Inhibition of tumor growth by recognition factors

Hypothesis: blocking factors and human pregnancy: an alternative explanation for the success of lymphocyte transfusion therapy in abortion-prone women

Recent evidence has demonstrated that the non-specific immunosuppression that develops during pregnancy is not due to the de novo synthesis of immunosuppressive factors (ISF) but is a result of the activation of pre-existing molecules. The latter are present in normal sera as inactive complexes with a molecule which is specifically depleted following conception resulting in the activation of the ISF; the depleted molecule is termed the pregnancy-depleted immunoregulatory factor (pdIRF). Since non-specific ISF are detected in various diseases, it is proposed that the ISF-pdIRF relationship observed in pregnancy is a universal phenomenon and that the depletion of pdIRF and the activation of ISF can be achieved by a variety of stimuli. It is further proposed that abortion-prone women fail to adequately deplete their pdIRF levels so that the ISF are not activated. However, owing to the universal nature of the system, lymphocyte transfusion therapy supplies the necessary stimuli so that the pdIRF levels are depleted and the ISF activated which ensures a successful outcome to the pregnancy.

The effect of Kupffer cell stimulation or depression on the development of liver metastases in the rat

Tumour cells from a squamous carcinoma (approximately 2.5 X 10(5)) were injected intraportally into a syngeneic strain of rats to produce liver metastases 14 days later. Kupffer cells were stimulated by Corynebacterium parvum (7 mg or 1 mg i.v.) and zymosan (10 mg intraportally). Kupffer cell activity was depressed by the administration of silica, gadolinium chloride or human red cells. The animals in each group were sacrificed at 14 days, the livers removed and the number of visible surface metastases counted and compared. (Mann-Whitney U-test). Kupffer cell stimulation significantly reduced the number of surface liver metastases in all animals (P 0.0048). In contrast depression of Kupffer cell activity significantly increased the number of metastases in all animals (P 0.0045), suggesting that the activity of these cells has an important effect on the development of liver metastases.

Pregnancy-associated nonspecific immunosuppression: mechanism for the activation of the immunosuppressive factors

The nonspecific immunosuppressive effect observed in pregnancy sera and mediated by two factors, immunosuppressive factors (ISF) I and II, was regulated by a third molecule termed the pregnancy-depleted immunoregulatory factor (pdIRF). Natural depletion of serum pdIRF levels during pregnancy resulted in the activation of the ISF-I and ISF-II molecules, which prior to conception existed in the serum in inactive forms. The inactive ISF-I and ISF-II molecules in male sera and in nulliparous nonpregnant female sera can be activated following the artificial selective depletion of pdIRF by absorption onto Sephacryl S-300. It is proposed that inactive complexes consisting of the ISF-I and ISF-II molecules and pdIRF and possibly involving Ca2+ and Mg2+ ions are a feature of normal sera. The pdIRF molecule has an apparent Mr of 100,000-125,000 daltons and consists of a single major polypeptide of 63,000 daltons. Equal concentrations of pdIRF are present in male and female normal sera.

Circulating immunoreactive and bioassayable opsonic plasma fibronectin during experimental tumour growth

Immunoreactive and bioassayable plasma fibronectin (opsonic α(2) surface-binding (SB) glycoprotein) was measured during experimental Sarcoma-180 tumour growth in mice. Male C57BL/6 mice were challenged s.c. with 2 × 10(6) viable Sarcoma-180 tumour cells and evaluated sequentially in parallel with saline-injected controls over a 21-day experimental period. Before challenge, immunoreactive plasma fibronectin was 1050-1150 μg/ml. Minimal tumour growth occurred until 6 days after tumour challenge. There was then a rapid increase in primary tumour size, especially over the 7-14-day interval, with a plateau of growth over the 18-21-day interval. Immunoreactive plasma fibronectin was significantly (P < 0·05) raised at 3 and 7 days after tumour challenge. A rapid rise (P < 0·001) to 2816·6 ± 158·9 μg/ml was observed at 14 days followed by a modest decline at 21 days. Bioassayable opsonic activity increased (P < 0·5) with the rise in immunoreactive fibronectin 3 and 7 days after tumour challenge, but the rapid rise in immunoreactive fibronectin over the 7-14-day interval was associated with a significant (P < 0·5) fall in bioassayable opsonic activity. Thus, the rapid rise in immunoreactive plasma fibronectin parallels the rapid rate of tumour growth, but is associated with a fall in opsonically active plasma fibronectin. Dissociation between immunoreactive and opsonically active plasma fibronectin may be mediated by inhibition and/or alteration of circulating fibronectin during rapid tumour growth. Alternatively, it may reflect increased release of antigenically related protein (i.e. cell-surface fibronectin) during rapid tumour growth, which may have limited biological opsonic activity.

