Published online before print September 15, 2004
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* Departments of Clinical Neurosciences, Applied Immunology, Karolinska Hospital, and
Medicine, Rheumatology Unit, Karolinska Institutet at Karolinska Hospital, Stockholm, Sweden
1 Correspondence: Applied Immunology Unit, CMM L8:04, Karolinska Sjukhuset, S-171 76 Stockholm, Sweden. E-mail: Asa.Andersson{at}cmm.ki.se
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). Different functional activation states can be induced in M during innate immune activation, and it is this differential activation that might be important in susceptibility/resistance to induction or perpetuation of autoimmunity. In this study, we present an extensive, comparative analysis of the activation phenotypes of M derived from autoimmune-susceptible and autoimmune-resistant rat strains to describe a cellular phenotype that defines the disease phenotype. We included investigation of receptor function, intracellular signaling pathways, cytokines, and other soluble mediators released after activation of cells using a panel of stimuli embracing many activation routes. We report that activation of M from the autoimmune-susceptible strain was associated with alternative activation indicated by induction of arginase activity, a lower production of classical proinflammatory mediators, and a high production of interleukin (IL)-23, and M from the autoimmune-resistant strains were associated with a higher production of proinflammatory mediators, a classical activation phenotype, and preferential induction of IL-12. These M phenotypes thus reflect disparate, genetic cellular programs that define autoimmune susceptibility.
Key Words: cytokine • macrophage activation • autoimmunity
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"Resistance" to experimentally induced autoimmunity is a relative term, as increased complexity of the adjuvant used for immunization can profoundly alter the "resistant" status of a rodent strain. Thus, addition of pertussis toxin is required for induction of myelin oligodendrocyte glycoprotein-experimental autoimmune encephalomyelitis (MOG-EAE) in C57BL/6 mice but not in the DBA/1 mouse strain [3 ], and complete Freund’s adjuvant (CFA)-myelin basic protein (MBP)63–88 but not incomplete Freund’s adjuvant (IFA)-MBP63–88 will induce EAE in PVG rats [4 ]. In the latter case, the severity of the induced EAE varies, and so PVG or BN rats are "less susceptible" rather than being "totally resistant" to disease induction, and this should not be confused with the major histocompatibility complex (MHC)-myelin antigen basis of differential susceptibility in a given strain (e.g., DA rats develop EAE when immunized with MOG but not with MBP). One difference between experimental arthritis and experimental encephalomyelitis rat models has been the more "all-or-nothing" susceptibility/resistance phenotypes described in antigen-specific and nonantigen-specific models [5 ], where DA rats are susceptible to collagen-induced arthritis (CIA) and oil-induced arthritis, and PVG and BN rats are resistant.
Although several autoimmune diseases have historically been considered to be T lymphocyte-mediated, pathological conditions, the central role of macrophages (M) in these conditions has received more attention during recent years. M are present in virtually all types of tissue and have important immunological and pathological functions. As effector cells, they are able to kill microorganisms and tumor cells directly, and they also participate in tissue-remodeling processes. Through their ability to secrete various substances, they affect other cell types, and M-derived products [e.g., nitric oxide (NO), tumor necrosis factor (TNF), and metalloproteinase (MMP)9] have been implicated in autoimmune pathological diseases such as atherosclerosis, RA, and MS. Selective depletion of blood-borne M during EAE (a model for MS) [6
, 7
], nonobese diabetic mouse (a model for T1DM) [8
, 9
], and CIA (a model for RA) [10
, 11
] suppresses the clinical symptoms of each of these diseases, demonstrating the importance of infiltrating M as effector cells during pathogenesis. Taken together with the fact that for these experimental autoimmune inflammatory diseases, several effective therapies to date target M functions or M-derived molecules {e.g., anti-TNF [12
], corticosteroids [13
], CNI-1493 [14
], anti-high-mobility group box 1 (HMGB-1) [15
]}, it is clear that M are indeed central mediators of inflammatory diseases.
