ISSN 0006-2979, Biochemistry (Moscow), 2024, Vol. 89, No. 5, pp. 904-911 © Pleiades Publishing, Ltd., 2024.
904
Microglia and Dendritic Cells as a Source of IL-6
in a Mouse Model of Multiple Sclerosis
Violetta S. Gogoleva
1,a
*, Quynh Chi Nguyen
2
, and Marina S. Drutskaya
1
1
Center for Precision Genome Editing and Genetic Technologies for Biomedicine,
Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 117997 Moscow, Russia
2
Faculty of Biology, Lomonosov Moscow State University, 119991 Moscow, Russia
a
e-mail: violettegogoleva@mail.ru
Received December 6, 2023
Revised February 1, 2024
Accepted February 6, 2024
Abstract— Multiple sclerosis (MS) is a complex autoimmune disease of central nervous system (CNS) character-
ized by the myelin sheath destruction and compromised nerve signal transmission. Understanding molecular
mechanisms driving MS development is critical due to its early onset, chronic course, and therapeutic approaches
based only on symptomatic treatment. Cytokines are known to play a pivotal role in the MS pathogenesis with
interleukin-6 (IL-6) being one of the key mediators. This study investigates contribution of IL-6 produced by mi-
croglia and dendritic cells to the development of experimental autoimmune encephalomyelitis (EAE), a widely
used mouse model of MS. Mice with conditional inactivation of IL-6 in the CX
3
CR1
+
cells, including microglia, or
CD11c
+
dendritic cells, displayed less severe symptoms as compared to their wild-type counterparts. Mice with
microglial IL-6 deletion exhibited an elevated proportion of regulatory T cells and reduced percentage of patho-
genic IFNγ-producing CD4
+
T cells, accompanied by the decrease in pro-inflammatory monocytes in the CNS at
the peak of EAE. At the same time, deletion of IL-6 from microglia resulted in the increase of CCR6
+
T cells and
GM-CSF-producing T cells. Conversely, mice with IL-6 deficiency in the dendritic cells showed not only the previ-
ously described increase in the proportion of regulatory T cells and decrease in the proportion of T
H
17 cells, but
also reduction in the production of GM-CSF and IFNγ in the secondary lymphoid organs. In summary, IL-6 func-
tions during EAE depend on both the source and localization of immune response: the microglial IL-6 exerts both
pathogenic and protective functions specifically in the CNS, whereas the dendritic cell-derived IL-6, in addition to
being critically involved in the balance of regulatory T cells and T
H
17 cells, may stimulate production of cytokines
associated with pathogenic functions of T cells.
DOI: 10.1134/S0006297924050109
Keywords: interleukin-6, microglia, dendritic cells, experimental autoimmune encephalomyelitis, multiple
sclerosis, mouse models
Abbreviations: ΔDC, gene deletion only in dendritic cells; ΔMG, gene deletion only in microglia; BBB,blood-brain barrier;
CNS, central nervous system; EAE, experimental autoimmune encephalomyelitis; IL, interleukin; MS, multiple sclerosis;
T
H
,Thelper cells; T
reg
,regulatory T cells.
* To whom correspondence should be addressed.
INTRODUCTION
Multiple sclerosis (MS) is a chronic autoimmune
disease that affects the central nervous system (CNS)
and causes severe consequences, including visual dis-
turbances, motor and cognitive impairments. In recent
years, there has been an increasing trend in the
number of people diagnosed with MS, however, only
symptomatic treatments aimed at modulating the
symptoms are currently available [1]. Therefore, the
search for new therapeutic targets remains a very
important task. One of the most widely used experi-
mental models of MS in mice is experimental autoim-
mune encephalomyelitis (EAE) [2]. Pathogenesis of
IL-6 FROM MYELOID CELLS IN EAE 905
BIOCHEMISTRY (Moscow) Vol. 89 No. 5 2024
EAE primarily involves the activation of CD4
+
T cells,
followed by their differentiation, and infiltration into
the CNS in response to immunization with antigens
from the myelin sheath of neurons in complete Fre-
und’s adjuvant [3]. Cytokines, including IL-6, play a
crucial role in EAE pathogenesis. In particular, it has
been shown that pharmacological and genetic inacti-
vation of IL-6 in the mouse model of multiple sclerosis
leads to a reduction in disease severity [4] or absolute
resistance [5].
