TLR4 enhances clonal expansion of CD4+ T cells

Microbial adjuvants are essential for the development of T cell-dependent antibody production, recall T cell proliferation and IFN-g production following immunization with protein antigens. Objective: Determine that clonal expansion of naïve CD4 T cells depends on efficient costimulation when antigen-presenting cells encounter lipopolysaccharide. Methods: 5 x 10^6 pooled mesenteric and peripheral lymph node and spleen T cells from FliC-specific TCR transgenic SM1 CD90.1+ congenic mice were stained with a vital dye, 5-(and-6)-carboxyfluorescein diacetate succinimidyl ester (CFSE) and inoculated intravenously into C57BL/6, C57BL/10, or C57BL/10ScCr (Toll-like receptor 4-deficient) mice. Ten to 100 mg of FliC 427-441 peptide with or without 25-50 mg of E. coli J5 LPS was injected i.v. into each recipient mouse. Spleen cells were harvested 5 days later, permeabilized and stained with fluorochrome-labeled anti-CD4, anti-CD90.1 and anti-IL-2 mAbs. Using flow cytometry, we measured FliC-specific T cell clonal expansion by virtue of CFSE dilution and IL-2 production within transferred T cells. Detection of APC activation was achieved with anti-CD11c or anti-CD11b mAb and anti-CD86, anti-IL-1 and anti-IL-12 mAb. Results: The adjuvant lipopolysaccharide enhanced IL-2 production and clonal expansion by antigen-specific CD4 T cells, CD80/CD86 expression, and IL-1 and IL-12 production by antigen-presenting cells. All of these effects were dependent on Toll-like receptor 4 expression by cells other than the antigen-specific CD4 T cells. Conclusions: The ability of lipopolysaccharide to increase the number of antigen-specific CD4 T cells that survive after immunization likely explains the previous finding that antigen-specific proliferation by T cells from normal mice depends on prior exposure to antigen and adjuvant.