Adjuvants, Immunologic/pharmacology; Cytokines/drug effects; Interferon-beta/pharmacology; Multiple Sclerosis/drug therapy; Pentoxifylline/pharmacology; Phosphodiesterase Inhibitors/pharmacology; T-Lymphocytes/drug effects; Adjuvants, Immunologic/therapeutic use; Base Sequence; Cells, Cultured; Chi-Square Distribution; Cytokines/biosynthesis; Dose-Response Relationship, Drug; Drug Synergism; Drug Therapy, Combination; Humans; Interferon beta-1a; Interferon beta-1b; Interferon-beta/therapeutic use; Interferon-gamma/antagonists & inhibitors; Interferon-gamma/biosynthesis; Interleukins/blood; Lymphotoxin-alpha/antagonists & inhibitors; Lymphotoxin-alpha/biosynthesis; Multiple Sclerosis/metabolism; Pentoxifylline/therapeutic use; Phosphodiesterase Inhibitors/therapeutic use; Polymerase Chain Reaction; Prospective Studies; RNA, Messenger/isolation & purification; T-Lymphocytes/metabolism; Tumor Necrosis Factor-alpha/antagonists & inhibitors; Tumor Necrosis Factor-alpha/biosynthesis; Up-Regulation