It has been established that the pathogenic role
of IL-6 is realized via various mechanisms involved in
the regulation of blood-brain barrier (BBB) permea-
bility and the development of CD4
+
T cell subsets. Im-
munization of wild-type mice with the myelin peptide
MOG
35-55
was shown to increase the expression of ad-
hesion molecules such as VCAM-1 and ICAM-1 on the
surface of endothelial cells in the BBB as compared to
IL-6-deficient mice [5]. It is known that activation of
two subunits of the IL-6 receptor complex, IL-6Rα and
gp130, is required for IL-6 signal transduction. It has
been shown that trans-presentation of IL-6 (trans-
duction of an intracellular signal by interaction of
IL-6R–IL-6 on the surface of one cell with gp130 on the
surface of another) is necessary for the polarization
of pathogenic T helper cells producing IL-17A (T
H
17
cells) in the EAE model [6]. This has been confirmed
by the fact that deletion of gp130 from the surface of
T cells suppresses the differentiation of CD4
+
T cells
into FoxP3
+
regulatory T cells (T
reg
), thus facilitating
the development of RORγt
+
T
H
17 cells [7]. Remarkably,
there is a positive feedback between IL-6 and IL-17A
produced by pathogenic T
H
17 cells: IL-17A stimulates
IL-6 production by astrocytes, which further facilitates
T
H
17 polarization [8,9].
The main sources of IL-6 in the CNS are various
cells of non-immune origin, in particular, neurons,
astrocytes, and endothelial cells [10], but in the EAE
model the main source of IL-6 are myeloid cells [6],
including dendritic cells and microglia (resident mac-
rophages of the CNS), in particular. Although there is a
large amount of data supporting various functions of
IL-6 in the EAE model, the characteristics of cytokine
production by T cells over the course of disease patho-
genesis with respect to the specific subpopulations of
myeloid cells have not been investigated in sufficient
detail, which was the aim of this study.
MATERIALS AND METHODS
Mice. Cd11c
Cre
× Il6
fl/fl
(mice with Il6 deletion pre-
dominantly in dendritic cells) [11] and Cx3cr1
CreER
× Il6
fl/fl
(mice with Il6 deletion in CX
3
CR1
+
myeloid cells, includ-
ing microglia). Il6
fl/fl
mice [12] were crossed to Cx3cr1
CreER
mice [13] to generate mice with Il6 deletion in CX
3
CR1
+
myeloid cells. Both male and female mice aged 9 to 12
weeks were used. Mice were bred and housed in SPF
conditions at the Animal Facility of the Institute of Cy-
tology and Genetics, Siberian Branch of the Russian
Academy of Sciences and at the Animal Facility of the
Center for Precision Editing and Genetic Technologies
for Biomedicine, Engelhardt Institute of Molecular Bi-
ology, Russian Academy of Sciences [EIMB RAS] (un-
der the contract #075-15-2019-1660 from the Ministry
of Science and Higher Education of the Russian Fed-
eration). All manipulations with animals were carried
out in accordance with the protocol approved by the
Bioethics Committee of the EIMB RAS (Protocol No. 3
from 21/09/2023).
Tamoxifen treatment. Tamoxifen (Sigma Aldrich,
USA) was dissolved in corn oil (Sigma Aldrich) to a
concentration of 15 mg/ml by prolonged incubation
with continuous shaking on a thermoshaker at 37°C
overnight and protected from light. Two ml aliquots
of the obtained solution were placed into tubes and
stored at 4°C for 5days. To induce IL-6 deletion in mi-
croglia, 8-9-week-old Cx3cr1
CreER
×Il6
fl/fl
mice and con-
trol Il6
fl/fl
mice were injected intraperitoneally daily
with 100 µl of tamoxifen solution at a dose of 75 mg/kg
for 5 days.
