Figure 1.

Relationship of immunosuppressive CD14⁺HLA-DR^lo/neg monocytes to other myeloid cells and myeloid derived suppressor cells. A diagram of CD marker commonalities between cell types within the myeloid subclass including MDSCs and other cells with similar CD marker expression. (A) MDSCs of both granulocytic and monocytic lineage reside within the CD33⁺ population of cells. (B) Cells not expressing CD33 are considered to be of lymphoid lineage. (C) Cells not expressing CD14 comprise a separate pool of CD33⁺ subtypes. (D) CD14⁺ monocytes typically strongly express CD33, hereafter noted as CD33⁽⁺⁺⁾. (E) CD15⁽⁺⁾/SSC^(hi)/HLA-DR⁽⁻⁾ normal granulocytes and granulocytic MDSCs. (F) CD15⁽⁻⁾/SSC^(lo)/HLA-DR⁽⁻⁾ immature MDSCs. (G) LIN⁽⁻⁾ HLA-DR⁽⁺⁺⁺⁾ dendritic cells or other myeloid cells. Three sub-populations of monocytes are (H) classical monocytes (CD14⁺CD16-) (I) intermediate monocytes (CD14⁺CD16⁺) (J) Non-classical monocytes (CD14^loCD16⁺) (K) Representation of the combined pool of the three monocyte subtypes (L) The CD14⁺HLA-DR^lo/neg cell most typically arises from the classical monocyte pool, but may also be derived from the intermediate and non-classical monocyte pools. The red lines on the cells represent relative HLA-DR expression on the cells. ^*Under some conditions, granulocytes can express CD14 (126).