MATERIALS AND METHODS

Mice. Inbred CBA/J, SJL/J, C57BL/6 (66). BALB/c nude, and hybrid (66 x DBA/2) FI (EDPF,).(SJL/J x CBA/J) FI and (BALB/c x DBA/P) F,(CD2F1) mice were obtained from the Mammalian Genetics Section, National Cancer Institute, Bethesda, MD. lymphoma of A/Sn origin (61, was maintained as stationary suspension Tumors. YAC-1, a tissue culture cell line of YAC, a Moloney-induced culture in RPMl 1640 medium supplemented with 20% fetal calf serum. Drugs. Pyran copolymer (NSC 4601 5) was obtained from the Hercules Research Center (Wilmington, DE). Pyran was dissolved in sterile 0.9% NaCl solution and the pH was adjusted to 7.0 by using 1.0 N NaOH. 1-Carrageenan was obtained from Marine Colloids Inc.(Rockland, Me.), Carrageenan was dissolved in saline in a boiling water bath and injected iv into mice. CY and 2'-deoxy-5-fluorouridine (FUdR) were obtained from the Sigma Chemical Co.(St. Louis, MO).'251-labeled 2" deoxyuridine ('Z51UdR)(specific activity, 8 to 10 mCi/mg) was purchased from the Radiochemical Centre (Amersham, Buckinghamshire. England). Cy, FUdR. and'251UdR were dissolved in 0.85% NaCl solution. Cell fractionation. Nylon column: spleen cells were passed over a nylon fiber column as previously described (7). Treatment with carbonyl iron end