EAE induction. Mice were subcutaneously im-
munized with 100 µg of MOG
35-55
-peptide (myelin oli-
godendrocyte glycoprotein; Anaspec, USA) in complete
Freund’s adjuvant (Sigma Aldrich) supplemented with
5 mg/ml of inactivated Mycobacterium tuberculosis
(Difco, USA), followed by intraperitoneal injections of
200 ng Pertussis toxin (Sigma Aldrich) on days 0 and
2 to increase BBB permeability. EAE clinical scores
were defined as follows: 0 – no disease; 0.5 – partial
tail paralysis; 1– complete tail paralysis; 1.5– partially
impaired righting reflex; 2– impaired righting reflex;
3–hind limbs paresis; 3.5– complete paralysis of hind
limbs; 4 – forelimbs paresis; 4.5 – complete paralysis
of forelimbs.
Cell isolation. For isolation of blood mononu-
clear cells, peripheral blood was collected in tubes
with heparin and centrifuged (without acceleration
or brakes) in a Ficoll density gradient for 30 min
(1.077 g/cm
3
, PanEko, Russia). Single cell suspensions
of spleen and lymph nodes were prepared by mechan-
ical dissociation through 70 µm filter (NEST, China) in
PBS supplemented with 2% FBS. Red blood cells were
lysed in ACK buffer (1.5 M NH
4
Cl; 100 mM KHCO
3
;
10 mM EDTA-2Na in distilled water, pH 7.2). Immune
cells from the CNS were isolated according to the pro-
tocol [14]. Briefly, mice were anesthetized and tran-
scardially perfused using 0.9% NaCl solution. Spinal
cord and brain were removed, mechanically dissoci-
ated, and digested enzymatically in DPBS containing
1.5 mg/ml collagenase II (Gibco) and 50 µg/ml DNAse I
(Roche, Switzerland). Cells were homogenized using
GOGOLEVA et al.906
BIOCHEMISTRY (Moscow) Vol. 89 No. 5 2024
the syringe with 18G × 1.5′′ needle and washed in PBS
supplemented with 2% FBS. Next, fractions of immune
cells were separated by centrifugation (500g, 25°C,
40 min, (without acceleration or brakes) in a Percoll
density gradient (30/37/70, GE Healthcare, USA).
Flow cytometry analysis. For intracellular cyto-
kine staining, single cell suspensions prepared from
spleen or lymph nodes were stimulated with phor-
bol-12-myristate-13-acetate (PMA; Sigma Aldrich),
500 ng/ml of ionomycin (Sigma Aldrich) for 4 h, 37°C,
5% CO
2
in the presence of 3 mg/ml of Brefeldin A
(eBioscience, USA). To prevent non-specific binding
of antibodies, single cell suspensions were incubated
for 20 min at 4°C with purified anti-mouse CD16/CD32
(clone 2.4G2, in-house DRFZ collection), washed and
stained with following antibodies: anti-CD45 (clone30-
F11, BioLegend, USA), anti-CD11b (cloneM1/70, BioLeg-
end), anti-Ly6C (clone HK1.4, Invitrogen, USA), anti-
MHCII (clone M5/114.15.2, BioLegend), anti-CX
3
CR1
(clone SA011F11, BioLegend), anti-CD4 (clone RM4-5,
BioLegend), anti-TCRb (clone H57-597, eBioscience),
anti-IFNγ (clone XMG1.2, Biolegend), anti-IL-17A
(cloneeBio17B7, BioLegend), anti-GM-CSF (cloneMP1-
22E9, BioLegend), anti-FoxP3 (clone FJK-16s, Invitro-
gen), anti-RORγt (clone B2D, Invitrogen). Dead cell
exclusion was performed by using a Fixable Viabil-
ity Dye (eBioscience). Samples were acquired with
BD FACSCanto II or BDFACSAria III (Beckton Dick-
inson, USA). CD45
+
CD4
–
CX
3
CR1
+
blood monocytes or
CD45
+
CD11b
+
CX
3
CR1
+
microglia were sorted using a
BDFACSAriaIII with a purity of >90%. Data were ana-
lyzed using FlowJo Software (Beckton Dickinson).