Innate immune activation of M is mediated through specific activation through a variety of Toll-like receptors (TLRs), and ligation of these different receptors may result in production of different M products. Among these, NO synthase (NOS) and arginase activities can be induced in M [16
]. Arginine is a substrate for both of these enzymes, being hydroxylated to N omega-hydroxy-L-Arg (NOHA), which is further oxidized to citrulline and NO by NOS, or arginase hydrolyses arginine to L-ornithine and urea. NOHA is a competitive inhibitor of arginase, so it follows that a high NOS activity will be associated with low arginase activity [17
]. The preferential activation of NOS is termed "classic" M activation and that of arginase, "alternative" M activation, the activated phenotypes originally being denoted M1 and M2 [18
].
The induction of classically or alternatively activated M has been associated with differential development of T cell responses [19
, 20
]. The T cell cytokines in turn regulate further M activation phenotypes [21
]. In addition to the described NO/arginase circuit, the intriguing balance between the proinflammatory cytokines interleukin (IL)-12 and IL-23 has also been reported to be of importance for determination of induced T cell phenotypes. IL-12 and IL-23 share the p40 subunit that together with p35, forms IL-12, and IL-23 is comprised of p40 and p19. The accessibility of p35 and p19 will thus decide which of these cytokines will dominate the response [22
].
We here report that activation of M from the autoimmune-resistant rat strains was associated with a higher production of proinflammatory mediators and a classical activation phenotype, and M from the autoimmune-susceptible strain were associated with alternative activation indicated by induction of arginase activity. In addition, M from the most autoimmune-susceptible DA strain preferentially expressed p19 (IL-23), and p35 (IL-12) dominated in M derived from the more autoimmune-resistant strains. Taken together, we here reveal several differential factors that might be of importance when defining autoimmune resistance and susceptibility.
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M cell culture and harvesting
Femoral bone marrow (BM) cells were collected by flushing through medium with a 21-gauge needle. Single-cell suspensions were prepared and resuspended in Dulbecco’s modified Eagle’s medium (Gibco-BRL, Grand Island, NY) supplemented with 20% heat-inactivated fetal calf serum, 1 mM sodium pyruvate, 100 U/ml penicillin, 100 µg/ml streptomycin, 2 mM L-glutamine, and ß-mercaptoethanol (all reagents from Life Technologies, Paisley, Scotland) and 20% L929 cell line supernatant (SN). Cells were cultured at a density of 2 x 106cells/ml at 37°C in a humidified incubator for 8 days and for a further 2 days without 20% L929 SN. Cells were detached by adding prewarmed (37°C) Trypsin-EDTA (Life Technologies) and replated at 1 x 105 cells/ml in complete medium without L929 SN in 24-well plates (Nunc, Roskilde, Denmark) or in eight-well chamber slides (Lab Tek, New Zealand).
Antigens
All reagents were obtained from Sigma (Sollentuna, Sweden) unless otherwise stated. Zymosam, latex beads, and Mycobacterium tuberculosis (Difco Labs, Detroit, MI) were individually applied to M cultures at a concentration of five particles/cell. CpG DNA 50 µg/ml, lipopolysaccharide (LPS) 100 ng/ml, recombinant HMGB-1 10 µg/ml (produced and purified as described previously; ref. [23
]), and interferon-
(IFN-) 100 U/ml (recombinant rat IFN-, a kind gift from Dr. Peter van der Meide, Utrecht University, The Netherlands) were applied to M cultures individually or in combination as indicated in figure legends. Cultures were supplemented routinely with Polymyxin B sulfate 20 µg/ml to inhibit contaminating endotoxin when Escherichia coli-derived HMGB-1 was used [15
].
