PARTIAL-PURIFICATION AND CHARACTERIZATION OF A NOVEL HUMAN FACTOR THAT AUGMENTS THE EXPRESSION OF CLASS-I MHC ANTIGENS ON TUMOR-CELLS

A cytokine which augments the expression of major histocompatibility c omplex (MHC)I antigens on K562 and gastric carcinoma tumour (HR) cells , has been isolated from the culture supernatant of Concanavalin-A (Co n-A) activated human peripheral blood mononuclear cells. The factor, t ermed MHC augmenting factor (MHC-AF) has been partially purified by Se phadex G-100 column chromatography, preparative isoelectric focusing a nd HPLC with ion-exchange as well as sizing columns. MHC-AF activity i s associated with a 35 kDa molecule which has pI of 6.0. Interferon (I FN)-alpha, beta, tumour necrosis factor (TNF), Interleukin (IL)-2, IL- 4, IL-5 and IL-7 had no significant effect in MHC-AF bioassay, but IFN -gamma had significant MHC-AF activity. Antibodies to IFN-alpha, IFN-b eta and TNF-alpha did not block the activity of MHC-AP, but anti-IFN-g amma antibodies could partially neutralize the activity. However, unli ke IFN-gamma, MHC-AF activity was resistant to pH 2.0 treatment. Purif ied MHC-AF preparations did not have any activity in WISH cell/encepha lo myocarditis virus (EMC) IFN bioassays. In addition, anti-IFN-gamma affinity column did not retain MHC-AF activity. These results indicate that a MHC-AF distinct from IFN-gamma, is produced by activated human mononuclear cells.