ABSTRACT
It was found that the suppressive activity of PNA~+ cells was mediated by asoluble factor which can be abrogated in the supernatant by pretreating with anti-Thy-1 serum plus complement.Thus,the suppressor factor here mentioned must becontributed to being a product of T cell line,putatively being defined as T suppres-sor factor(TsF).Physicochemical analysis revealed that this factor was heat-stableat 56℃ and not affected by acidification to pH 2 or alkalization to pH 11,but inac-tiviated at 100℃ or after 2-Mercaptotoethanol reduction.As indicated in enzymaticdigestion test,this suppressor factor was sensitive to trypsin but resistant to RNase.Therefore,it may be considered to be one kind of protein(or polypeptide)at least inpart.The approximate molecular weight of which was 50 KD,as deduced by Sepha-dex G 100 gel filtration.Specific oligosaccharide blocking test confirmed the factthat the suppressive effect on LxGvHR was able to be blocked by N-acetyl-glucosa-mine.And also,the suppression on PFC response was able to be eliminated by L-rha-mnose.It was still found that both of the cell synthesis and/or the release of the suppre-ssive factor was able to be blocked by adding Sodium Azide or Cytochalasin B tothe media initially.The in vitro induction experiment indicated that highly activesuppressive factor can be harvested from the supernatant in normal mice derivedPNA~+ cells briefly exposed to cell-free tumor cultures.After the factor was absor-bed onto relevant viable tumor cells,the residual suppressive activity was found tobe diminished.The suppressor factor-mediated suppression was MHC(H-2)restricted,for it cannot exert its action on target cells bearing incompatible H-2 products.As faras the immunological features concerned above,there must exist tumor-specific TsFwith antigen binding site as well as H-2 determinants.