ELISA. Sorted monocytes and microglia were
activated with lipopolysaccharide (LPS form E. coli
O111:B4, Sigma [100 ng/ml] for 4 h). IL-6 concentra-
tion in supernatant was determined using mouse IL-6
ELISA Ready-SET-Go! kit (eBioscience) according to
manufacturer’s instructions.
Statistical analysis. Statistical analysis was per-
formed using GraphPad Prism 9. All the data were
analyzed using unpaired Student’s t-test or one-way
ANOVA. Differences were considered significant when
p-values were<0.05.
RESULTS AND DISCUSSION
Myeloid cell-derived IL-6 plays a critical role in
the pathogenesis of EAE. To investigate role of IL-6
produced by myeloid cells in EAE development mice
with IL-6 deletion either (i) only in dendritic cells
(Il6
ΔDC
), or (ii) only in microglia (Il6
ΔMG
) were used.
Littermate Il6
fl/fl
were used as control mice in all ex-
periments. Mice with IL-6 deletion in dendritic cells
have been previously generated and are character-
ized by constitutive inactivation of IL-6 in the CD11c
+
cells [11,15]. Mice with IL-6 deletion in microglia were
generated by crossing Cx3cr1
CreER
mice, which express
tamoxifen-dependent Cre-recombinase under the con-
trol of the CX
3
CR1 promoter [13], to mice with the
floxed Il6 gene (Il6
fl/fl
) [12]. The principle of this system
is the cell-specific inactivation of the Il6 gene flanked
by loxP-sites (floxed) by Cre-recombinase fused with
the mutant form of the estrogen receptor only in the
CX
3
CR1
+
cells in response to the administration of
tamoxifen (Fig.1a).
For tissue-specific inactivation of IL-6 exclusive-
ly in microglia, Cx3cr1
CreER
×Il6
fl/fl
and wild type mice
(Il6
fl/fl
) were injected with tamoxifen at a dose of
75µg/g for 5 days; 14days after tamoxifen administra-
tion, IL-6 deletion occurred both in monocytes (Fig.1b)
and dendritic cells, as well as in microglia [13]. After
complete repopulation of CX
3
CR1
+
myeloid cells from
the bone marrow, i.e., 28 days after tamoxifen admin-
istration, mice retained IL-6 deletion only in the pop-
ulation of long-lived tissue-resident macrophages, in-
cluding microglia (Fig.1c).
EAE was induced by immunization with the
MOG
35-55
-peptide in complete Freund’s adjuvant, fol-
lowed by injection of Pertussis toxin to increase BBB
permeability. Clinical signs were assessed starting day
8 after immunization. Mice with IL-6 deficiency only
in microglia or only in dendritic cells developed mild-
er disease symptoms as compared to wild-type mice
(Fig. 1d). These results are consistent with previous
observations indicating that exactly dendritic cells [6]
and microglia [16] are critical sources of IL-6 in the
EAE model.
Microglia-derived IL-6 regulates immune re-
sponse in the CNS at the peak of EAE. Given that mi-
croglia are tissue-resident macrophages in the CNS, it
was hypothesized that the functions mediated by these
cells would mainly affect the immune response in the
CNS. Therefore, on day 16 after immunization (effector
phase of the disease), the frequency of myeloid cells
and antigen-specific CD4
+
T cells in the CNS was as-
sessed by flow cytometry. Mice with IL-6 inactivation
in microglia showed a reduced frequency (Fig.2a) and
absolute number (Fig.2b) of Ly6C
hi
MHCII
+
monocytes,
which play an exclusively pathogenic role in EAE.
Additionally, there was a decrease in the percentage
of IFNγ-producing CD4
+
T cells (Fig. 2c). These results
are consistent with each other, as it is precisely IFNγ
that supports differentiation of the Ly6C
hi
-monocytes
into MHCII
+
effector dendritic cells [17]. At the same
time, these findings are consistent with the previously
published data on the stimulation of T
reg
development
(Fig.2d) at low concentrations of IFNγ[18].
