Humoral immune responses to tumor-specific antigens in strain-2 guinea pigs

Resistance of guinea-pig hepatoma cells to complement-mediated lysis induced by ascites fluid or serum from tumor-bearing animals

The mechanisms of tumor cell susceptibility and resistance to cytotoxic antibodies were investigated in the guinea-pig ascites hepatoma (line-1 and line-10) system. Treatment of line-specific rabbit antibody-coated tumor cells by ascitic fluid, by serum of tumor bearers or by tumor extract inhibited subsequent complement-mediated lysis. Inhibition by ascitic fluid and serum was not line-specific, but inhibition by tumor extract was line-specific. Treatment of tumor cells with ascitic fluid or tumor extract prior to exposure to specific cytotoxic antibody and complement did not inhibit lysis. Incubation of cytotoxic rabbit antisera with ascitic fluid, tumor-bearer serum or tumor extract neutralized their complement-dependent cytotoxic activity on tumor cells. Tumor-immune guinea-pigs exhibited line-specific delayed cutaneous reactions after injection with ascitic fluid or tumor extract. Studies with indrect immunofluorescence revealed that exposure to ascites fluid or tumor extract caused a rapid shedding of rabbit antibodies from the tumor cell surface. Evidence is presented indicating that the active fraction of ascites fluid was associated with immune complexes consisting of IgG and tumor antigen in excess. The relevance of these findings to tumor escape from immune destruction in vivo is discussed.

Immunogenicity of solubilized tumor antigen extracted from P1798 murine lymphoma cells or isolated from tumor-bearer ascites fluid and reactivity with anti-thy-1.2 antiserum

Solubilized antigen was prepared from P1798 lymphoma cells by sonication, 3 M KCI extraction, or isolated from the ascites fluid of syngeneic tumor-bearing BALB/c mice. Antigen was detected and quantitated by its ability to block activity of anti-P1798 serum raised in syngeneic mice, as assayed by cytotoxic and indirect immunofluorescence tests. It was established that the reaction was immunologically specific as the P1798 antigen did not inhibit the binding to L1210 lymphoma cells of antisera raised against L1210 in syngeneic DBA/2 or allogeneic BALB/c mice. Vaccination of BALB/c mice with different subcellular fractions of sonicated antigen or with ascites fluid resulted in protection against a live P1798 challenge with results comparable to those obtained using iodoacetamide-modified tumor cells. Solubilized antigen prepared by each of the three methods eluted from a Bio-Gel A5m agarose column exclusively in an early peak that had a molecular weight estimated to be greater than 2 X 10(6). This column-fractionated antigen was shown to cross-react with antiserum raised against Thy-1.2 antigen, which is present on P1798 cells. The purified P1798 antigen sedimented at 200,000 g and was shown to protect syngeneic mice in immunoprophylactic tests.

Serum factors modifying cell mediated immunity to rat hepatoma d23 correlated with tumour growth

Sera from rats bearing a progressively growing transplanted aminoazo-dye-induced hepatoma (hepatoma D23) have been examined for the presence of hepatoma D23-specfic antigen, antibody and immune complexes throughout the course of tumour growth. The levels of these factors have been correlated with the in vitro blocking and inhibition of cytotoxic lymph-node cells from immunized animals for cultured tumour cells. Sera from animals bearing small tumours (7-14 days after tumour implantation contain free tumour-specific antigen whilst immune complexes could not be detected. Although these sera were neither blocking nor inhibitory under the normal conditions of the test, when concentrated two and fourfold, inhibition but not blocking of lymph-node cell cytotoxicity could be detected. In comparison sera from animals bearing large tumours (24-28 days) blocked but did no inhibit in vitro lymph-node cell cytotoxicity and this correlates with the presence of tumour-specific immune complexes in antibody excess. Animals with intermediate-sized tumours had high levels of both blocking and inbibitory activity in the serum, these effects becoming apparent when neither free antibody nor free antigen could be detected. The relevance of these findings to the mechanism by which a growing tumour may escape specific cellular immune destruction is discussed.