The transmembrane form of TNF-alpha drives autoantibody production in the absence of CD154: studies using MRL/Mp-Fas(lpr) mice.

It is generally accepted that the interaction between CD40 and its ligand (CD154) plays a decisive role in contact-dependent help for T and B cells. In CD154-deficient MRL/Mp-Fas(lpr) (MRL/lpr) mice, however, high titres of IgG2a-type autoantibodies against small nuclear ribonucleoproteins (snRNPs) are observed. We successfully isolated two CD154-deficient MRL/lpr Th1 lines, which could provide B cell help for anti-snRNP antibody production. The proliferative responses of the Th1 cell lines were MHC class II (I-Ek)-restricted. Although syngeneic B cell proliferation was induced by Th1 lines in both a contact-dependent and -independent manner, the soluble form of TNF-alpha (sTNF-alpha) was not involved in contact-independent B cell proliferation. On the other hand, both anti-TNF-alpha and TNF-receptor 2 (TNF-R2, p75) monoclonal antibody (MoAb) blocked contact-dependent B cell proliferation, suggesting that the transmembrane form of TNF-alpha (mTNF-alpha)-TNF-R2 co-stimulation participates in B cell activation. Similarly, anti-TNF-alpha and TNF-R2 MoAb inhibited anti-snRNP antibody production in vitro, but anti-CD154 or TNF-R1 MoAb did not. These results indicate that the interaction of mTNF-alpha on activated Th1 cells with TNF-R2 on B cells may be involved in the autoimmunity seen in MRL mice, and that the blockade of CD40-CD154 co-stimulation may not always be able to suppress some Th1-related manifestations of lupus.