The beta-2 integrin chain gene is designated ITGB2 and the leukocyte antigen has been designated CD18. The 3 alpha integrin chains associated individually with the beta-2 chain as a heterodimer have gene designations of ITGAL, ITGAM, and ITGAX, and leukocyte antigen designations of CD11A, CD11B, and CD11C, respectively.The expression of CD18 was increased in lymphoblastoid cells from persons with Down syndrome, consistent with the location of the gene on chromosome 21.The ITGB2 gene spans approximately 40 kb and contains 16 exons and all exon/intron boundaries conform to the GT/AG splicing consensus. Furthermore,ITGB2 was constitutively clustered. Although it was expressed on the cell surface at normal levels and was capable of function following extracellular stimulation, it could not be activated via the “inside-out” signaling pathways.