HERPESVIRUS SAIMIRI-TRANSFORMED HUMAN CD4(-CELLS CAN PROVIDE POLYCLONAL B-CELL HELP VIA THE CD40 LIGAND AS WELL AS THE TNF-ALPHA PATHWAY AND THROUGH RELEASE OF LYMPHOKINES() T)

We have developed human CD4(+) T cell lines from the PBL of normal don ors by infection with Herpesvirus saimiri (HVS), to evaluate functiona l properties of these immortalized lymphocytes. In this report, we cha racterize two such CD4(+) T cell lines, CHCD4 and MHCD4, which were de rived from two different donors. These cells grew independent of exoge nous IL-2 stimulation for over 1 yr, and expressed surface markers (CD 25(+), CD69(+), HLA-DR(+), and B7(+)) associated with an activated T c ell phenotype. Both lines constitutively produced and released IFN-gam ma, but no IL-2 or IL-4. However, the surface expression of the two ce ll lines differed in that CHCD4 constitutively expressed CD40 ligand ( CD40L) and membrane TNF-alpha, but MHCD4 did not. Also, CHCD4, but not MHCD4, potently induced polyclonal B cell activation and differentiat ion in the absence of PWM, in an MHC-unrestricted fashion. The B cell help afforded by CHCD4 included contact-dependent and soluble componen ts. Contact-dependent help was strongly inhibited by mAb, against CD40 L (5C8) and to a lesser extent, by anti-TNF-alpha Ab. The CD40L-depend ent helper function of CHCD4 contrasts with the recent description of other HVS-transformed CD4(+) T cells that provide B cell help primaril y via the membrane TNF-alpha and TNF-alpha R pathways. Furthermore, CH CD4 cells also secreted soluble factors that could mediate CD40-linked B cell differentiation into Ab-producing cells. interestingly, this f actor is not likely to be IL-2, IL-4, IL-6, IL-10, IL-15, TNF-alpha, o r IFN-gamma as Abs against these cytokines were not able to inhibit th e contact-independent B cell help by CHCD4. These results indicate tha t HVS-immortalization of CD4(+) lymphocytes may produce T cell clones with a spectrum of important contact-dependent, as well as contact-ind ependent, B cell helper function capacities.