MDSCs are broadly classified into two main subtypes: monocytic MDSCs (M-MDSCs) and granulocytic or polymorphonuclear MDSCs (PMN-MDSCs). M-MDSCs resemble monocytes and are characterized by the expression of markers such as CD14 and CD33, while PMN-MDSCs resemble neutrophils and are characterized by the expression of CD15 and CD11b. Both subtypes play significant roles in immunosuppression but may differ in their mechanisms of action and the cytokines they produce.