Mammary-carcinoma cells in mouse liver: infiltration of liver tissue and interaction with Kupffer cells

Interactions between TA3 mammary-carcinoma cells and liver cells were studied with the electron microscope in mouse livers that had been perfused with a defined medium containing the tumour cells. Infiltration of liver tissue by the TA3 cells proceeded in the following steps. First, numerous small protrusions were extended through endothelial cells and into hepatocytes. Next, some cells had larger processes deeply indenting hepatocytes. Finally a few tumour cells became located outside the blood vessels. Two variant cell lines, TA3/Ha and TA3/St, differing in cell coat and surface charge, did not differ in the extent of infiltration. TA3/Ha cells were often encircled by thin processes of liver macrophages (Kupffer cells). Encircled cells were initially intact, but later some of them degenerated. These observations suggest that TA3/Ha cells were phagocytized by the Kupffer cells. Encirclement appeared to be inhibited after only 30 min, when many cells were still partly surrounded. Encirclement of TA3/St was much less frequent. After injection of tumour cells intra-portally in vivo, similar results were obtained, which demonstrated the validity of the perfused liver model. TA3/Ha cells formed much fewer tumour nodules in the liver than TA3/St cells.

Decreased resistance to intravenous tumour-cell challenge during reticuloendothelial depression following surgery

The influence of surgical stress on resistance to i.v. challenge with Walker 256 tumour cells was investigated in rats, with respect to the functional state of the reticuloendothelial system (RES). Phagocytic activity of the RES was evaluated by colloid (gelatinized [131I] "RE test lipid emulsion") clearance, and opsonin levels were determined by bioassay. Reticuloendothelial clearance capacity was significantly (P less than 0-05) depressed 60 min following surgery (coeliotomy plus jejunal enterotomy) as quantified by both humoral and cellular parameters of RE function. Phagocytic depression was primarily due to impaired hepatic Kupffer cell function and related to a deficiency in the phagocytic supporting capacity of plasma, also referred to as opsonic or recognition factor (RF) capacity. During the postoperative period of RES colloid clearance depression, pulmonary localization of the blood-borne test particulate matter increased. Rats challenged with 51Cr-labelled viable tumour cells at a dose of 1-0 X 106 i.v., either prior to or during the postoperative period of RE depression, manifested a significant (P less than 0-05) increment in pulmonary localization of the viable tumour cells, and a decrease (P less than 0-05) in hepatic clearance. Evaluation of survival patterns demonstrated a significant (P less than 0-01) decrease in host resistance to i.v. tumour cell challenge (2 X 103 cells) during the postoperative period of RE depression and hypo-opsonaemia. Sham-anaesthetized control animals survived 17-9 +/- 0-8 days, while animals challenged during the period of RE depression survived 7-9 +/- 0-4 days. An increased incidence of respiratory distress and nasal discharge was observed in the animals with impaired survival. Thus, surgical manipulation may transiently compromise RES systemic host defence and may be reflected in an increment in the pulmonary localization of blood-borne tumour cells. The relationship of this altered pattern of tumour cell distribution to the impaired survival remains to be determined, and warrants investigations.

Humoral mediated macrophage response during tumour growth

Reticuloendothelial (RE) phagocytic and circulating plasma opsonic activity was evaluated in rats transplanted with the Walker 256 carcinoma tumour in an attempt to evaluate the role of opsonic protein in governing the functional state of the macrophage system. Animals transplanted intramuscularly with 2 X 10(4) viable tumour cells manifested 2 peaks of RE stimulation at 6 and 14 days post-transplantation with a subsequent decline in the phagocytic activity over the 14-30 day period. Increased phagocytic activity as determined by colloid clearance was primarily a reflection of hepatic Küpffer cell hyperphagocytosis while the decline in phagocytic activity was related to a decrease in Küpffer cell function. The initial peak of RE stimulation was associated with an elevation in the blood opsonin level and no significant enlargement of the liver and spleen. In contrast, the second peak of RE stimulation at 14 days was associated with both an elevation in opsonin levels and an associated hepatic and splenic enlargement. The decline in phagocytic activity over the 14-30 day interval was associated with a progressive decline in the plasma opsonic activity, a return of the spleen to its normal size in relationship to the body weight, and a persistent hepatomegaly. These findings suggest that the alterations in macrophage function during tumour growth may be mediated in part by changes in the opsonic or phagocytosis promoting capacity of plasma. Since opsonic protein contributes to the discriminatory capacity of macrophages, it is suggested that changes in the blood opsonin level may condition the anti-tumour capacity of the macrophage system with respect to host defence aginst malignant disease.