Sialic acid binding immunoglobulin-type lectin (Siglec) family are inhibitory receptors with diverse roles in the immune system. Siglec family contains 14 members in human and 9 in murine. Differentially expressed on various white blood cells. Here in this review we are focusing on CD22, also known as Sialic Acid-Binding Ig-Like Lectin 2 (Siglec-2). CD22 gene is located on 19q13.12 and is encoding a 140 kD type I transmembrane glycoprotein on the surface of B cells and is part of the immunoglobulin (Ig) superfamily and has been found only on B cells. CD22 has been shown to play a major role in establishing a baseline level of B-cell inhibition, and thus is a critical determinant of homeostasis in humoral immunity.