Proliferation assay
For proliferative response of lymph nodes (LN), rats were anaesthetized and injected intradermally (i.d.) at the base of the tail with an emulsion containing 100 µg ovalbumin (OVA; Sigma) in IFA or CFA (containing 200 µg heat-killed M. tuberculosis H37Ra; Difco Labs). Draining LN-derived cells were recovered on day 5 postimmunization and restimulated in vitro with OVA (100 µg/ml) or concanavalin A (5 µg/ml) for 48 h with an additional 24 h after addition of [H3] thymidine. Cells were harvested using a Tomtec cell harvester, and incorporated radioactivity was counted using a ß-liquid scintillation counter, 1450 Microbeta Plus (Wallac Oy, Turku, Finland). Results are presented as stimulation indices (S.I.).
Immunohistochemical analysis of MHC class II up-regulation
M were cultured, stimulated [for 48 h with LPS (10 µg/ml)+IFN- (100 U/ml) or medium alone], fixed, and stained as described (R. Kokkola, Å. Andersson, G. Mullins, T. Östberg, C-J. Treutiger, B. Arnold, P. Nawroth, U. Andersson, R. A. Harris, H. Erlandsson Harris, in press). The number of cells staining positively for each group was counted for three separate fields containing 
400 cells each.
Quantification of nitrite in culture SNs
Measurement of NO2– SNs using the Griess reagent provides a surrogate marker and quantitative indicator of NO production. SNs from M, which had been incubated at a concentration of 105cells/ml with or without the indicated stimulants for up to 120 h, were analyzed. Samples were plated in triplicate wells of 96-well plates, mixed with an equal volume of freshly prepared Griess reagent (modified; G-4410 Sigma), and incubated for 15 min at room temperature. Absorbance was measured at 540 nm using a plate reader (LabSystems, Basingstoke, UK).
Enzyme-linked immunosorbent assay (ELISA) cytokine analyses
ELISA kits for detection of secreted TNF, IL-6, and IL-10 in culture SNs were purchased from Biosource (Camarillo, CA) and used according to the manufacturer’s instructions. In brief, SNs recovered from M, which had been incubated at a concentration of 105 cells/ml with or without the indicated stimulants for indicated times, were run in triplicate, and absorbance was measured at 450 nm.
Real-time polymerase chain reaction (PCR) and quantification of cytokines
Real-time PCR to quantify levels of rat IL-1ß, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), p40, p35, and p19 has been described previously [24
, 25
]. RNA isolation, subsequent cDNA preparation, and real-time PCR were performed as described previously [24
]. Amplification was performed using an ABI Prism 7700 sequence detection system (Perkin-Elmer, Norwalk, CT). The relative amounts of the endogenous control GAPDH mRNA and target mRNA in each sample could be deduced from the GAPDH and target mRNA standard curves, respectively. Standard curves were made using serial dilutions of cDNA from LPS-stimulated (100 ng/ml, 2.5 h, 6 h, and 12 h) rat M.
Western blot analyses of mitogen-activated protein kinase (MAPK) signaling pathways
M were plated at 2 x 106cells/well in six-well plates (Nunc) and incubated with the indicated stimuli for the indicated time intervals. Cells were thereafter lysed and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western immunoblotting with antibodies specific for GAPDH, phosphorylated-p44/42, phosphorylated-p38, and phosphorylated-stress-activated protein kinase 1 (SEK1)/MAPK kinase 4 (MKK4; all from Santa Cruz Biotechnology, Santa Cruz, CA) as described (R. Kokkola et al. in press).
Measurement of arginase activity
M were plated at 1 x 106cells/well in 12-well plates (Nunc) and incubated with LPS for 18 h. Cells were thereafter lysed with 100 µl 0.1% Triton X-100. After 30 min incubation on a shaker, 100 µl 10 nM MnCl2 and 100 µl 50 mM Tris-HCl (pH 7.5) were added to the sample. The arginase was then activated by heating the sample for 10 min at 56°C, and arginine hydrolysis was conducted by incubating 100 µl of the sample with 100 µl 0.5 M L-arginine (pH 9.7) at 37°C for 60 min. The reaction was stopped with 900 µl H2SO4 (96%)/H3PO4 (85%)/H2O (1:3:7 v/v/v), and the sample was mixed with 40 µl 9% isonitrosopropiophenone (dissolved in 100% ethanol). After heating at 95°C for 45 min, urea concentration was determined by spectrometry at 540 nm.
