Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Regulated expression and neural functions of human natural killer-1 (HNK-1) carbohydrate

Human natural killer-1 (HNK-1) carbohydrate, comprising a unique trisaccharide HSO(3)-3GlcAβ1-3Galβ1-4GlcNAc, shows well-regulated expression and unique functions in the nervous system. Recent studies have revealed sophisticated and complicated expression mechanisms for HNK-1 glycan. Activities of biosynthetic enzymes are controlled through the formation of enzyme-complexes and regulation of subcellular localization. Functional aspects of HNK-1 carbohydrate were examined by overexpression, knockdown, and knockout studies of these enzymes. HNK-1 is involved in several neural functions such as synaptic plasticity, learning and memory, and the underlying molecular mechanisms have been illustrated upon identification of the target carrier glycoproteins of HNK-1 such as the glutamate receptor subunit GluA2 or tenascin-R. In this review, we describe recent findings about HNK-1 carbohydrate that provide further insights into the mechanism of its expression and function in the nervous system.

Differential association of programmed death-1 and CD57 with ex vivo survival of CD8+ T cells in HIV infection

Recent studies have revealed the critical role of programmed death-1 (PD-1) in exhaustion of HIV- and SIV-specific CD8(+) T cells. In this study, we show that high expression of PD-1 correlates with increased ex vivo spontaneous and CD95/Fas-induced apoptosis, particularly in the "effector-memory" CD8(+) T cell population from HIV(+) donors. High expression of PD-1 was linked to a proapoptotic phenotype characterized by low expression of Bcl-2 and IL7-R alpha, high expression of CD95/Fas and high mitochondrial mass. Expression of PD-1 and CD57 was differentially associated with the maturation status of CD8(+) T cells in HIV infection. CD57 was linked to higher apoptosis resistance, with cells expressing a PD-1(L)CD57(H) phenotype exhibiting lower levels of cell death. The majority of HIV-specific CD8(+) T cells were found to express a PD-1(H)CD57(L) or PD-1(H)CD57(H) phenotype. No correlation was found between PD-1 expression and ex vivo polyfunctionality of either HIV- or CMV-specific CD8(+) T cells. Contrary to CD57, high expression of PD-1 was characterized by translocation of PD-1 into the area of CD95/Fas-capping, an early necessary step of CD95/Fas-induced apoptosis. Thus, our data further support the role of PD-1 as a preapoptotic factor for CD8(+) T cells in HIV infection.

Carbohydrate mimics promote functional recovery after peripheral nerve repair

OBJECTIVE

The outcome of peripheral nerve repair is often unsatisfactory, and efficient therapies are not available. We tested the therapeutic potential of functional mimics of the human natural killer cell glycan (3-sulfoglucuronyl beta1-3 galactoside) (HNK-1) epitope, a carbohydrate indicated to favor specificity of motor reinnervation in mice.

METHODS

We applied a linear HNK-1 mimic peptide, scrambled peptide, or vehicle substances in polyethylene cuffs used to reconstruct the severed femoral nerves of adult mice. We used video-based motion analysis and morphological and tracing techniques to monitor the outcome of nerve repair.

RESULTS

After glycomimetic application, quadriceps muscle function recovered to 93% of normal within 3 months. Restoration of function was less complete (71-76%) in control groups. Better functional recovery was associated with larger motoneuron somata, better axonal myelination in the quadriceps nerve, and enhanced precision of target reinnervation. Lesion-induced death of motoneurons was reduced by 20 to 25%. The glycomimetic enhanced survival and neurite outgrowth of both mouse and human motoneurons in vitro by 30 to 75%. Application of a novel cyclic glycomimetic also enhanced functional recovery in vivo.

INTERPRETATION

The improved outcome of nerve repair after glycomimetic application may be attributed to neurotrophic effects. Our results hold promise for therapeutic use in humans.

