IN VIVO INHIBITION OF CONCANAVALIN A-INDUCED SUPPRESSOR T CELLS BY 5-FLUOROURACIL

Spleen cells of mice inoculated intravenously (iv) with concanavalin A (Con A) suppressed the in vitro normal spleen cell blastogenesis. The suppressor cells, as determined by measuring the inhibition of in vitro T cell blastogenesis by Con A, were resistant to X-irradiation. They lacked surface Ig and were abrogated by treatment with αThy 1.2 antibody and complement, but not with complement alone, indicating that these suppressor cells are not B cells but T cells. Inoculation of 5-fluorouracil (5-FU) inhibited the induction and/or activity of these suppressor cells, whereas that of cyclophosphamide (CY), adriamycin, vincristine, or 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitrosourea (ACNU) did not at any interval tested. Since two other antimetabolic agents, 6-mercaptopurine and 2'-deoxyguanosine, were also effective in inhibiting these suppressor T cells, it was supposed that Con A-induced suppressor T cells are metabolically more active than the other T subpopulations. The findings that CY and ACNU decreased the number of T cells as much as or more than 5-FU did, but that they did not inhibit these suppressor T cells, suggests that 5-FU more or less selectively inhibited this suppressor T-cell subpopulation.