CD8-Positive T-Lymphocytes/drug effects; CD8-Positive T-Lymphocytes/immunology; Immune Tolerance/immunology; Transforming Growth Factor beta/pharmacology; Tretinoin/pharmacology; Adult; Aged; Aged, 80 and over; Animals; Antigens, CD/metabolism; CD4-Positive T-Lymphocytes/cytology; CD4-Positive T-Lymphocytes/immunology; CD4-Positive T-Lymphocytes/metabolism; CD8-Positive T-Lymphocytes/metabolism; CD8-Positive T-Lymphocytes/pathology; CTLA-4 Antigen; Cell Communication/immunology; Cell Count; Cell Proliferation; Coculture Techniques; Colitis, Ulcerative/immunology; Colitis, Ulcerative/pathology; Cytotoxicity, Immunologic/immunology; Dendritic Cells/immunology; Female; Forkhead Transcription Factors/genetics; Forkhead Transcription Factors/metabolism; Gene Expression/genetics; Gene Expression/immunology; Granzymes/genetics; Granzymes/metabolism; Green Fluorescent Proteins/genetics; Humans; Immunophenotyping; Interferon-gamma/metabolism; Interleukin-2 Receptor alpha Subunit/metabolism; Leukocytes, Mononuclear/pathology; Lymphocyte Activation/drug effects; Lymphocyte Activation/immunology; Male; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Middle Aged; Pore Forming Cytotoxic Proteins/genetics; Pore Forming Cytotoxic Proteins/metabolism; T-Lymphocyte Subsets/drug effects; T-Lymphocyte Subsets/immunology; T-Lymphocyte Subsets/metabolism