As shown in the current study, mice with microg-
lial IL-6 deletion develop milder EAE symptoms as
compared to wild-type mice, yet, they do not exhibit
complete resistance to disease development (Fig. 1d).
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BIOCHEMISTRY (Moscow) Vol. 89 No. 5 2024
Fig. 1. Mice with tamoxifen-dependent inactivation of IL-6 in CX
3
CR1
+
microglia are hyposusceptible to EAE induction. a)Scheme
of experiment. Mice were administered Tamoxifen (75µg/g) i.p. for 5 consecutive days. At 7-14 days after Tamoxifen injec-
tions, IL-6 deletion was detected in both tissue-resident macrophages and monocytes, but after 28 days, replenishment of the
monocyte pool from the bone marrow occurred and IL-6 deficiency was observed only in tissue-resident macrophages includ-
ing microglia; b)concentration of IL-6 in the supernatant of sorted CX
3
CR1
+
monocytes isolated from the peripheral blood of
Cx3cr1
CreER
×Il6
fl/fl
mice on days 0, 14, 28after Tamoxifen administration and activated with LPS for 4 h; ND – not detected;
c)concentration of IL-6 in the supernatant of sorted CX
3
CR1
+
microglia isolated from the CNS of Cx3cr1
CreER
×Il6
fl/fl
mice on day
28 after Tamoxifen administration and activated with LPS for 4h; d)Clinical disease course of MOG
35-55
emulsified in complete
Freund’s adjuvant-induced EAE in wild-type mice (Il6
fl/fl
), mice with IL-6 deletion in microglia (Il6
ΔMG
), and mice with IL-6 de-
letion in dendritic cells (Il6
ΔDC
). Data are shown as mean ±SEM and are representative of three independent experiments with
four or more mice per group in each experiment.
Moreover, these mice show an increase in the per-
centage of T
reg
, that suppress the development of EAE
(Fig.2d), suggesting the presence of an additional com-
ponent that contributes to the manifestation of clini-
cal symptoms. We hypothesized that these mice may
demonstrate an increase in the infiltration of patho-
genic T cells into the CNS. The CCR6/CCL20 axis is cru-
cial for the migration of immune cells into the CNS
and is particularly important for the initial wave of
T cell infiltration into the CNS [19]. Indeed, mice with
IL-6 deletion in microglia exhibited an increase in the
frequency of CCR6
+
T cells in the CNS (Fig. 3a). Fur-
thermore, these mice showed an increased percent-
age of GM-CSF-producing, but not IL-17A- producing,
CD4
+
T cells (Fig. 3b). GM-CSF production by T cells is
critically important for the pathogenesis of EAE [20,
21], as GM-CSF promotes the migration of immune
cells into the CNS [22]. Thus, the increased presence of
CCR6
+
Tcells in the CNS correlates with the enhanced
polarization of T cells into GM-CSF-producing cells.
Thus, the reduction in the severity of clinical symp-
toms of EAE in mice with microglial IL-6 inactivation
correlated with a decrease in the percentage and ab-
solute number of inflammatory Ly6C
hi
MHCII
+
mono-
cytes in the CNS, as well as with reduced IFNγ pro-
duction by T cells and an increase in the proportion
GOGOLEVA et al.908
BIOCHEMISTRY (Moscow) Vol. 89 No. 5 2024
Fig. 2. IL-6 produced by microglia stimulates development of pathogenic monocytes and IFNγ production by T cells in the CNS
at the peak of EAE. a)Frequency of Ly6C
hi
MHCII
+
cells among CD45
+
CD11b
+
cells in the CNS at the peak of EAE; b)absolute num-
ber of Ly6C
hi
MHCII
+
cells in the CNS at the peak of EAE; c)frequency of IFNγ-producing cells restimulated with PMA/ionomycin
among CD4
+
TCRβ
+
cells in the CNS at the peak of EAE; d)frequency of FoxP3
+
T
reg
among CD4
+
TCRβ
+
cells in the CNS at the peak of
EAE. Pooled(a,c, andd) or representative(b) data are shown with number of mice for each genotype n=5-6. Data are shown as
mean ±SEM. Student’s t-test or Mann–Whitney test; *p<0.05; **p<0.01.
