Cell-mediated and innate immunity is important in the clearance of rickettsial infections. CD4+ and CD8+ cells, along with macrophages and dendritic cells, are believed to be sources of inflammatory cytokines such as IFN-γ, TNF-α, Il-1β, and RANTES (CCL5). These cytokines increase production of nitric oxide synthetase and hydrogen peroxide by the endothelial cell, which helps to eliminate the organisms.56,57 The endothelial cells themselves also produce cytokines such as , Il-8, and MCP-1 (CCL2) that recruit immune cells and combat infection. Antibodies are not thought to be important initially for clearance of infection because they form after the fulminant stages of disease.57 However, antibodies are long-lived