For instance, purified common lymphoid progenitors (CLPs) from HSV-1-infected mice are biased toward DC differentiation in ex vivo cultures [23]. Similarly, CLPs from mice treated with the TLR9 ligand CpG oligodeoxynucleotide (ODN) beta-catenin pathway have a limited ability to generate B-lineage cells, but an augmented competence to generate DCs [23]. Infection studies using TLR-deficient mice have perhaps not surprisingly revealed defects in HSPC mobilization and emergency myelopoiesis. CLPs from TLR-deficient mice, for example, are not primed to become

DCs during HSV-1 infection [23]. Similarly, vaccinia virus infection induces an increase in LKS+ cell numbers, with an associated decrease in common myeloid progenitors (CMPs) and an increase in the number of later stage myeloid precursors and differentiated myeloid cells; these responses

all require MyD88 [24]. Mycobacterial infection also triggers TLR2/MyD88-dependent amplification of the LKS+ population, as well as granulocyte–monocyte progenitors (GMPs), in a murine model [25]. Moreover, we have shown that the BM LKS+ cell population expands rapidly following Candida albicans fungemia in a TLR2-dependent manner [26]. In contrast, Scumpia et al. [27] described that this expansion following bacterial infection occurs in the absence of TLR signaling, although the interpretation of the in vivo results is difficult Quizartinib supplier as MyD88−/− mice are more susceptible to most infections; therefore, possible differences between control and knockout mice during infection may be masked by different tissue invasion by the microorganism. It should be noted that most findings on the expansion of specific cell types, such as LKS positivity following infection, are based on phenotypic characterization, and the phenotype does not necessarily correlate with functionality of HSPCs as stem cells markers are likely to

be affected by infection. For instance, lineage-restricted progenitors, which are normally Sca-1−, have been reported to upregulate Sca-1 expression upon infection and/or inflammation and are then found within the LKS+ fraction, with the consequent reduction of the myeloid progenitor fraction. Therefore, it is important to validate the HSC status postinfection by using multiple phenotypic Etomidate criteria as well as functional studies [5, 28]. TLR-dependent alterations in hematopoiesis during infection could be explained in at least two ways: (i) HSPC expansion could be an indirect effect of cytokines or growth factors produced by differentiated hematopoietic or nonhematopoietic cells detecting microbes, or (ii) microbes or microbial components might directly induce HSPC proliferation. These possibilities are not mutually exclusive, and both could involve TLR-mediated recognition of microbes or microbe-derived ligands. PRR expression by HSPCs and a role for PRRs in emergency myelopoiesis were first reported in 2006. Nagai et al.