Increased and highly stable levels of functional soluble interleukin-6 receptor in sera of patients with monoclonal gammopathy - Gaillard, J-P; Bataille, R; Brailly, H; Zuber, C; Yasukawa, K; Attal, M; Maruo, N; Taga, T; Kishimoto, T; Klein, B (Eur J Immunol, 1993)