Up-regulation of major histocompatibility complexes (e.g., HLA-DR) and co-receptors (e.g., CD86 and CD40) required for activation of T cells and secretion of soluble mediators to mobilize antibacterial functions in other cells and tissues, recruit immune cells, and promote bactericidal reactive oxygen species (ROS) production are key features of the innate immune response to bacterial infection. This evidence concerns the gene CD40 and bacterial infectious disease.