Comparisons of CD11 amino acid sequences. CD18 pairs with CD11b, CD11a, CD11c, and CD11d, and together, these make up the β2 integrin family. The four CD11 protein sequences (encoded by ITGAM, ITGAX, ITGAD, and ITGAL) were aligned by using MutAlin. The numbers indicate the CD11b codons, and all other sequences are aligned relative to this. F941 and G1145 of CD11b are indicated by arrows. The phenylalanine at codon 941 is present across all four CD11 polypeptides; the glycine at codon 1145 is not found in any other CD11 polypeptide.