ABSTRACT

Introduction ai-Microglobulin (aim ) was discovered in human urine 40 years ago and was named in the

tradidon of plasma proteins, reflecting its small size (26 kDa) and its electrophoretic migration slightly behind albumin.1 The protein was characterized by several research groups and given the alternative names protein HC, “human complex-forming protein, heterogeneous in charge”2 and ai-microglycoprotein.3 aiM , retinol-binding protein (RBP) and β-lactoglobulin were the three original members when the lipocalin family was defined in 1985.4

The physiological role of aim has only recently been clarified. Immunoregulatory (mainly suppressive) properties o f a im were identified (see below), but did not seem distinct or strong enough to constitute the major function of the molecule in vivo. However, several very recent reports have suggested that a im may play a biological role as an anti-oxidant with oxidant-scavenging and enzymatic reductase properties. In this review, we will describe the structural features of aim , its distribution among tissues and species and the anti-oxidation and immunoregulatory properties o f this lipocalin.