CD40 ligand expression in Mycobacterium bovis BCG infection and its regulation by cytokines: A direct role of interleukin 12

Background. Activation and clonal expansion of T cells require not only the recognition of processed antigen on the surface of the antigen presenting cell (APC) by T-cell receptor (TCR), but also involve co-stimulatory signal s that are provided by the simultaneous engagement of cell surface molecule s expressed by both the APC and the T cell. Interaction between CD40 and it s ligand (CD40 (L) over bar) is known to mediate host immune response and T -cell-mediated effector functions in mycobacterial infections in mice. Tn t his work, we investigated the capacity of Mycobacterium bovis (M, bovis) BC G to induce the expression of CD CD40L on human T cells. Methods. Human cells were obtained from healthy adults by centrifugation us ing Ficoll/Hypaque. Cells (1 X 10(6)) were incubated in RPMI medium with BC G. After incubation at 37 degreesC in 5% CO2 atmosphere for 40 h, cells wer e collected and double-stained with anti-CD40L-PE and anti-CD4-FITC or anti -CD8-FITC mAb. The quantification of positively stained population was base d on samples stained with isotype control antibodies analyzed on a fACScan. Results. M, bovis BCG stimulation induced a significant amount of CD40L exp ression on CD4+ T cells, while CD I OL was not significantly detected on hu man CD8+ T cells. The highest CD40L expression on BCG activated T cells in synergism with interleukin-12 endogenous occurred after a 40-h cell culture with a dose of 10 mug/mL of BCG (84.86 +/- 11.77; mean +/- standard deviat ion [SD]). This CD40L expression on BCG-activated human T cells was signifi cantly inhibited by anti-IL-12 mAb (5.08 +/- 1.7; mean +/- SD). In contrast , anti-IFN-gamma and anti-IL-2 mAb did not have an important role in this e xpression. Conclusions. These results indicate that the capacity of BCG to induce CD40 L expression on human cells represents a novel mechanism underlying the reg ulation of cellular responses against tuberculosis. Furthermore, the result s showed a direct role of IL-12 to enhance the expression of CD40L on BCG-a ctivated human cells. (C) 2001 IMSS. Published by Elsevier Science Inc.