Follicular B helper T cell activity is confined to CXCR5(hi)ICOS(hi) CD4 T cells and is independent of CD57 expression

The generation of high-affinity antibody-secreting plasma cells critically depends on the presence of CD4 T cells during the germinal center (GC) reaction. GC T cells are so far incompletely characterized in terms of phenotype and function. Here, we show that human follicular B helper T (T(FH)) cells are characterized by high expression of the homeostatic chemokine receptor CXCR5 and the costimulatory molecule ICOS, but not CD57 expression. CXCR5(hi)ICOS(hi) CD4 T cells are the most potent inducers of IgG production that also secrete large amounts of the B cell-attracting chemokine CXCL13. CXCR5(hi)ICOS(hi) CD4 T cells differ from other tonsillar CD4 T cell subsets in their stimulatory activity, proliferative capacity and susceptibility to apoptosis. Large-scale gene expression analysis revealed that T(FH) cells are only distantly related to CXCR5(-) and CXCR5(+) central memory T (T(CM)) as well as effector memory T (T(EM)) cells present in the periphery. CXCR5(hi)ICOS(hi) CD4 T cells appear to be terminally differentiated T helper cells that express a unique set of transcription factors related to the Notch signaling pathway and thus differentiate independent of other T helper cell populations.

Expression of killer cell lectin-like receptor G1 on antigen-specific human CD8+ T lymphocytes during active, latent, and resolved infection and its relation with CD57

Killer cell lectin-like receptor G1 (KLRG1) is one of several inhibitory killer cell lectin-like receptors expressed by NK cells and T lymphocytes, mainly CD8(+) effector/memory cells that can secrete cytokines but have poor proliferative capacity. Using multiparameter flow cytometry, we studied KLRG1 expression on CD8(+) T cells specific for epitopes of CMV, EBV, influenza, and HIV. Over 92% of CD8(+) cells specific for CMV or EBV expressed KLRG1 during the latent stage of these chronic infections. CD8(+) T cell cells specific for HIV epitopes were mostly (72-89%) KLRG1(+), even though not quite at the level of predominance noted with CMV or EBV. Lower frequency of KLRG1 expression was observed among CD8(+) cells specific for influenza (40-73%), a resolved infection without a latent stage. We further observed that CD8(+) cells expressing CD57, a marker of replicative senescence, also expressed KLRG1; however, a population of CD57(-)KLRG1(+) cells was also identified. This population may represent a "memory" phenotype, because they also expressed CD27, CD28, CCR7, and CD127. In contrast, CD57(+)KLRG1(+) cells did not express CD27, CD28, and CCR7, and expressed CD127 at a much lower frequency, indicating that they represent effector cells that are truly terminally differentiated. The combination of KLRG1 and CD57 expression might thus aid in refining functional characterization of CD8(+) T cell subsets.

The increase of CD57+ T cells in the peripheral blood and their impaired immune functions in patients with advanced gastric cancer

In addition to natural killer (NK) cells, T cells expressing natural killer cell markers, CD56 or CD57 (NK type T cells), have been considered to play an important role in antitumor immunity. We examined the proportion of NK cell and NK type T cell subsets in the peripheral blood from patients with gastric cancer. The IFN-gamma production capacity and population of cytoplasmic perforin positive cells in peripheral blood mononuclear cells (PBMC) were evaluated. Peripheral blood samples were obtained from 56 patients with gastric cancer and 21 healthy volunteers. The proportion of CD56- CD57+ T cells (CD57+ T cells) was significantly higher in advanced gastric cancer patients than those in healthy volunteers and patients with early stage gastric cancer, whereas no correlation was observed between the proportion of CD56+ T cells or NK cells and tumor progression. Furthermore, a significant decrease of CD8+ CD57+ T cells was found in patients with advanced gastric cancer. The proportion of CD57+ T cells did not correlate with interferon-gamma (IFN-gamma) production from PBMC in gastric cancer patients, although a significant correlation was found between them in healthy volunteers. The proportion of perforin positive CD57+ T cells, especially CD8+ CD57+ T cells, in patients with gastric cancer was markedly lower than that in healthy volunteers. Collectively, although the proportion of CD57+ T cells in PBMC was found to increase with tumor progression, their function in antitumor immunity is impaired in patients with gastric cancer.