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cultures. No quantitative or qualitative (kinetic) differences in uptake of this fluid-phase tracer were recorded in DA, BN, or PVG M (data not included). Exogenous antigen presentation also relies on expression of MHC II molecules by APC during cell activation. Levels of MHC II were assessed immunohistochemically using specific antibodies following IFN-/LPS stimulation of M. The up-regulation of MHC II as compared with control was not statistically different regardless of origin (DA showed a 5.61-fold increase; PVG 6.95 and BN, 5.65). To indirectly assess these processing/presentation processes, the recall proliferative responses in LN cell cultures from DA, BN, and PVG rats were measured day 5 postimmunization with OVA in IFA or CFA by challenge in vitro with 100 µg OVA. Although proliferative responses were increased through the addition of mycobacterium to IFA in the autoimmune-susceptible DA strain, the opposite was true for the more autoimmune-resistant PVG and BN strains (Fig. 1 ).
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Figure 1. Differences in the proliferative response in lymph node cultures from DA, PVG, and BN rats, 5 days after immunization with OVA. Rats (n=3/group) were immunized i.d. with 100 µg OVA in IFA or CFA. Day 5-postimmunization, draining LN were removed and stimulated individually with 100 µg OVA, and the specific T cell proliferation was calculated. A representative of two individual experiments is presented. Data are means ± SD.
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from different strains.
Innate immune activation is greater and faster in autoimmune-resistant BN rats than in autoimmune-susceptible DA rats
Although the potential of M to interact with T cells appeared similar in DA and BN rat strains, we reasoned that there might be differential activation of these cells during innate immune responses that could impact on resulting activated T cell phenotypes. To address this issue, we challenged M from each strain with a variety of stimuli and measured induction of a panel of expressed products. Stimulatory challenges included agents known to cross-link different TLRs (LPS, yeast, CpG DNA), receptor for advanced glycation end products (HMGB-1), and cytokine (IFN-) receptors. Irrespective of the stimulus, the response pattern was different between autoimmune-susceptible DA and resistant BN rat strains.
Release of the proinflammatory mediators NO (Fig. 2a
and 2b
) and TNF (Fig. 2c
and 2d)
into the SN was assessed at intervals up to 120 h post-challenge. NO and TNF were less potently and more slowly released from DA (Fig. 2a
and 2c)
than from BN (Fig. 2b
and 2d)
M, irrespective of the stimulating challenge. There was little difference in the level of activation in BN M following stimulation with any of the applied ligands, and for DA M, application of zymosan, LPS alone, or HMGB-1 was less stimulatory than were IFN-, M. tuberculosis, and CpG DNA.
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Figure 2. NO and TNF are expressed at higher levels and have faster kinetics in autoimmune-resistant BN rats than in autoimmune-susceptible DA rats. NO2– (a, b) and TNF (c, d) in M culture SN (105cells/ml) from DA (a, c) and BN (b, d) rats (n=3/group) were measured using the Griess method (NO) or by ELISA (TNF) after stimulation with the indicated antigen for the indicated time-point. Results are representative of three independent experiments.
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, autoimmune-resistant strains respond more potently and with faster kinetics than do autoimmune-susceptible strains in production of proinflammatory mediators. However, the autoimmune-resistant BN M genetic program still requires activating receptor ligation for induction, as application of medium alone or latex beads (which are internalized through receptor-independent phagocytosis) failed to induce proinflammatory responses. Additionally, the repertoire of specific M receptors being ligated appears to differ between autoimmune-susceptible and -resistant strains, as some differences in patterns of activation were recorded with particular stimulants, indicating differing potentials for innate immune activation in both rat strains (compare levels of TNF production 8 h after stimulation with zymosan or CpG DNA).
