TLR9 and infection: To investigate the mechanism of the enhanced response of macrophages to pRBC lysate primed by infection of P. yoelii 17XL or 17XNL, the levels of inflammatory cytokines of TNF and IL-6 released by macrophages stimulated with TLR2 agonist Pam3CSK4, TLR4 agonist LPS, or TLR9 agonist CpG, were measured.