Roles of HNK-1 carbohydrate epitope and its synthetic glucuronyltransferase genes on migration of rat neural crest cells

HNK-1 carbohydrate epitope is localized on the surface of avian neural crest cells (NCCs), and is necessary for their migration. However, it is still disputed whether the epitope works in similar ways in mammalian embryos. In this study, we found that HNK-1 carbohydrate epitope was specifically detected in some of the cranial ganglia, migrating trunk NCCs and some non-NCC derivatives in the rat embryo. Two genes encoding glucuronyltransferases that synthesize the HNK-1 epitope in vitro (GlcAT-P and GlcAT-D) were recently identified in the rat. Interestingly, the NCCs in the cranial ganglia expressed the GlcAT-D gene, whereas the migrating trunk NCCs expressed the GlcAT-P gene. To investigate in vivo functions of the GlcATs in the NCC migration further, we overexpressed GlcAT genes by electroporation in the cranial NCCs in cultured rat embryos. Transfection of both GlcAT genes resulted in efficient synthesis of the HNK-1 epitope in the NCCs. GlcAT-P overexpression increased distance of cranial NCC migration, whereas GlcAT-D overexpression did not show this effect. Our data suggest that the HNK-1 epitope synthesized by different GlcATs is involved in migration in the sublineages of the NCCs in the rat embryo, and that GlcAT-P and GlcAT-D mediate different effects on the NCC migration.

Antibodies to myelin-associated glycoprotein accelerate preferential motor reinnervation

Predegeneration of nerve enhances its ability to support axon regeneration. Trophic factors are upregulated by reactive Schwann cells while potentially inhibitory molecules are removed. These experiments isolate the effects of one such inhibitory molecule, the myelin-associated glycoprotein (MAG), to determine its role in modifying regeneration after nerve repair. Suture of the mouse femoral nerve was followed by daily intraperitoneal injection of antibodies to MAG, antibodies to HNK-1, a specific muscle pathway marker, or no further treatment. Regeneration was assayed by double-labeling the femoral cutaneous and muscle branches with horseradish peroxidase and fluoro-gold after 4 weeks or 6 weeks of regeneration. Four weeks after nerve repair, selective reinnervation of the muscle branch by motoneurons, or preferential motor reinnervation (PMR), was not seen in either controls or L2-antibody-treated animals. In contrast, treatment with MAG antibodies resulted in dramatic PMR. By 6 weeks, the controls had achieved borderline specificity, substantial PMR developed in the L2 antibody group and the MAG group changed little. Blocking access to MAG in the distal nerve stump thus accelerated and enhanced PMR. Sensory regeneration was depressed by both antibody treatments at 4 weeks but recovered by 6 weeks. Antibody administration has a generalized effect on sensory regeneration that is unrelated to the behavior of motoneurons in the same nerve.

Expression of CD57 defines replicative senescence and antigen-induced apoptotic death of CD8+ T cells

Virus-specific CD8(+) T-cell responses play a pivotal role in limiting viral replication. Alterations in these responses, such as decreased cytolytic function, inappropriate maturation, and limited proliferative ability could reduce their ability to control viral replication. Here, we report on the capacity of HIV-specific CD8(+) T cells to secrete cytokines and proliferate in response to HIV antigen stimulation. We find that a large proportion of HIV-specific CD8(+) T cells that produce cytokines in response to cognate antigen are unable to divide and die during a 48-hour in vitro culture. This lack of proliferative ability of HIV-specific CD8(+) T cells is defined by surface expression of CD57 but not by absence of CD28 or CCR7. This inability to proliferate in response to antigen cannot be overcome by exogenous interleukin-2 (IL-2) or IL-15. Furthermore, CD57 expression on CD8(+) T cells, CD4(+) T cells, and NK cells is a general marker of proliferative inability, a history of more cell divisions, and short telomeres. We suggest, therefore, that the increase in CD57(+) HIV-specific CD8(+) T cells results from chronic antigen stimulation that is a hallmark of HIV infection. Thus, our studies define a phenotype associated with replicative senescence in HIV-specific CD8(+) T cells, which may have broad implications to other conditions associated with chronic antigenic stimulation.

