Within this context, we concluded (i) that loads of B. abortus in the BM remain constant and are long lasting; (ii) that B. abortus-infected BM displays histopathological modifications associated with augmented numbers of multipotent progenitor and active hematopoietic stem cells, PMNs, and CD4+ lymphocytes during the acute phase of the infection; and (iii) that the three types of infected cells in the BM are monocytes, PMNs, and GMP cells. Here, CD4 is linked to infection.