Fig. 3. IL-6 deletion in microglia results in the increased T cell migration and induction of GM-CSF by CD4
+
T cells in the CNS.
a)Frequency of CCR6
+
cells among CD4
+
TCRβ
+
cells in the CNS at the peak of EAE. b)Frequency of GM-CSF-producing cells re-
stimulated with PMA/ionomycin among CD4
+
TCRβ
+
-cells in the CNS at the peak of EAE. Pooled (a) or representative (b) data are
shown with number of mice for each genotype n=5-6. Data are shown as mean±SEM. Student’s t-test or Mann–Whitney test;
*p<0.05; ***p<0.001; ns,non-significant.
of protective T
reg
cells. At the same time, partial re-
sistance to EAE in mice with IL-6 inactivation in mi-
croglia may be associated with increased of T cell mi-
gration into the CNS, coupled with an increase in the
percentage of the GM-CSF-producing CD4
+
T cells.
IL-6 from dendritic cells not only determines
the T
H
17/T
reg
ratio, but also affects IFNγ and GM-
CSF production in the peripheral lymphoid organs
during EAE. It is known that one of the functions
of IL-6 in EAE is to inhibit of the transcription factor
FoxP3, which, in turn, suppresses development of pro-
tective T
reg
[23]. On the other hand, IL-6 is crucial for
the development of T
H
17 cells [6]. Indeed, a decrease
in the percentage of RORγt
+
T
H
17 cells and an increase
in the percentage of FoxP3
+
T
reg
(Fig. 4a) were observed
in the lymph nodes at the peak of EAE in mice with
IL-6 deletion in dendritic cells. This is consistent with
previous studies on the pathogenic role of IL-6 pro-
duced by dendritic cells.
Next, we addressed cytokine production by T cells
isolated from lymph nodes and spleens of Il6
fl/fl
and
Il6
ΔDC
mice at the peak of EAE and restimulated with
PMA/ionomycin. It was found that IL-6 deletion in den-
dritic cells does not affect the production of IL-17A by
T cells (Fig. 4b), which is consistent with the literature
[6]. However, the Il6
ΔDC
mice were characterized by a
reduction in GM-CSF (Fig. 4c) and IFNγ (Fig. 4d) pro-
duction both in lymph nodes and in spleen.
Thus, mice with IL-6 deletion in dendritic cells
are characterized by an increase in the proportion of
T
reg
and a decrease in IFNγ and GM-CSF production by
Tcells in peripheral lymphoid organs, resulting in the
development of mild EAE symptoms. Moreover, the
results of this study indicate that IL-6 from dendrit-
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BIOCHEMISTRY (Moscow) Vol. 89 No. 5 2024
Fig. 4. IL-6 from dendritic cells stimulates production of cytokines by CD4
+
T cells in the peripheral lymphoid organs at the peak
of EAE. a)Representative dot plots (left) and percentage (right) of RORγt
+
and FoxP3
+
CD4
+
T cells isolated from lymph nodes
of Il6
fl/fl
and Il6
ΔDC
mice at the peak of EAE. b-d)Frequencies of IL-17A-, GM-CSF-, and IFNγ-producing CD4
+
T cells isolated from
the spleen and lymph nodes and restimulated with PMA/ionomycin. Data are shown as mean ±SEM. Student’s t-test or Mann–
Whitney test; *p<0.05; **p<0.01; ns,non-significant.
ic cells may not only be involved in the induction of
pathogenic T
H
17 cells [6], but also stimulate GM-CSF
and IFNγ production by T cells.
CONCLUSIONS
Cytokines play a key role in the pathogenesis
of EAE. IL-6 is one of the few cytokines that is abso-
lutely required for the development of EAE [24, 25].
