In 21 patients with lymphoproliferative disease of granular lymphocytes (LDGL), we investigated the expression and the function of molecules belonging to TNF-receptor and TNF-ligand superfamilies (CD30/CD30L; CD40/CD40L; CD27/CD70; Fas [CD95]/FasL[CD95L]). Fourteen patients were characterized by a proliferation of granular lymphocytes (GLs) expressing the CD3(+)CD16(+) phenotype, whereas 7 cases showed the CD3(-)CD16(+) CD56 +/- phenotype. Our data show that both CD3(+) and CD3-GLs are preferentially equipped with CD30, CD40, CD40L, CD70, and CD95 antigens; this pattern is usually associated with the lack of CD27 and CD30L antigens expression. CD95L was demonstrated in the cytoplasm in 14 of 21 cases by flow cytometry, but a definite signal was demonstrated in all cases studied using polymerase chain reaction analysis. On functional grounds, a stimulatory activity on rIL-2 mediated redirected-cytotoxicity against Fcgamma+ P815 targets was demonstrated with anti-CD30, CD40, CD40L, CD70, CD95, and CD95L mAbs, although resting cells were unable to exhibit significant redirected-cell lysis. The addition of anti-CD30, CD30L, CD40, CD40L, CD95, and CD95L mAbs did not show any significant effect on cell proliferation at resting conditions or after rIL-2 stimulation, whereas anti-CD70 mAb mediated cell proliferation in 6 of 10 cases tested. This figure was not related to an increase in apoptotic cells, as investigated by Annexin-V expression. Our data indicate that both CD3(+) and CD3(-) GLs are equipped with different costimulatory antigens, supporting the concept that these cells are in vivo activated and suggesting that these molecules might play a role in the cytotoxic mechanisms of GLs. (Blood. 2000;96:647-654)