Blockade of CD40-CD154 interferes with human T cell engraftment in scid mice.

Antibodies to the ligand for CD40 (CD154) have been shown to exert profound effects on the development of cell-mediated immune responses in mice. The present study shows that an antibody to human CD154 (hCD40L) inhibits in vivo Tetanus toxoid (TT) specific secondary antibody responses in hu-PBL-scid mice, as well as the expansion of xenoreactive human T cells in the scid mice. A possible cause for the reduced expansion of xenoreactive, human T cells, was the decreased expression of murine B7.1 and B7.2 caused by the administration of anti-hCD40L. Therefore, it may be that defective maturation of murine antigen-presenting cells impeded the priming and expansion of human xenoreactive T cells.

Bidirectional regulation of human B cell responses by CD40-CD40 ligand interactions.

Positive and negative effects of CD40 ligation on human B cell function were suggested by the observation that mAb to CD40 ligand partially blocked the suppressive influences of anti-CD3-stimulated control CD4+ T cells, as well as the B cell stimulatory effects of anti-CD3 activated mitomycin C-treated CD4+ T cells. To examine the negative effects of CD40 ligation in greater detail, B cells were cultured with anti-CD3 activated mitomycin C-treated CD4+ T cells that expressed optimal levels of CD40 ligand; additional recombinant human CD40 ligand significantly suppressed Ig production, but not proliferation. In contrast, when B cells were stimulated with SAC (formalinized Cowan I strain Staphylococcus aureus) and IL-2 in the absence of T cells, small amounts of recombinant CD40 ligand-stimulated Ig production, whereas larger quantities directly suppressed Ig secretion. The suppressive action of CD40 ligation on Ig production was most apparent after initial B cell activation. Moreover, IgD-memory B cells were significantly more sensitive to inhibition by CD40 ligation than IgD+ naive B cells. Engagement of CD40 not only suppressed Ig secretion by IgD- memory B cells, but also expression of CD38. Finally, activated B cells acquired the capacity to down-regulate CD40 ligand expression by stimulated CD4+ T cells more effectively than resting B cells. These results indicate that during T cell-B cell collaboration, engagement of CD40 can influence Ig production both positively and negatively, depending on the density of CD40 ligand as well as the stage of B cell activation and differentiation.

Analysis of CD40-CD40 ligand interactions in the regulation of human B cell function.

CD40-CD40 ligand interactions play an essential role in T cell/B cell collaboration. The data presented in this review have served to widen the scope of CD40-CD40 ligand interactions to include initial activation, proliferation, differentiation, and isotype switching of B cells, as well as subsequent downregulation of B cell function. Moreover, CD40 ligand expression by activated B cells is likely to play an essential role in facilitating ongoing responses of stimulated B cells maturing in germinal centers. Finally, CD40 expression by activated T cells may also play an important role in regulating the function of helper T cells within germinal centers. In summary, emerging data have expanded the role of CD40-CD40 ligand interaction during T cell/B cell collaboration and have emphasized its potential to regulate many of the functions of both partners in this essential interaction involved in antibody production.

Assessment of a positive selection technique using an avidin column to isolate human peripheral blood T cell subsets.

The current studies were designed to assess a new technique for positively selecting human T cells from whole peripheral blood mononuclear cells using the minimal amount of monoclonal antibody required to bind the T cell to an avidin column indirectly via a biotin-conjugated secondary antibody. Positive selection of T cells has previously been avoided because the saturating amounts of antibodies required for other isolation procedures can lead to aberrant results in assays of T cell activation and function. The avidin column technique for obtaining purified T cell subsets was compared to a multi-step procedure that included negative selection panning. The positive selection technique was easily performed within 4 h whereas the negative selection technique required a minimum of 12 h to complete. The avidin column technique proved to be a rapid and simple method for isolating T cell subsets of high purity and normal functional capabilities. Since minimal amounts of monoclonal antibodies were used for the purification protocol, no consistent inhibitory or stimulatory effect of the residual antibody was noted in assays of activation and proliferation of positively selected T cells compared to T cells isolated by negative selection panning.

Rheumatoid synovium is enriched in CD45RBdim mature memory T cells that are potent helpers for B cell differentiation.

OBJECTIVE: To delineate the phenotype and function of synovial T cells in rheumatoid arthritis (RA). METHODS: T cells from normal subjects or from RA peripheral blood (PB), synovial fluid (SF), or synovial tissue (ST) were analyzed phenotypically and functionally. RESULTS: RA SF and ST T cells were found to be markedly enriched in CD45RAdim, CD45RO+, CD45RBdim mature memory cells, whereas in the PB, CD45RAbright naive T cells were more frequent than CD45RO+ memory T cells, and only a minority were CD45RBdim. SF and ST T cells proliferated less well and produced less interleukin-2 in response to mitogenic stimuli than did PB T cells. However, synovial T cells effectively promoted the production of Ig from normal B cells. Moreover, PB and synovial T cells differed in their capacity to down-regulate immunoglobulin production. Anti-CD3-stimulated PB T cells suppressed Ig production unless their proliferation was prevented with mitomycin C. In contrast, synovial T cells were potent helpers of B cell Ig production regardless of antecedent treatment with mitomycin C. To examine the relationship between the CD45RBdim phenotype and B cell help, CD45RBdim T cells were sorted from PB. As opposed to the findings with synovial T cells, suppression by control PB CD45RBdim T cells was observed, but only when large numbers were employed. B cell Ig production was enhanced after treatment of PB CD45RBdim T cells with mitomycin C. In contrast, healthy control sorted CD45RBbright or sorted CD4+, CD45RO+, CD45RBbright T cells did not support Ig secretion. After treatment with mitomycin C, both of these populations were more effective helpers of Ig production. CONCLUSION: RA synovium is enriched in differentiated CD45RBdim memory T cells with potent helper activity and diminished capacity to down-regulate B cells, strongly implying an active role for these cells in the production of Ig in the synovium, and thus in the propagation of disease.