Cluster of differentiation molecule 11b (CD11b)/Integrin alpha M (ITGAM) is a transmembrane protein forming heterodimers that are composed of ? and ? subunits. CD11b is expressed by, and commonly used as a marker for, myeloid lineage cells, including neutrophils, monocytes, macrophages, and microglia. CD11b is phosphorylated at Ser1126 (cytoplasmic tail) in neutrophils. Research has shown that this phosphorylation event plays a role for leukocytes traveling from the blood stream to tissues. Furthermore, genome-wide association studies have linked CD11b to autoimmune diseases, such as systemic lupus erythematous (SLE).