Although astrocytes being the main source of IL-6 in
the CNS[10], it has been shown that myeloid cells are
the main source of IL-6 in the EAE model [6]. Inter-
estingly, deletion of IL-6 in LysM
+
myeloid cells (mac-
rophages and neutrophils) does not affect the course
of disease [6, 26]. Microglia and dendritic cells are
critically important IL-6 producing populations in the
pathogenesis of EAE [6].
Indeed, the results of this study demonstrate that
IL-6 deletion in microglia leads to the development of
mild EAE symptoms as compared to wild type mice.
It is worth noting that in another study, IL-6 deletion
in microglia resulted in a reduction in the severity of
clinical symptoms of EAE in female but not in male
mice [16], which correlates with the predominance of
MS within the female population. In this study, mice
with IL-6 deletion in microglia showed a reduction in
the number of pro-inflammatory Ly6C
hi
MHCII
+
-mono-
cytes, which play a central role in the demyelination.
This finding is consistent with the literature demon-
strating a decrease in spinal cord demyelination upon
IL-6 deletion in microglia [16]. On the other hand, this
could also indicate one of the degenerative functions
of IL-6 since the same phenotype is observed upon
IL-6 deletion in various sources in the CNS, namely as-
trocytes and neurons [16]. Furthermore, IL-6 deletion
in microglia resulted in a decrease in IFNγ production
by T cells, which, on one hand, explains the reduced
number of Ly6C
hi
MHCII
+
monocytes [17], and, on the
other hand, is consistent with an increase in the per-
centage of protective T
reg
in the CNS[18].
In contrast to the decrease in clinical symptoms
of EAE, mice with IL-6 deletion in microglia exhibited
increased migration of CD4
+
T cells into the CNS and
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BIOCHEMISTRY (Moscow) Vol. 89 No. 5 2024
increased production of GM-CSF. Indeed, another
study demonstrated that the infiltration of T cells does
not change upon IL-6 deletion from various cellular
sources in the CNS [16]. Furthermore, the results ob-
tained provide evidence for the correlation between
the co-expression of CCR6 and GM-CSF in T cells infil-
trating the CNS [27]. Taken together, these data sug-
gest that in the context of neuroinflammation, mi-
croglia may perform both protective and pathogenic
functions.
On the contrary, the results of this study highlight
the exclusively pathogenic role of IL-6 from dendritic
cells [6]. Specifically, IL-6 from dendritic cells is cru-
cial for maintaining the balance between RORγt
+
T
H
17
cells and FoxP3
+
T
reg
. A therapeutic approach target-
ing this signaling pathway by inhibiting STAT3 with a
small molecule has been recently proposed [28] for
immunomodulation of the clinical symptoms in MS pa-
tients. Interestingly, this study also demonstrated that
IL-6 from dendritic cells is essential for stimulating
production of IFNγ and GM-CSF by T cells, although
IL-6 has not traditionally been considered a cytokine
required for stimulation of GM-CSF production [21].
Thus, while IL-6 produced by microglia may have
both pathogenic and protective functions, IL-6 from
dendritic cells appears to play an exclusively patho-
genic role.
Acknowledgments. The authors are grateful to
K. S.-N. Atrekhany, D. M. Potashnikova, A. P. Dygay, and
R. V. Zvartsev for helpful discussions and technical as-
sistance. The authors are thankful to S. A. Nedospasov
for valuable comments and general supervision of the
project. Experiments with cell sorting were support-
ed by the Development Program of the Moscow State
University (complex FACSAria SORP; Beckton Dickin-
son,USA).
Contributions. M.S.D. conceptualized and super-
vised the study; V.S.G. and Q.C.N. performed experi-
ments, discussed results of the experiments, wrote the
original draft of the paper; M.S.D. edited the manuscript.
Funding. This work was supported by the Russian
Science Foundation (grant no.23-24-00389).
Ethics declarations. All experiments with lab-
oratory animals were conducted in accordance with
the local legislation and institutional requirements.
Theauthors of this work declare that they have nocon-
flicts of interest.
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