MAPK intracellular signaling pathways are similarly activated in DA, BN, and PVG M
As LPS and IFN-, alone or in combination, were representative of innate immune activation stimuli, they were used in all subsequent experiments. The consequence of receptor ligation is usually activation of intracellular signaling cascades. Phosphorylation of the MAPK signaling elements p38, p44/42, SEK1/MKK4, and cJUN was thus compared in M from the different rat strains using specific Western blotting analyses following stimulation with IFN- and LPS. All signaling elements analyzed were equally phosphorylated in activated DA, PVG, and BN M with similar kinetics. The results for p38, p44/42, SEK1/MKK4, and GAPDH analyses of LPS-stimulated cells are presented in Figure 3
. Additionally, as SEK1/MKK4 and cJUN activation is associated with an activation cascade resulting in production of MMPs such as MMP9, which is implicated in tissue pathogenesis, MMP9 enzyme activity was assessed in activated M lysates using gelatin zymography, no difference in activity being recorded between strains (data not included). Taken together, these studies suggest that MAPK signal cascades can be similarly activated in autoimmune-susceptible and -resistant rat M and that differential MMP activities do not differentiate these two autoimmune phenotypes.
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Figure 3. MAPK signaling pathways are similarly activated in DA, PVG, and BN M. BM-derived M (BMM) were stimulated with LPS (100 ng/ml), and the phosphorylation of p38 MAPK, p44/42 MAPK, and SEK1/MKK4 was recorded at various time-points (0–60 min) by Western blotting technique. GAPDH, used as endogenous control, was equally expressed. Results are representative of three independent experiments.
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of different rat strains was the activation of different genetic effector programs resulting in classically or alternatively activated phenotypes. We thus measured arginase activity in M following activation with LPS. Arginase uses arginine as a substrate for production of ornithine, and NOS enzymes convert arginine to NO. The balance of NO/arginase activity is thus mutually regulated, and NO and arginase activities were measured in the same cultures. The data presented in Figure 4
demonstrate that although the percentage increase of NO secretion above baseline was higher in BN and PVG than in DA rat M (Fig. 4a) , the reverse was true for arginase activity, with a higher percentage increase in DA rat M (Fig. 4b)
. These results clearly demonstrate that an activation phenotype of autoimmune-susceptible DA rat M (low NO, high arginase) and of autoimmune-resistant BN and PVG rat M (high NO, low arginase) can be used to differentiate these strains.
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Figure 4. The increase of arginase activity above baseline is higher in DA than PVG and BN, and the reverse is true for NO secretion, with higher increases in PVG and BN rats. (a) NO2 levels in M culture SN (105cells/ml) from DA, BN, and PVG rats (n=3/group) were measured using the Griess method 72 h after stimulation with LPS (100 ng/ml). (b) Arginase activity was measured in cell lysates from M (106 cells) cultured in the absence or presence of LPS (100 ng/ml) for 18 h. Results are representative of three independent experiments. Data are means ± SD.
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activation by different stimuli were measured as a result of their pivotal roles in immunological responses. The levels of secreted TNF (Fig. 5a
), IL-10 (Fig. 5b)
, IL-6 (Fig. 5c)
, and IL-1ß transcripts (Fig. 5d)
were all higher in BN than in DA rat M. When IFN- was applied alone to these cultures, no significant induction of each cytokine was apparent. It is interesting that a combination of IFN-/LPS as stimulating agent abrogated secretion of IL-6 and IL-10 but not of TNF.
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Figure 5. Elevated TNF (a), IL-10 (b), IL-6 (c), and IL-1ß (d) production in M from autoimmune-resistant BN (a–d) and PVG (a, b), as compared with susceptible DA rat. TNF, IL-10, and IL-6 were measured in M culture SN (105cells/ml) with ELISA, after stimulation with indicated antigen for 6 (TNF) or 48 (IL-10 and IL-6) h. Total RNA was isolated 2.5 h after stimulation with LPS and analyzed for expression of IL-1ß mRNA using the Taqman technique. Results are representative of three independent experiments. Data are means ± SD. Ctrl, Control.
