A single amino acid determines the immunostimulatory activity of interleukin 10.
Cellular interleukin 10s (cIL-10s) of human and murine origin have extensive sequence and structural homology to the Epstein-Barr virus BCRF-I gene product, known as viral IL-10 (vIL-10). Although these cytokines share many immunosuppressive properties, vIL-10 lacks several of the immunostimulatory activities of cIL-10 on certain cell types. The molecular and cellular bases for this dichotomy are not currently defined. Here, we show that the single amino acid isoleucine at position 87 of cIL-10 is required for its immunostimulatory function. Substitution of isoleucine in cIL-10 with alanine, which corresponds to the vIL-10 residue, abrogates immunostimulatory activity for thymocytes, mast cells, and alloantigenic responses while preserving immunosuppressive activity for inhibition of interferon gamma production and prolongation of cardiac allograft survival. Conversely, substitution of alanine with isoleucine in vIL-10 converts it to a cIL-10-like molecule with immunostimulatory activity. This single conservative residue alteration significantly affects ligand affinity for receptor; however, affinity changes do not necessarily alter specific activities for biologic responses in a predictable fashion. These results suggest complex regulation of IL-10 receptor-ligand interactions and subsequent biological responses. These results demonstrate that vIL-10 may represent a captured and selectively mutated cIL-10 gene that benefits viral pathogenesis by leading to ineffective host immune responses. The ability to manipulate the activity of IL-10 in either a stimulatory or suppressive direction may be of practical value for regulating immune responses for disease therapy, and of theoretical value for determining what aspects of IL-10 activity are important for normal T cell responses.
Ding
Y
Y
Department of Microbiology and Immunology, The University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA.
Qin
L
L
Kotenko
S V
SV
Pestka
S
S
Bromberg
J S
JS
D000409:Alanine / Q000276:immunology; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D019556:COS Cells; D002455:Cell Division; D002478:Cells, Cultured; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D007108:Immune Tolerance; D016753:Interleukin-10 / Q000737:chemistry / Q000276:immunology*; D007532:Isoleucine / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008894:Milk Proteins; D008969:Molecular Sequence Data; D018123:Receptors, Interleukin / Q000276:immunology / Q000378:metabolism; D053701:Receptors, Interleukin-10; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000378:metabolism
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D018123:Receptors, Interleukin; D053701:Receptors, Interleukin-10; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D050799:STAT5 Transcription Factor; C494080:Stat1 protein, mouse; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D007532:Isoleucine; D016753:Interleukin-10; D000409:Alanine