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Tumor-derived suppressor factors (TDSFs) in normal and neoplastic colon and rectum
Abstract:
Acid tumor-derived suppressor factors (TDSFs, isoelectric pH less than 3.0) in extracts of murine fibrosarcomas and human colorectal adenocarcinoma cell lines induce normal murine spleen cells to inhibit delayed-type hypersensitivity (DTH) to the sensitizer dinitrochlorobenzene (DNCB). We sought to determine if TDSF from normal and neoplastic human colon and rectum also inhibited normal human peripheral blood mononuclear cells (PBMC) responses to mitogen and to alloantigens. Collagenase-DNase digests of five freshly isolated carcinomas and paired autologous normal tissues were subjected to preparative isoelectric focusing (pIEF) over a pH range of 2.5 to 9.5. Fractions with isoelectric pH less than 3.0 from three of the five tumors induced normal C3H/HeN spleen cells to inhibit DTH to DNCB. Acid fractions from three tumors and four normal tissues also significantly inhibited the PBMC proliferative response to mitogen and alloantigens. However, the ability of acid fractions to suppress lymphocyte proliferation did not correlate with the induction of suppression of DTH to DNCB. Incubation of human PBMC with acid proliferation inhibitors did not induce suppressor cells that would inhibit the subsequent proliferative response of fresh, autologous PBMC. The acid suppressant from colorectal carcinoma was sensitive to treatment with trypsin but not RNase or DNase, whereas murine TDSF is sensitive to RNase and resistant to treatment with trypsin. The suppressive moiety from one tumor had an apparent mass of 45 kDa by gel filtration chromatography, in contrast to murine TDSF that has a mass of more than 300 kDa. Thus, the acid inhibitor in digests of human colorectal carcinoma is distinct from the TDSF that induces suppressor cells for DTH to DNCB.
Insights
Acidic factors from human colorectal tumors suppress immune cell proliferation. These factors differ from murine tumor-derived suppressor factors (TDSFs) that inhibit delayed-type hypersensitivity (DTH) responses.
Area of Science:
- Immunology
- Oncology
- Biochemistry
Background:
- Acidic tumor-derived suppressor factors (TDSFs) from mouse fibrosarcomas and human colorectal cancer cell lines inhibit delayed-type hypersensitivity (DTH) in murine spleen cells.
- The nature and function of similar acidic factors in human colon and rectal tissues, both normal and neoplastic, remain to be fully elucidated.
Purpose of the Study:
- To investigate whether acidic factors from human colon and rectal tissues (normal and cancerous) can inhibit the response of normal human peripheral blood mononuclear cells (PBMC) to mitogens and alloantigens.
- To characterize the properties of these acidic suppressive factors and compare them to known murine TDSFs.
Main Methods:
- Preparative isoelectric focusing (pIEF) of collagenase-DNase digests from five human colorectal carcinomas and paired normal tissues.
- Assays to evaluate the inhibition of DTH in murine spleen cells and PBMC proliferation in response to mitogens and alloantigens.
- Biochemical characterization including sensitivity to trypsin, RNase, DNase, and gel filtration chromatography.
Main Results:
- Acidic fractions (pI < 3.0) from three of five human tumors induced suppression of DTH in murine spleen cells.
- Acidic fractions from three tumors and four normal tissues significantly inhibited PBMC proliferation.
- The suppressive activity on PBMC proliferation did not correlate with DTH suppression, and the human colorectal carcinoma acid inhibitor was trypsin-sensitive with a mass of 45 kDa, unlike murine TDSF.
Conclusions:
- An acidic factor in human colorectal carcinoma digests inhibits PBMC proliferation and is distinct from the murine TDSF that induces DTH suppressor cells.
- The human colorectal carcinoma acid inhibitor exhibits different biochemical properties (protease sensitivity, molecular mass) compared to murine TDSF.
- This suggests a novel mechanism of immune suppression associated with human colorectal cancer.