EPO and infection: We found that infection with viral and bacterial pathogens as well as Toll-like receptor 9 (TLR9) ligation with CpG-oligodeoxynucleotide (CpG-ODN) expanded an erythropoietin (EPO)-dependent TER119+CD11a+ cell population in the spleen that had the capacity to differentiate into TER119+CD11chigh and TER119−CD11chigh cells both in vitro and in vivo.