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

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Abstract
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 2×106. 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.