The antigen dose determines T helper subset development by regulation of CD40 ligand

Although the amount of antigen and the strength of T cell stimulation have been suggested to regulate Th1 vs. Th2 polarization, it remains unclear how the antigen dose and the strength of signal is detected by the T cell and translated into differential cytokine production. Using cc-cultures of dend ritic cells (DC) and ovalbumin (OVA)-specific CD4(+) T cells obtained from RAG-2(-/-) DO11.10 mice, we show here that high-dose antigen induced Th1 de velopment by up-regulation of CD40 ligand (CD40L), whereas low-dose antigen stimulation failed to induce CD40L and promoted Th2 development. CD40-CD40 L interaction was essential for IL-12 production by DC. In the absence, de novo IL-4 production by T cells and autocrine Th2 development was induced. Furthermore, our results demonstrate that LFA-1/ICAM interaction promotes T h1 differentiation by lowering the antigen dose required for CD40L up-regul ation. Thus, we propose that (1) peptide-MHC density and (2) accessory mole cules such as LFA-I determine T helper polarization by regulation of CD40L.