Soluble suppressor factors elaborated in experimental malignant ascites

Abstract

Soluble suppressor factors in the sera of cancer patients inhibit lectin-stimulated lymphocyte proliferation. These factors, derived from human material, preclude easy corroboration by other investigators. To gain a general understanding of soluble suppressor factors and to avoid the necessary restrictions of human experimentation, an animal model was devised. Sprague-Dawley rats were injected ip with the Walker 256 carcinoma. The resultant ascites proved to be a stable, reproducible source of soluble suppressor factors. Ascites inhibited phytohemagglutinin (PHA)-induced blastogenesis of normal splenccytes by 98%. The possibility of a toxic effect was eliminated by vital staining of splenocytes and by examination in a specific lymphotoxin assay. Suppressor activity persisted after heating at 100°C for 40 min. Extraction by lipid solvents revealed that the bulk of suppressor activity resides in the lipid phase. The active fraction of heat-treated ascites passed through an Amicon PM-10 filter. Thin-layer chromatography revealed the presence of prostaglandins E2 and F2.. Tissue culture supematants from short-term cultures derived from tumor-bearing animals revealed suppressor activity from thymus, spleen, and liver cultures (97, 9 1, and 7 I %, respectively). No suppressor activity was detected in cultures of cancer cells. This study has demonstrated in this animal model that prostaglandins play a major role in suppression of lectin-induced blastogenesis. All suppressor factors appear to be host derived. An understanding of the mechanism of release of these suppressor substances may open new avenues in the immunotherapy of cancer.

Plasma ultrafiltration as successful therapy of rabbit VX‐2 carcinoma

“…Previous work in our laboratory demonstrated a similar inhibition of lymphocyte blastogenesis by suppressors of host origin present in the sera and ascites of rats bearing the Walker 256 carcinoma [7,11]. Although a number of suppressors in this model can be separated by molecular sieving and polyacrylamide gel electrophoresis Recognizing that soluble suppressors or "blocking factors" may be present in the serum of cancer patients, clinicians have instituted large-volume plasma exchanges [ 19,201 or passage of autologous plasma over immobilized staphyloccal protein A [21 J as a means of reducing suppressor activity.…”

“…Our laboratory has partially characterized multiple components of malignant ascites in rats capable of inhibiting in vitro lectin-stimulated lymphocyte blastogenesis. Several of these molecules are heat labile and of low molecular weight (< 10 kD) [7,11]. These low molecular weight suppressive factors appear in the sera of tumor-bearing animals shortly after tumor inocu-…”

Heterogeneity of Soluble Suppressor Factors in Rat Malignant Ascites

“…The details of this assay have been described previously [8]. Briefly, splcnocytcs from a normal spleen obtained from a healthy donor were suspended in RPMI 1640 supplemented with 10% fetal calf serum and the cell concentration adjusted to 5 x 10ft viable cells/ml.…”

“…In addition, therapeutic manipulation with chemothera peutic agents, radiation, and surgery may perturb the natural host immune response complicating inter pretation of experimental data [4][5][6][7]. In order to cir cumvent these problems we have investigated an ani mal model capable of generating large quantities of soluble suppressor factors [8].…”