Impact of type-I-interferon on monocyte subsets and their differentiation to dendritic cells: An in vivo and ex vivo study in multiple sclerosis patients treated with interferon-beta
Introduction
Monocytes constitute between 3% and 7% of peripheral blood leukocytes. They derive from progenitors in the bone marrow, circulate in the blood as monocytes, and in tissue can differentiate into either macrophages or dendritic cells. The classical immunophenotypic marker for monocytes is CD14, the lipopolysaccharide receptor. Within this population, about 10% co-express CD16 (the low-affinity Fc-gamma receptor III). Since the first description of this CD14+CD16+ monocyte subpopulation, we have been able to show that they express (1) higher levels of MHC class II (Ziegler-Heitbrock et al., 1993), (2) little or no IL-10 mRNA in response to LPS-stimulation (Frankenberger et al., 1996), but (3) comparable levels of induced TNF-alpha mRNA (Frankenberger et al., 1996) and higher levels of TNF-alpha protein (Belge et al., 2002), compared to the “classical” (CD14+CD16−) monocytes. We have therefore termed them “pro-inflammatory monocytes.” Consistent with this notion, an expansion of the CD14+CD16+ population has been found in septicemia (Fingerle et al., 1993), erysipelas (Horelt et al., 2002), AIDS and other infectious or inflammatory disorders (Ziegler-Heitbrock, 1996).
Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). There is ample evidence to support an autoimmune pathogenesis of MS, crucially dependant on autoreactive T lymphocytes (Hohlfeld et al., 1995). Despite some variation among patients Brück et al., 1995, Lucchinetti et al., 2000, the inflammatory lesions in the CNS white matter commonly contain considerable numbers of macrophages. While there is currently no cure for MS, acute exacerbations can be effectively treated with a pulse of high-dose glucocorticoids (Miller et al., 2000), and chronic interferon beta (IFNb) treatment reduces relapse frequency and disease progression (Goodin et al., 2002). We have previously shown that intravenous glucocorticoids selectively deplete the pro-inflammatory monocytes from the peripheral blood of MS patients (Fingerle-Rowson et al., 1998), which may contribute to the drug's rapid anti-inflammatory effect. Here, we examined if the established long-term treatment with IFNb also has an effect on monocyte subsets.
The CD14+CD16+ subset of peripheral blood monocytes is also thought to be a transitional stage in the development of monocytes to either macrophages or dendritic cells Ziegler-Heitbrock et al., 1993, Siedlar et al., 2000, de Baey et al., 2001. Within this population, those cells with low levels of CD14 appear to develop into dendritic cells Siedlar et al., 2000, de Baey et al., 2001. We demonstrated in MS patients that IFNb will shift the CD14+CD16+ towards higher expression of CD14. This may skew the developmental potential of monocytes in favour of macrophages, at the expense of dendritic cells. In fact, several in vitro studies suggest that IFNb inhibits development and function of dendritic cells Bartholome et al., 1999b, McRae et al., 2000b, Duddy et al., 2001, Wiesemann et al., 2002, but these observations have not been confirmed in vivo. We therefore studied the effect of IFNb on ex vivo generation of dendritic cells and suggest that IFNb treatment inhibits the formation of dendritic cell precursors from monocytes.
Section snippets
Overall design
Patients with clinically definite multiple sclerosis (Poser et al., 1983) of at least 18 years of age, who presented to the outpatient clinic of the Institut für Klinische Neuroimmunologie, were included in an open study. Patients were required to be free of corticosteroid medication for at least 2 months before any blood sampling. We excluded patients with other inflammatory or infectious diseases, any severe general medical illness or abnormal results of a routine laboratory investigation
MS patients have normal absolute and relative numbers of peripheral blood monocytes
In a cross-sectional study, we first analyzed absolute and relative numbers of peripheral blood monocyte subsets in 94 MS patients (Table 1). The absolute and relative numbers were in the range of previously published values (Ziegler-Heitbrock, 1996). In untreated patients, no significant differences were found according to the clinical course of the disease (relapsing-remitting (RR), secondary-progressive (SP) or primary-progressive (PP)), although patients with the primary progressive form
Discussion
In this open study in multiple sclerosis patients, we report that treatment with interferon-beta is associated with a shift toward higher CD14 expression on the pro-inflammatory subset of peripheral blood monocytes. Further, we demonstrate that IFNb appears to inhibit the formation of monocyte-derived progenitors for dendritic cells in vivo, and decreases their further differentiation in vitro.
Acknowledgements
The authors would like to thank Dr. R. Hohlfeld for continued support at all phases of the study and for critically reviewing the manuscript. We would also like to thank Dr. A. Yassouridis for reviewing the statistical procedures. This work was supported by a grant from the Deutsche Forschungsgemeinschaft (DFG ZI 288/2) to LZH and an unrestricted research grant from Serono Deutschland GmbH to the Institute of Clinical Neuroimmunology.
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