Soluble Immune Response Suppressor (SIRS) Mediated Inhibition of Cell Division

Abstract

Soluble immune response suppressor (SIRS) is an immunosuppressive lymphokine produced by activated suppressor T lymphocytes.⁽¹⁾ The purified murine protein obtained from a T-cell hybridoma exhibits considerable heterogeneity and four different isoforms have been identified based on retention time on a reversed phase C-8 column and on isoelectric points. Activities eluting from reversed phase columns have been designated as SIRSα and SIRSβ. SIRSα. is further subdivided into three isoforms with isoelectric points of 5, 6, and 7 respectively, whereas SIRSβ only has an isoelectric point of 7. Each protein has a molecular weight of 11,000⁽²⁾. The biological activities of purified SIRSα-6 have been most fully characterized and include: 1) inhibition of tumor cell growth in vitro and in vivo, 2) inhibition of plaque-forming cell responses in vivo and in vitro, 3) inhibition of antigen dependent T-ce1I-clones, 4) inhibition of certain activities if IL1, and,5) inhibition of IL2 dependent proliferation of CTLLL⁽¹⁾.