Abstract. CD44 is a ubiquitous surface molecule that exists as a number of isoforms, generated by alternative splicing of 10 "variant" exons. Little is known about the expression and function of the variant isoforms, except that certain isoforms may play a role in cancer metastasis. We produced mAbs against CD44 variant regions encoded by exons 4v, 6v, and 9v, by immunizing mice with a fusion protein spanning variant exons 3v to 10v. A comprehensive analysis of human tissues revealed that CD44 variant isoforms were expressed widely throughout the body, principally by epithelial cells. However there was differential expression of CD44 variant exons by different epithelia. Most epithelia expressed exon 9v, but much fewer expressed 6v or 4v. The regions of epithelia that expressed the highest levels of the variant isoforms were the generative cells, particularly the basal cells of stratified squamous epithelium, and of glandular epithelium. CD44 variant isoforms were also expressed differentially by leukocytes, with CD44-9v expressed at very low levels and CD44-6v and 4v virtually absent. However, CIM4-9v and CD44-6v were the main variants that were transiently upregulated on T cells after mitogenic stimulation and on myelomonocytic cell lines by TNFot and IFN~ treatment. Some epithelial cell lines could preferentially upregulate CIM4-6v upon IFN3, incubation. These results show that CD44 variant isoforms are expressed much more widely than first appreciated, and that expression of the variant isoforms on some cell types can be modulated by particular cytokines.C D44 is a widely expressed cell surface glycoprotein that serves as an adhesion molecule in cell-substrate and cell-cell interactions, including lymphocyte homing, hemopoiesis, cell migration, and metastasis (for reviews see Haynes et al., 1991; Underhill, 1992; Gtinthert, 1993;Lesley et al., 1993). CD44 also has other functions that relate to lymphocyte activation (Haynes et al., 1989) and the binding of certain cytokines to endothelium (Tanaka et al., 1993). CD44 is a proteoglycan with an NH2-terminal region that is structurally related to several hyaluronate binding proteins (Underhill, 1992). CD44 is known to bind hyaluronate and collagen (Carter and Wayner, 1988;Aruffo et al., 1990;Culty et al., 1990;Miyake et al., 1990) and a chondroitin sulfated form of CD44 binds fibronectin (Jalkanen and Jalkanen, 1992). Additional ligands for CD44 may well exist. The numerous functions and molecular interactions of CD44 probably relate to its complex structure. In addition to the "standard" 85-95-kD form (CD44s), severalThe Basel Institute for Immunology was founded and is supported by E Hoffman-La Roche Ltd., Basel, Switzerland.Address all correspondence to Dr. Charles R. Mackay, Leukosite Inc., 800 Huntington Ave., Boston, MA 02115, or Dr. Ursula Giinthert, The Basel Institute for Immunology, Grenzaeherstrasse 487, CH-4005 Basel, Switzerland.larger "variant" isoforms exist (CD44v) t that are generated by alternative splicing of at least 10 exons (Screaton et al....