Function and molecular modeling of the interaction between human interleukin 6 and its HNK-1 oligosaccharide ligands

Interleukin 6 (IL-6) is endowed with a lectin activity for oligosaccharide ligands possessing the HNK-1 epitope (3-sulfated glucuronic acid) found on some mammalian glycoprotein N-glycans (Cebo, C., Dambrouck, T., Maes, E., Laden, C., Strecker, G., Michalski, J. C., and Zanetta, J. P. (2001) J. Biol. Chem. 276, 5685-5691). Using high affinity oligosaccharide ligands, it is demonstrated that this lectin activity is responsible for the early dephosphorylation of tyrosine residues found on specific proteins induced by interleukin 6 in human resting lymphocytes. The gp130 glycoprotein, the signal-transducing molecule of the IL-6 pathway, is itself a molecule possessing the HNK-1 epitope. This indicates that IL-6 is a bi-functional molecule able to extracellularly associate its alpha-receptor with the gp130 surface complex. Computational modeling indicates that the lower energy conformers of the high affinity ligands of IL-6 have a common structure. Docking experiments of these conformers suggest that the carbohydrate recognition domain of IL-6 is localized in the domain previously identified as site 3 of IL-6 (Somers, W., Stahl, M., and Seehra, J. S. (1997) EMBO J. 16, 989-997), already known to be involved in interactions with gp130.

Antibody to the HNK-1 glycoepitope affects fasciculation and axonal pathfinding in the developing posterior lateral line nerve of embryonic zebrafish

The HNK-1 glycoepitope, carried by many cell recognition molecules, is present in the developing posterior lateral line nerve and on other primary axons of zebrafish. To elucidate the function of HNK-1 in vivo, the antibody 412 to HNK-1 was injected into zebrafish embryos at 16 h post fertilization (hpf). The injected antibody bound specifically to axons carrying HNK-1. This treatment selectively affected the growth of either one or both posterior lateral line nerves in 39% of the experimental cases (13 of 33 animals), which was significantly more (P<0.0002) than in uninjected, vehicle injected, and non-immune IgG injected controls (1.2% of the animals; one of 85 animals), as assessed at 27 or 33 hpf. Other HNK-1 immunoreactive nerves, such as the ventral motor nerves were unaffected, indicating that antibody binding per se did not interfere with axon growth. The primordium of the posterior lateral line was not affected in its caudal migration and in depositing differentiating neuromasts along the trunk, showing that injections did not retard development and that initial formation of lateral line organs is probably independent of contact with nerve fibers. We suggest that the HNK-1 glycoepitope is an important modulator of embryonic nerve growth.

[Roles of the HNK-1 carbohydrate epitope in the nervous system]

The HNK-epitope, 3-sulfo-glucuronyl residue is expressed specifically on a series of cell adhesion molecules and on some glycolipids in the nervous system over a wide range of species, and its expression is spatially and temporally regulated during the development of the nervous system. To study the biological functions of the epitope, we have cloned the enzymes that are involved in the biosynthesis of the epitope, glucuronyltransferase (GlcAT-P and GlcAT-S) and sulfotransferase (Sulf-T), A Northern blot analysis of GlcAT mRNAs in various rat tissues indicated that GlcAT-P and -S are the brain-specific or neural-specific enzymes. Upon transfection of the full length GlcAT-P cDNA into COS-1 cells, which do not express the HNK-lepitope, cells were transformed into HNK-1 positive cells. These cells showed dramatic changes of the cell architecture. They had long and branched processes with irregular shapes and several micro spikes on the soma and processes. Another function of the HNK-1 epitope is the inhibition of cell-cell aggregation. Thus control COS-1 cells formed huge aggregates after incubation at room temperature for 90 min, and most of the HNK-1 positive cells remained as free single cells.

