Herpesvirus saimiri-transformed human CD4+ T cells can provide polyclonal B cell help via the CD40 ligand as well as the TNF-alpha pathway and through release of lymphokines.

We have developed human CD4+ T cell lines from the PBL of normal donors by infection with Herpesvirus saimiri (HVS), to evaluate functional properties of these immortalized lymphocytes. In this report, we characterize two such CD4+ T cell lines, CHCD4 and MHCD4, which were derived from two different donors. These cells grew independent of exogenous IL-2 stimulation for over 1 yr, and expressed surface markers (CD25+, CD69+, HLA-DR+, and B7+) associated with an activated T cell phenotype. Both lines constitutively produced and released IFN-gamma, but no IL-2 or IL-4. However, the surface expression of the two cell 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 differentiation in the absence of PWM, in an MHC-unrestricted fashion. The B cell help afforded by CHCD4 included contact-dependent and soluble components. Contact-dependent help was strongly inhibited by mAb against CD40L (5C8) and to a lesser extent, by anti-TNF-alpha Ab. The CD40L-dependent helper function of CHCD4 contrasts with the recent description of other HVS-transformed CD4+ T cells that provide B cell help primarily via the membrane TNF-alpha and TNF-alphaR pathways. Furthermore, CHCD4 cells also secreted soluble factors that could mediate CD40-linked B cell differentiation into Ab-producing cells. Interestingly, this factor is not likely to be IL-2, IL-4, IL-6, IL-10, IL-15, TNF-alpha, or IFN-gamma as Abs against these cytokines were not able to inhibit the contact-independent B cell help by CHCD4. These results indicate that HVS-immortalization of CD4+ lymphocytes may produce T cell clones with a spectrum of important contact-dependent, as well as contact-independent, B cell helper function capacities.