During screening of a murine macrophage cDNA repertoire for factors potentially able to modulate glomerular cell responses to injury, we identified a gene coding for the murine protein 24p3 lipocalin. Immunostaining of normal rat kidney sections showed positive 24p3-like staining in distal tubules/collecting ducts and small muscular arteries. Although most glomeruli were negative, some did exhibit small numbers of positively stained cells. Cultured rat glomeruli and glomerular mesangial cells secreted the 24p3-like protein in response to macrophage-conditioned medium (MPCM) and the cytokine IL-1beta. MPCM derived from TGFbeta-pretreated macrophages enhanced mesangial cell 24p3 secretion. In contrast, addition of anti-IL-1beta neutralising antibody to MPCM or IL-1beta resulted in suppression of 24p3 secretion. Co-culture of mesangial cells with varying numbers of non-LPS-treated macrophages resulted in dose-dependent secretion of 24p3 into culture supernatants. Archival sections from polyvinyl alcohol-treated and cholesterol-fed rats showed positive glomerular staining for 24p3 in and around glomerular foam cells. Nucleotide sequencing of rat mesangial cell-derived 24p3 cDNA revealed it to be identical to rat alpha-2-microglobulin-related protein (alpha2microGRP), the rat homologue of murine 24p3. These data provide the first description of rat alpha2microGRP in the context of mesangial cell pathophysiology.