CD4 ؉ CD25 ؉ regulatory T cells (Tregs) control immune responses to self-and foreign antigens and play a pivotal role in autoimmune diseases, infectious and noninfectious inflammation, and graft rejection. Since recent experimental studies have indicated that Tregs were able to ameliorate graft-versus-host disease (GvHD), we analyzed the number of infiltrating Tregs in the intestinal mucosa as one site of GvH reactivity using immunoenzymatic labeling to enumerate IntroductionDespite the prophylactic use of potent immunosuppressants, severe graft-versus-host disease (GvHD) is-besides infections-the most relevant complication after allogeneic stem cell transplantation. Immunologically, acute GvHD is characterized by an expansion of donor lymphocytes with cytotoxic reactivity against recipient histocompatibility antigens. The resulting clinical picture includes life-threatening destruction of skin, gut, and liver tissue.In acute GvHD, the transferred immune system lacks the capability to gain control over alloreactive T-cell clones. Therefore, the understanding of mechanisms by which an organism controls allo-or autoimmune reactivity is crucial for the development of successful strategies to prevent and/or control GvHD. Recently, these mechanisms have been further elucidated by the description of a distinct CD4 ϩ T-cell population with the capability to confer nonresponsiveness to T cells against autologous and allogeneic antigens. [1][2][3] These suppressor or regulatory T cells were originally described as a lymphocyte subset that prevents autoimmunity caused by neonatal thymectomy in mice 1 and are characterized by the expression of the interleukin-2 (IL-2) receptor ␣-chain (CD25). More recently, FOXP3, which encodes for a forkhead/winged helix transcription factor called Scurfin, has been identified to be a key regulatory gene required for the development and functional activity of regulatory T cells. [4][5][6][7] Tregs are able to suppress CD4 ϩ and CD8 ϩ T-cell responses to auto-and alloantigens in a contactdependent fashion. 8 In animal models, they can prevent graft rejection 2,3,9 and autoimmune diseases, 8,10 and there is also evidence that inappropriate numbers of Tregs may contribute to the development of chronic inflammatory diseases. 11 Consequently, the question has been raised whether Tregs are also capable of suppressing GvHD. Indeed, it has been shown in different murine models that freshly isolated or ex vivo-expanded donor-type CD4 ϩ CD25 ϩ Tregs are able to delay or even prevent GvH reactivity. [12][13][14][15] Consistent with this, the selective depletion of Tregs leads to an increased severity of acute GvHD in vivo. 16 In humans, however, available data are ambiguous. Whereas Clark et al found elevated numbers of CD4 ϩ CD25 high cells in the peripheral blood of patients with chronic GvHD, 17 Miura et al observed a significantly decreased FOXP3 mRNA expression in the peripheral blood of patients suffering from allogeneic or autologous GvHD. 18 Since the presence of Tregs in the peripheral blo...

SummaryVascular cell adhesion molecule 1 (VCAM-1) mediates extravasation of circulating leukocytes into inflamed tissues, and presumably, plays a role in the immigration of cytotoxic effector lymphocytes into tumor metastases. Since metastases are rarely cleared by blood-borne cells from the immune system, we asked whether the tumor may escape host defense by interfering with the mechanism of effector cell extravasation. Here we show that in mice and humans, VCAM-1 expression is repressed on tumor-infiltrating vascular endothelial cells in the lungs. On lung blood vessels distant from the tumor, VCAM-1 is constitutively expressed. When melanoma and endothelioma cells were cultured on either side of a Nucleopore membrane, the expression of VCAM-1 on the endothelioma cells was inhibited and VCAM-1 gene transcription was suppressed. We propose that the downregulation of VCAM-1 is a mechanism by which vascularized melanoma and carcinoma avoid invasion by cytotoxic cells of the immune system.

CD44 is a transmembrane glycoprotein, which can exist in a multitude of isoforms due to alternative splicing of the pre-mRNA. We have generated monoclonal antibodies to several of these variant regions, which are encoded by 10 additional exons in the extracellular part of the molecule. CD44 variant isoforms have been reported to be involved in the malignant progression of rat and human tumours. The precise localization of CD44 variant isoforms in normal developmental and morphogenetic processes is essential for diagnostic studies of human tumorigenesis. Therefore, we have analysed a large number of different human tissues by immunohistochemistry for the expression of CD44 isoforms containing either exons 4v, 6v or 9v. Expression of exon 9v-isoforms was detected in almost all epithelia analysed, with a few exceptions. Exon 6v isoforms are expressed only in squamous and glandular epithelial, e.g. skin epidermis, sweat and sebaceous glands, oesophagus, ducts of the mammary gland, salivary and prostate glands. Detection of exon 4v-encoded isoforms was restricted to the epidermis and the oesophagus. Similar tissue distributions of CD44 variant isoforms were observed in 10-week-old fetal tissues. Since one of the ligands of CD44 is hyaluronic acid (HA), we also analysed the tissue distribution of HA synthetase. HA synthetase was detected in all tissues analysed, showing good correlation with the expression of the standard form of CD44, CD44s.

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