PATHOLOGY Dipartimento di Patologia Animale, Igiene e Sanita` Pubblica Veterinaria, Sezione di Anatomia Patologica Veterinaria e Patologia Aviare, Facolta` di Medicina Veterinaria, Universita` degli Studi, Milano, Italy Eosinophilic Crystals as a Distinctive Morphologic Feature of a Hyaline Droplet Nephropathy in a Mouse Model of Acute Myelogenous Leukaemia F. Marchesi 1,5 , S. V. Monestiroli 2,3 , M. Capillo 2,3 , A. Gobbi 2,3 , S. Minucci 2,4 , P. G. Pelicci 2,3 and E. Scanziani 1 Addresses of the authors: 1 Dipartimento di Patologia Animale, Igiene e Sanita` Pubblica Veterinaria, Sezione di Anatomia Patologica Veterinaria e Patologia Aviare, Facolta` di Medicina Veterinaria, Via Celoria 10, 20133 Milano, Italy; 2 Department of Experimental Oncology, European Institute of Oncology, Milano, Italy; 3 IFOM, Istituto FIRC di Oncologia Molecolare, Milano, Italy; 4 Dipartimento di Fisiologia e Biochimica Generale, Facolta` di Scienze Biologiche, Universita` degli Studi di Milano, Italy; 5 Corresponding author: E-mail: francesco.marchesi@unimi.it With 2 figures and 2 tables Received for publication: July 25, 2002 Summary Eosinophilic crystals have been described in the upper and lower respiratory tract, gall bladder, intrahepatic bile ducts and glan- dular stomach of different laboratory mice strains. They have been recently identified as chitinase–like (Ym1/Ym2) proteins. Here we describe the occurrence of eosinophilic crystals in the renal tubules of mice with experimentally induced acute myelo- genous leukaemia. Fourteen FVB/N and 29 129Sv mice of both sexes, 8–10 weeks of age, were employed to establish a model of human acute myelogenous leukaemia. Nine mice that developed a widespread acute myelogenous leukaemia revealed the pres- ence of eosinophilic crystals in renal tubules. The presence of eosinophilic crystals in the kidneys was constantly associated with a hyaline droplet nephropathy. Immunohistochemistry showedthatthecrystalsandthehyalinedropletswerecomposed of chitinase-like (Ym1/Ym2) proteins. Furthermore, immuno- reactivity for Ym1/Ym2 proteins was also detected in the crys- tallinematerialstoredinthecytoplasmoflargemacrophage-like cells or in extracellular localization within the leukaemic infil- trates. On the basis of our results we hypothesize that the detection of the Ym1/Ym2 proteins in the urine of mice might represent a feasible indicator of the burden and progression of the leukaemic condition in our murine model. Introduction Elongated eosinophilic crystals have been observed in the lower respiratory tract of laboratory mice (Green, 1942; Yang and Campbell, 1964; Rabstein et al., 1973). They are occasional findings in aged animals and are frequently associated with lung tumours (Green, 1942). They are also described in association with a pulmonary disease named acidophilic macrophage pneumonia, which has been reported in different laboratory mice strains (Murray and Luz, 1990) and identified as the main cause of early death in the immunopathic moth eaten strain (Ward, 1978). Furthermore, the presence of eosinophilic crystals in the lungs of mice has been reported in murine models of Cryptococcus neformans infection (Huffnagle et al., 1998; Feldmesser et al., 2001), in spontaneous Pneumocystis carinii infection in CD40L knockout mice (Schuh et al., 1997) and in transgenic mice overexpressing IL-13 specifically in the lung(Zhuetal.,1999).Asimilaritybetweeneosinophiliccrystals in the lungs of mice and Charcot–Leyden crystals found in humans has been proposed (Huffnagle et al., 1998; Murray and Luz,1990;Zhuetal.,1999).Thepresenceofelongatedorneedle- shaped eosinophilic crystals has been also reported in the gall bladder(YangandCampbell,1964;Rabsteinetal.,1973)andin intrahepatic bile ducts (Rabstein et al., 1973; Lewis, 1984) of mice used in long-term carcinogenicity studies, as well as in cholangitis experimentally induced in different mice strains by intraperitoneal injection of swine serum (Imaoka et al., 1986). The chemical composition of eosinophilic crystals has been debated. Some authors, based on histochemical investigations, suggested they might be composed of proteins and RNA (Yang and Campbell, 1964). Histopathological and biochemical investigations including sequencing of the crystallizing protein and enzymatic assays of eosinophilic crystals in the lungs of mice have been performed. Based on these results, the genesis of the lesion has been attributed to the crystallization of Ym1 (Guo et al., 2000), a member of a family of closely clustered mammalian proteins sharing sequence homologies with chitin- ases of lower organisms (Jin et al., 1998). These proteins are thought to be responsible for defence mechanisms against chitin-bearingorganismsandalsoinvolvedintherecruitmentof eosinophils (Owhashi et al., 2000). Other authors have des- cribed the role of chitinase-like (Ym1/Ym2) proteins in hyal- inosis and crystal formation in lesions of the upper and lower respiratory tract, glandular stomach and bile ducts of 129 and B6 · 129 mice (Ward et al., 2001). Recently, Ym1 has been characterized as a possible member of a novel lectin gene family and activated macrophages (Chang et al., 2001; Sun et al., 2001) and neutrophils (Harbord et al., 2002) are referred as its main U.S. Copyright Clearance Center Code Statement: 0931–184X/2003/5002–0103 $15.00/0 www.blackwell.de/synergy J. Vet. Med. A 50, 103–107 (2003) Ó 2003 Blackwell Verlag, Berlin ISSN 0931–184X