A substantial body of evidence demonstrates that opiates and opioid peptides modulate immune function. The present study used highly purified murine CD4+ and CD8+ T-cells to determine the effects of delta opioid receptor (DOR) agonists on proliferation. Splenic T-cells, obtained from male or female C57BL/6 or CD1 mice, were separated by a fluorescence activated cell sorter. Cells were stimulated to proliferate in serum free medium by cross-linking the T-cell receptor using plate-coated anti-CD3-epsilon, 3H-thymidine uptake was determined at 48 hours. Previous experiments had shown that deltorphin and [D-Ala2]-met-enkephalinamide (DAME), at concentrations from 10(-11) to 10(-7) M, dose dependently inhibited the proliferation of CD4+ and CD8+ T-cells obtained from female C57BL/6 or CD1 mice. Similarly, the experiments herein demonstrate that proliferation of CD4+ T-cells from female CD1 mice was inhibited by 2,5 DPDP-enkephalin (DPDP-E), in direct relation to dose. In contrast, the anti-proliferative response of cells from C57BL/6 mice demonstrated an inverse relationship to dose. At 10(-11) M, the most effective dose of DPDP-E studied, 3H-thymidine uptake was inhibited by 50%. The selective DOR antagonist, naltrindole (10(-12) M), abolished this. DAME was used to compare the effects of DOR agonists on CD8+ T-cells from both strains of female mice. 3H-Thymidine uptake was dose-dependently inhibited to a similar degree in both strains; 10(-7) M DAME maximally reduced proliferation by 70%. DAME had similar effects on both CD8+ and CD4+ T-cells from male mice, and its inhibitory effect was markedly attenuated after 72 hours.(ABSTRACT TRUNCATED AT 250 WORDS)