Induction of suppression by a murine nonspecific suppressor-inducer cell line (M1-A5). III. Partial purification of the suppressor cell-inducing factors.

The cause of the state of anergy which often accompanies advanced tumor growth has been attributed to several factors, including nonspecific suppressor cells capable of suppressing humoral and cell-mediated responses. Induction of suppressor cells in tumor-bearing hosts has been attributed to the release of immunoregulatory factors by the tumor, as well as by the host's own lymphoid cells. Several such "suppressor cell-inducing factors" have been described. However, in only a few cases has the inducing material been characterized. We have recently reported the existence of a suppressor cell inducing factor (SIF) in the 18 hr culture supernatant of spleen cells from mice bearing an advanced M-1 fibrosarcoma. Our aim was to characterize SIF, both biochemically and mechanistically. In order to purify the inducing factor, as well as to dissect the cellular and molecular events that occur as a result of suppressor cell activation, we isolated the M1-A5 cell line from the spleen cells of a mouse bearing an advanced M-1 fibrosarcoma. Induction of suppressor cells by supernatants from M1-A5 cells closely resembled the situation seen with the whole spleen cells. In both cases: 1) an inducing factor with an estimated Mr less than 12 kDa was found, and 2) the release, but not the effector function, of the inducing factor was prostaglandin-dependent. The 18 hr culture supernatant of M1-A5 cells was used as the source of the inducing factor and suppressor cells were activated by exposure of normal spleen cells to the inducing factor for 4 hr. The nature of the inducing factor was investigated by subjecting the M1-A5 culture supernatant to molecular weight sieving on Sephadex G-100 medium. The results showed that M1-A5 supernatants contained a high- (Mr 70 kDa) and a low- (Mr 5.5 kDa) molecular weight factor, which were termed SIF alpha and SIF beta, respectively. SIF alpha and SIF beta were further purified by ion exchange chromatography. SIF beta bound to QAE-Sephadex A-25 and was eluted in a single peak. However, SIF alpha displayed heterogeneity with respect to binding to DEAE-Sephacel, as SIF activity was seen in the void volume as well as in fractions eluted from the anionic exchanger. Mechanistically, we demonstrate that the induction of suppressor cells by SIF alpha and SIF beta is genetically non-restricted. In addition, we show that SIF alpha and SIF beta suppress the in vivo antibody response to sheep red blood cells.(ABSTRACT TRUNCATED AT 400 WORDS)