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following activation and that single or combinations of cellular activation may result in differential regulation of cytokine production.
The IL-12 and IL-23 subunits p35 and p19 are differentially expressed in autoimmune-susceptible and -resistant strains
In recent years, it has become understood that particularly important M-released mediators of inflammation are IL-12 and IL-23. They share the p40 subunit, but outcome of their production is diverse, where IL-23 (p40 assembled with p19) is associated with a prolonged inflammatory response, and IL-12 (p40 assembled with p35) is thought to be responsible for the initial inflammation [26
]. We therefore constructed primer pairs for the subunits p40, p35, and p19 and assessed expression of mRNA transcripts in activated M. Following stimulation with LPS, the expression of p40 was comparable in all three rat strains, whereas the expression of p35 and p19 subunits differed substantially (Fig. 6
). The higher expression of p35 in the relatively autoimmune-resistant rat BN would suggest a preferred formation of the IL-12 complex rather than IL-23, and the higher expression of p19 in DA rats indicates higher levels of IL-23. In contrast, PVG rats had the lowest production of both cytokine transcripts. Differential production of IL-23 and IL-12 can thus be used to phenotypically define autoimmune susceptibility in rat M.
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Figure 6. Differential expression of the IL-12 and IL-23 subunits p35 and p19 in M from autoimmune-resistant/-susceptible rat strains. High p35 and low p19 were expressed in M from BN rat, and the opposite was true for susceptible DA rat. In the PVG strain, a difference to the BN phenotype was the low expression of p35 and p19. Similar levels of p40 were detected in all three rat strains. Total RNA was isolated 2.5 h after stimulation with or without LPS and analyzed for expression of p40, p35, p19, and GAPDH mRNA using the Taqman technique. Results are representative of three independent experiments. Data are means ± SD.
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are also normally resident in tissues associated with autoimmunity. Once activated, M produce a variety of proinflammatory mediators and can present autoantigens to autoimmune T cells. Although dendritic cells are involved in the first induction of an autoimmune response, it is primarily M activity that leads to local tissue destruction and secondary T cell stimulation at sites of injury. Given this prominent role of M in autoimmune pathology, the differential strain susceptibility to experimental autoimmune disease exhibited by different rat strains might be a result of differences in properties of M in these strains. We thus extensively compared the responses to a variety of activating stimuli of BMM from three rat strains with different susceptibilities to autoimmune encephalomyelitis and arthritis.
Our studies revealed a number of important observations: There was no difference in antigen uptake and presentation between the strains nor was there a difference in the signaling pathways studied; M from autoimmune-resistant BN and PVG rats were more quickly and more potently activated than were M from autoimmune-susceptible DA rats; the balance of NOS and arginase activities is associated with autoimmune susceptibility/resistance; and the balance of IL-12 and IL-23 is also associated with autoimmune susceptibility/resistance.
Although there are a few reports comparing certain properties of M from selected strains of mice [27
, 28
] and many studies of mouse and rat M detailing investigation of the consequences of activation through specific stimulations, our study is the first, to our knowledge, that addresses a comparison of rat strains and a range of stimulatory agents and readouts. BMM were selected for study, as they represent a homogeneous cell population with little or no prior activation (compared with peritoneal M, which are heterogeneous and often already activated). Irrespective of the stimulus, the response pattern varied consistently between autoimmune-susceptible DA and -resistant BN and PVG rat strains. It is somewhat surprising that it was M from the autoimmune-resistant rather than the autoimmune-susceptible strains that produced the highest levels of classical, proinflammatory mediators (NO, TNF, IL-1ß, IL-6).
