CD40 animals on the Rag−/− background or after ABX-treatment. Cells were gated on CD11c+MHCII+F4/80−. Numbers in FACS plots indicate percentage of DC subsets as mean±SEM from one of two independent experiments (n = 3). B) Representative cell numbers of one of two experiments.
5.4 Influence of CD40-signaling on phagocytic cells in the lamina propria of the colon 49 in DC-LMP1/CD40 animals the percentage of cells in the "waterfall"-gate that fall into the P3/P4 gate was significantly reduced compared to the wild-type controls. The overall cell number on the other hand was strongly increased in all three subsets differentiated here. This is due to the strong inflammation observed in DC-LMP1/CD40 animals which leads to an overall increase in cellularity of the colon. To investigate the influence of the inflammatory milieu we analyzed macrophages in ABX-treated animals as well as in Rag−/−-mice. After ABX treatment we found the distribution of the three subsets unchanged as compared to the wild type. In contrast, we also saw a reduction in P3/P4 in DC-LMP1/CD40 animals on the Rag−/−-background. Taken together, this indicated that changes in macrophages observed in untreated animals are due to the inflammatory milieu and not caused by the transgene expression.
Ctr DC-LMP1/CD40 Ctr
DC-LMP1/CD40
MHCII
Ly6C
P1 P2 P3/P4
% of waterfall cells
ABX treated
0 102 103 104 105
untreated
% of waterfall cells 0
10 20 30 40
0 20 40 60
0 103 104 105
0 102 103 104 105
0 103 104 105
Rag-/-
Rag-/-A
B
0 102 103 104 105
0 102 103 104 105
0 102 103 104 105
0 102 103 104 105
Aqua L/DCD45 1cCD1CD11b
0 103 104 105
0 102 103 104 105
Ly6C CD64
0 102 103 104 105
0 103 104 105
MHCII
Ly6C
0 10 20 30 40 50 * 0
10 20 30 40
0 20 40 60
0 10 20
** 30 ***
P3/P4
P1 P2
waterfall
0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4
0 0.2 0.4 0.6 0.8
0 0.2 0.4 0.6 0.8
0 0.5 1.0 1.5
0 0.5 1.0 1.5
*** ***
**
** **
*
0 102 103 104 105
0 10 20 30 40
0 20 40 60
0 20 40 60
% of waterfall cells 0
0.2 0.4 0.6 0.8
0 0.2 0.4 0.6 0.8 1.0
0 0.5 1.0 1.5
# [*105]# [*105]# [*105]
P1 P2 P3/P4
Figure 5.10: Development of macrophages in DC-LMP1/CD40 animals. A) Gat-ing strategy to analyze the development from Ly6Cℎ𝑖 monocytes towards tissue-resident macrophages. B) Distribution of cells inside the "waterfall"-gate into the gates P1, P2 and P3/P4 in untreated C57BL/6, ABX treated C57BL/6 and Rag−/−-animals (n = 3)
The absolute number of macrophages on the other hand was strongly reduced in both
5.4 Influence of CD40-signaling on phagocytic cells in the lamina propria of the colon 50 groups and in all subsets analyzed, although it did not reach statistical significance after ABX treatment. This finding implicates that the reduction in the relative amount of P3/P4 might be dependent on a bacterial signal in addition to the CD40 stimulus and also hints at a possible dependence of macrophages in the lamina propria on cells of the adaptive immune system and commensal bacteria to properly differentiate.
Since we found a strong reduction of CD103+ DCs in the lamina propria of the colon and these cells are known to migrate towards the draining lymph node, we analyzed DCs in the mesenteric lymph node for the presence of the four DC subsets that can be differentiated in this organ by CD103 and CD11b. We found a small reduction of the percentage of DCs inside the live cell gate but this was compensated for by a larger number of living cells, so that the final number of DCs per mLN was the same (Fig. 5.11 A). Again this was independent of the proinflammatory milieu since we found the same in animals that were treated with ABX.
B A
0 1 2 3 4
# of DCs [*105]# of DCs [*105]
0 0.5 1.0 1.5 2.0
0 102 103 104 105
control DC-LMP1/CD40
CD11c
MHCII 0 102 103 104 1050
102 103 104 105
0 102 103 104 105
ABX treateduntreated 1.1 ± 0.2 0.5 ± 0.1
0.5 ± 0 0.7 ± 0
0 102 103 104 105
0 103 104 105
0 102 103 104 105
0 103 104 105
CD11b
CD103
26 ± 2 15 ± 1.3
52 ± 3.2
8 ± 1 3 ± 0.2
85 ± 1.3 27 ± 1.3 20 ± 0.4
46 ± 2
13 ± 0.8 3 ± 0.4
79 ± 0.6
control DC-LMP1/CD40
ABX treateduntreated
CtrDC-LMP1/CD40 CD103+
CD11b- CD103+ CD11b+ CD103
-# [*104]# [*104]
0 2 4 6 8
0 1 2 3 4
0 20 40 60
0 1 2 3 4 5
0 1 2 3 4
0 5 10 15
* **
*** ***
Figure 5.11: CD103+DCs are strongly reduced in mLN of DC-LMP1/CD40 animals.
A) Representative FACS plots of DC gate in mLN of control and DC-LMP1/CD40 animals with and without ABX treatment and the statistics for these CD11c+MHCII+ cells. B) DCs from A were analyzed using CD103 and CD11b. Number in representative FACS plots are mean ± SEM (statistics for n = 10 untreated animals and n = 5 ABX treated ones).
Next we analyzed the DC subsets that can be found in the mLN and could indeed confirm the results of the lamina propria. The CD103+CD11b− subset was reduced by about 60 % when looked at the relative amount and 50 % when absolute cell numbers were considered (Fig. 5.11 B). This reduction was even stronger in the CD103+CD11b+ compartment. Here we found reductions between 70 and 80 %.
5.4 Influence of CD40-signaling on phagocytic cells in the lamina propria of the colon 51 All these results were again independent of an inflammation, since we found the same in animals treated with ABX. Because we found the same numbers of DCs, defined as CD11c+MHCII+ cells, but a reduction in both CD103+ populations, it is also to be ex-pected that an increase of another subset would be detected. Indeed, this was the case for the CD103− compartment, although it did not reach statistical significance.
Using the transgenic model, we were unable to differentiate if this reduction is due to migration or cell death or both. To address this we made again use of the anti-CD40 injection system.