TNF and infection: Additionally, although expansion of the BM LSK population is a hallmark of infections induced by various pathogens including bacteria, fungi, and viruses (5, 9, 42–47), it is well-documented that Sca-1, a canonical stem cell marker, can be upregulated on hematopoietic cells including non-HSCs during inflammation by either IFNs or TNFα (10, 48–50).