The major differences recorded among DA, BN, and PVG rat M following activation were in cytokine production and in the balance of NO/arginase production. The resultant phenotype representing autoimmune-susceptible DA rat M is lower TNF, IL-10, IL-6, IL-1ß, p35, and NO production with an associated high arginase activity and high expression of p19. Conversely, autoimmune-resistant BN M had a phenotype with higher TNF, IL-10, IL-6, IL-1ß, p35, and NO production with an associated low arginase activity and low p19 expression. In the PVG strain, a difference to the BN phenotype was the low expression of IL-12 and IL-23 subunit transcripts.
Disparate roles for NO in EAE have been defined as disease-inducing [29
] or disease-protective [30
, 31
]. As NO is linked to induction of apoptosis in T cells, the elevated production of NO following M activation in autoimmune-resistant BN and PVG strains could explain the reduced T cell proliferation recorded when mycobacteria were added to IFA on immunization as a result of differential T cell apoptosis sensitivity. The role of arginase in EAE/MS has been less well studied, but a recent gene array study analysis reported arginase I as the most significantly up-regulated gene in a MOG38–50-EAE model in C57BL/6 mice, and specific inhibition of arginase reduced disease severity [32
]. Additionally, a previous study in which administration of L-arginine significantly reduced disease in guinea pig spinal cord–EAE in Lewis rats was also associated with increased central nervous system (CNS)-NO levels [33
], indicating the therapeutic consequences of altering the balance of use of arginine by NOS/arginase. The activity of arginase I lowers the L-arginine concentration in the microenvironment, inducing NOS to produce O2– in addition to NO, the exclusive product of NOS at higher L-arginine concentrations [34
]. NO reacts with O2–, forming peroxynitrite (ONOO–), which is a highly reactive, oxidizing agent that modifies proteins and could cause damage to myelin proteins, in turn inducing autoimmune responses. Preferable formation of ONOO– as a result of arginase activity depleting arginine input into the NO pathway may thus be a potential mechanism to explain the association of arginase activity and autoimmune susceptibility. Indeed, ONOO–has been demonstrated to be a key contributor to MS and EAE, and administration of uric acid (natural antioxidant inhibiting ONOO–-mediated reactions) inhibits EAE [35
].
IL-23 is a cytokine recently described, which similarly to IL-12, promotes IFN- production and type-1, cell-mediated immunity, particularly in memory T cells [22
]. IL-23 rather than IL-12 has been demonstrated to be critical for experimental autoimmune inflammation in the joints [26
] and the CNS [36
, 37
], and viral [38
] and bacterial [39
] infection of human M induces an IL-23 response. Thus, IL-23 production is characteristic of chronic proinflammatory immune responses, and this is reflected by the preferential expression of p19 in autoimmune-susceptible DA rat M. It is interesting that M from the autoimmune-resistant PVG strain expressed the smallest numbers of p19 and p35 transcripts following activation, and this correlates well with the decisive role of these cytokines in development of autoimmune inflammation. It is interesting that IL-23 regulates expression of another cytokine associated with several chronic diseases including RA, psoriasis and MS, and IL-17, which is produced by activated memory T cells [40
]. In MS, increased expression of IL-17 is more specifically associated with relapse [41
]. Thus, our finding of a link between IL-23 and autoimmune susceptibility is also supported by these data linking IL-23, IL-17, and chronic inflammation states in humans and rodents.
Given that not only infiltrating monocytes from the blood but also resident M subpopulations might be involved in organ-specific autoimmune pathology, the activation phenotypes of BMM herein might not reflect the phenotypes of all M subpopulations in a given rat strain. Comparing and contrasting the functions of organ-specific subpopulations such as microglia (in EAE) or synoviocytes (in experimental arthritis) in different strains are thus now warranted.
Received July 5, 2004; revised August 12, 2004; accepted August 17, 2004.
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(TNF-) inhibitor (CNI-1493) in collagen-induced arthritis (CIA) in rats Clin. Exp. Immunol. 115,32-41[CrossRef][Medline]This article has been cited by other articles:
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