Kei Tsuzurahara

Divalent 5S fragments obtained from rabbit IgG antibodies by tryptic hydrolysis

Abstract Rabbit IgG antibodies against bacterial α-amylase were treated with trypsin in a medium free of any added reducing agent. The 5S fragments were isolated from the tryptic digest by fractionation with ammonium sulfate followed by gel filtration through Sephadex G-100 and were subsequently characterized in various ways. The tryptic 5S fragments could (1) form specific precipitate with corresponding antigen, (2) neutralize amylase actity, (3) react with anti-Fab but not with anto-Fc sera, (4) failed to induce passive cutaneous anaphylaxis in guinea pig. The 5S fragments (5) were separated into two populations by chromatography on carboxymethyl-cellulose, (6) differed in electrophoretic mobility from the original IgG, and (7) upon treatment with cysteine were split into 3·5S univalent fragments. The tryptic 5S fragments closely resembled the peptic 5S fragments with respect to antigenic structure and sedimentation characteristics.

Study on the mechanism of immunopotentiating antitumor effect of 6-MPG, a water-soluble derivative of 6-mercaptopurine

We investigated possible mechanisms of the antitumor action of gamma-(9H-purine-6-yl) thiomethyl L-glutamate (6-MPG), a water-soluble derivative of 6-MP. In the double grafted tumor system, BALB/c mice were inoculated intradermally with 10(6) cells of MethA fibrosarcoma at the right inguinal region on day 0 (the primary tumor) and later with 3 x 10(6) cells at the left on day 10 (the secondary tumor). Intraperitoneal administration of 6-MPG at a dose of 100 mg/kg/day from day 3 through 7 completely prevented growth of the secondary tumor. 6-MPG showed no effect on growth of colon 26 adenocarcinoma cells inoculated in place of the secondary MethA cells (antigen specificity). 6-MPG did not inhibit the secondary MethA growth in the BALB/c (nu/nu) mouse. The inhibitory effect of 6-MPG on the secondary tumor growth was diminished by prior treatment of the primed animals with cyclosporin A and anti-Thy antibody. Spleen cells from the tumor-bearing mice treated with 6-MPG showed a tumor-neutralizing activity (Winn assay). Treatment of the spleen cells with anti-CD8 antibody plus complement diminished the tumor-neutralizing effect but that with anti-CD4 antibody plus complement did not, indicating that CD8-positive cells are responsible for potentiation of the tumor immunity. These results suggest that the antitumor effect of 6-MPG against the secondary tumor is elicited by augmenting tumor specific T-cell production.