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The release of newly produced B and T lymphocytes from the production sites was analyzed in 30 multiple sclerosis patients treated with interferon-beta by measuring T-cell receptor excision circles and k-deleting recombination excision circles. We found that the therapy induces opposite effects on B- and T-cell mobilization in 33% of patients. New B-cell production, which peaks after 6months of therapy and then decreases to levels that, however, are still higher than in controls, may cause a renewal of the B-cell compartment. On the contrary, the decreased number of newly produced T lymphocytes observed at 12months of treatment and the association between reduced thymic output and low peripheral T lymphocytes can be a cause of leukopenia, a frequent side effect of the therapy.

Background: Interferon-beta is used to reduce disease activity in multiple sclerosis, but its action is incompletely understood, individual treatment response varies among patients, and biological markers predicting clinical benefits have yet to be identified. Since it is known that multiple sclerosis patients have a deficit of the regulatory T-cell subsets, we investigated whether interferon-beta therapy induced modifications of the two main categories of regulatory T cells (Tregs), natural and IL-10-secreting inducible Tr1 subset, in patients who are biologically responsive to the therapy. Methods: T-cell phenotype was determined by flow cytometry, while real-time PCR was used to evaluate interferon-beta bioactivity through MxA determination, and to measure the RNA for IL-10 and CD46 molecule in peripheral blood mononuclear cells stimulated with anti-CD46 and anti-CD3 monoclonal antibodies, which are known to expand a Tr1-like population. Results: Interferon-beta induced a redistribution of natural Treg subsets with a shift of naive Tregs towards the 'central memory-like' Treg population that expresses the CCR7 molecule required for the in vivo suppressive activity. Furthermore, in a subgroup of treated patients, the CD46/CD3 co-stimulation, probably through the Tr1-like subset modulation, increased the production of RNA for IL-10 and CD46. The same group showed a lower median EDSS score after two years of therapy. Conclusions: The selective increase of 'central memory-like' subset and the involvement of the Tr1-like population may be two of the mechanisms by which interferon-beta achieves its beneficial effects. The quantification of RNA for IL-10 and CD46 could be used to identify patients with a different response to interferon-beta therapy.