CD48 binds to heparan sulfate on the surface of epithelial cells.

CD48 is a member of the immunoglobulin superfamily whose cell surface expression is strikingly up-regulated on the surface of Epstein-Barr virus-infected B cells. To date, no ligand for human CD48 has been characterized. In this study, we show that human recombinant CD48 binds to the glycosaminoglycan heparan sulfate on the surface of human epithelial cells. We have produced a monoclonal antibody (615) against epithelial cell surfaces that blocks this binding and show that it too recognizes heparan sulfate. The specific epitope on heparan sulfate that is recognized by the antibody and is involved in binding is also expressed in vivo on the basolateral surfaces of mucosal epithelium and lamina propria.

Schistosoma mansoni: genetic restriction and cytokine profile of the CD4 + T helper cell response to dominant epitope peptide of major egg antigen Sm-p40.

Granuloma formation in schistosomiasis is mediated by MHC class II-restricted CD4 + T helper lymphocytes sensitized to egg antigens. We previously reported that C3H mice, which develop large granulomas, display strong CD4 + T helper cell responses to the major egg antigen Sm-p40. Moreover, all members of a panel of egg antigen-specific T cell hybridomas responded to the Sm-p40 antigen. Given the significance of the Sm-p40 molecule in the C3H T cell repertoire against schistosomal egg antigens, the current work was undertaken to map its immunogenic epitopes, using a library of 15 synthetic overlapping 30-mer peptides. The dominant epitope recognized by polyclonal CD4 + Th cells was located in peptide 10 (amino acids 229-258); subdominant epitopes were detected in peptides 8 (amino acids 179-208) and 12 (amino acids 279-308). The anti-Sm-p40 T cell hybridomas variously responded to any one of the same three stimulatory peptides. Furthermore, studies with various mouse strains demonstrated that a strong anti-Sm-p40 response was restricted by H-2(k). Interestingly, the cells responding to peptide 10 and to the Sm-p40 antigen only secreted IL-2 and IFN-gamma, but not IL-4 and IL-10, indicating that they are entirely of the Th-1-type, a subset with demonstrated capacity to mediate egg granuloma formation. The identification of dominant epitopes within key egg antigens offers opportunities for desensitization of the CD4 + Th cells that mediate pathology in schistosomia sis.

Human mucopolysaccharidosis IIID: clinical, biochemical, morphological and immunohistochemical characteristics.

Mucopolysaccharidosis IIID (MPS IIID) is one of the rarest of the MPS-III syndromes. To date, the clinical manifestations of 10 patients have been reported, the deficient N-acetylglucosamine 6-sulfatase (G6S) enzyme has been purified, and the G6S gene has been cloned, sequenced and localized. However, morphological manifestations of this condition have not been reported and the pathogenesis of the severe neurological deficits remains an enigma. In this paper we describe and correlate the clinical, biochemical and pathological observations for 2 cases of MPS IIID. We used monoclonal antibodies against heparan sulfate (HS) and GM2-ganglioside, thin layer chromatography, mass spectrometry, and morphological techniques to demonstrate the nature and the distribution of the uncatabolized substrates. The majority of the cells in various tissues showed morphological changes expected with lysosomal storage of HS. The central nervous system (CNS) was most severely affected because of the secondary storage of GM2 and GM3 gangliosides in addition to the primary accumulation of HS. The extent as well as the distribution of the diverse storage materials varied within and among different neurons as observed in MPS-III A, B, and C syndromes. This study supports the hypothesis that the neurological dysfunction and neurodegeneration common to the Sanfilippo syndromes is, in part, due to the secondary metabolic perturbations induced by HS accumulation.

A ligand for human CD48 on epithelial cells.

CD48 is a member of the Ig superfamily with a high degree of sequence homology to CD58 (LFA-3). In rodents, CD48 is the ligand for CD2 whereas in humans, CD58 is the ligand for CD2. Despite intensive efforts, no ligand for human CD48 has been convincingly demonstrated. We now show that a ligand for human CD48 is present on epithelial cells. The ligand was detected based on the ability of epithelial cells to bind both a decameric, soluble CD48 IgM fusion protein and monomeric CD48 immobilized on plastic dishes. mAbs raised to the ligand completely block binding of CD48 to all epithelial cells tested. We further show that the cell surface proteoglycan CD44 plays an auxiliary role in the binding of epithelial cells to CD48 and that this interaction involves the glycosaminoglycan binding site of CD44. No interaction of human CD48 with CD2 was detected. This is the first clear demonstration that human CD48 can function as an adhesion molecule and suggests a role for CD48 in lymphocyte epithelial cell interactions.

Human cell-adhesion molecule CD2 binds CD58 (LFA-3) with a very low affinity and an extremely fast dissociation rate but does not bind CD48 or CD59.

CD2 is a T lymphocyte cell-adhesion molecule (CAM) belonging to the immunoglobulin superfamily (IgSF) which mediates transient adhesion of T cells to antigen-presenting cells and target cells. Reported ligands for human CD2 include the structurally-related IgSF CAMs CD58 (LFA-3) and CD48 as well as, more controversially, the unrelated cell-surface glycoprotein CD59. Using surface plasmon resonance technology, which avoids several pitfalls of conventional binding assays, we recently reported that rat CD2 binds rat CD48 with a very low affinity (Kd 60-90 microM) and dissociates rapidly (koff > or = 6 s-1) [van der Merwe, P. A., Brown, M. H., Davis, S. J., & Barclay, A. N. (1993) EMBO J. 12, 4945-4954]. In contrast, a study using conventional equilibrium binding methods reported a much higher affinity (Kd 0.4 microM) for human CD2 binding CD58 which suggested that the weak binding of rat CD2 to CD48 may not represent a typical CAM interaction. In the present study we have used surface plasmon resonance to obtain definitive affinity and kinetic data on the interactions of a soluble, recombinant form of human CD2 with soluble forms of CD58, CD48, and CD59. Binding of CD2 to CD58 was readily detected but we were unable to detect any direct interaction between CD2 and either CD59 or CD48 under conditions in which very low affinity interactions (Kd approximately 0.5 mM) would have been detected. In contrast to previous reports we found that human CD2 bound CD58 with a very low affinity (Kd 9-22 microM) and dissociated with an extremely fast dissociation rate constant (koff > or = 4 s-1). The association rate constant (kon) could not be measured directly but was calculated to be > or = 400,000 M-1s-1. Taken together, these results provide conclusive evidence that CAM interactions can have very low affinities and extremely fast dissociation rate constants.

Strong priming of T cells adoptively transferred into scid mice.

We have examined the requirements for activating unprimed T cells in vivo by transferring T cells into scid mice, which lack mature B and T cells. Purified adult thymocytes and a protein antigen, keyhole limpet hemocyanin (KLH), were injected into scid mice. scid mice injected with T cells and KLH developed cellular lymph nodes containing CD4+ and CD8+ T cells. Cells recovered from the lymph nodes of injected scid mice proliferated and secreted interleukin 2 in response to KLH in vitro. The results indicate that T cells can be primed to KLH in the scid mouse in the absence of B cells.