Active roles of caspase-3 in human gastric carcinoma cell death by apoptosis inducing nucleosides from CD57+HLA-DRbright natural suppressor cell line

The six apoptosis inducing nucleosides (AINs), which were isolated by high performance liquid chromatography from CD57+HLA-DRbright natural suppressor (57.DR-NS) cell cultures, induced apoptosis in human gastric carcinoma (GCIY) cells demonstrating the accumulation of sub-G1 DNA content and morphological changes. By means of DNA unwinding assay, it has been revealed that DNA strand breaks were initially involved in the apoptotic cell death of GCIY cells treated with AINs followed by activation of caspase cascades, especially caspase-3. Actually, the cleavage of fluorogenic substrate for caspase-3 was identified in the reaction. Whereas, the addition of caspase-3 inhibitor into the reaction prevented the cleavage of fluorogenic substrate for caspase-3 and resulted in the blockage of the sub-G1 DNA accumulation and DNA fragmentation as apoptotic signals. Thus, it was definitely elucidated that the activation of caspase-3 displayed a key feature during AIN-induced apoptosis in GCIY cells.

The HNK-1 carbohydrate epitope in the eye: basic science and functional implications

The HNK-1 carbohydrate epitope is part of many cell membrane and extracellular matrix molecules. It has been implicated in cell to cell and cell to extracellular matrix adhesion, and antibodies to the HNK-1 epitope are emerging as a versatile tool in eye research. They have been used to identify a novel cell type in the human eye, the subepithelial matrix cells that reside in the inner connective tissue layer (ICTL) of the ciliary body. Although these cells resemble fibroblasts in ultrastructure, they form a distinct cell population that differs in its antigenic profile from fibroblasts of other tissues. These cells are associated with the elastic fiber system of the ICTL. Other structures in the human eye that harbor the HNK-1 epitope in a nonrandom pattern are the ciliary and iris epithelia, the zonular lamella, the lens capsule, the retina, glial cells of the optic and ciliary nerves, and scleral fibroblasts. The HNK-1 epitope in the eye appears early during embryonic development and is phylogenetically conserved, but many interspecies differences exist in its distribution. The role of the HNK-1 epitope may be to structurally stabilize the ciliary body and the retina, and to participate in zonular attachments. The HNK-1 epitope has been linked with many common eye diseases. The subepithelial matrix cells seem to be susceptible to undergo irreversible damage as a result of glaucoma, thermal injury, and tissue compression. This epitope has proved to be useful in identifying intraocular deposits of exfoliation syndrome. It can explain the adhesiveness of exfoliation material. Intraocular exfoliation material differs in HNK-1 immunoreactivity from the extraocular fibrillopathy of exfoliation syndrome and its presence in fellow eyes also argues against the concept of unilateral exfoliation syndrome. The HNK-1 epitope is found in the extracellular matrix of secondary cataract and anterior subcapsular cataract, and it may contribute to their pathogenesis. Finally, the HNK-1 epitope can be used to trace neuroepithelial derivatives of the optic vesicle in developmental anomalies and in tumors of the eye. Eventual identification of molecules that bear the HNK-1 epitope in the eye will likely shed light on many aspects of ocular physiology and pathobiology

Functional analysis of the CD8+CD57+ cell population in normal healthy individuals and matched unrelated T-cell-depleted bone marrow transplant recipients

The biological activities of CD8+ that co-express CD57 remain poorly defined. It is unclear whether all CD8+ cells have the potential to become CD57+ or whether they represent a unique subset with distinct functions. Several studies have reported the association between elevated numbers of CD8+CD57+ and a wide range of clinical disorders such as viral reactivation of human cytomegalovirus (HCMV). In this study, we have investigated the relationship between viral reactivation and the effect of diminished interleukin (IL)-2 production. Using CD8+ cells isolated from patients at various times after allogeneic transplants and in vitro models of HCMV infection, we determined their combined effect on CD8+CD57+. Our results show that high numbers of CD8+CD57+ correlated with diminished killing of HCMV-infected targets. In addition, we showed a synergistic effect between IL-2 and HCMV in the expansion of CD8+CD57+ cells. Furthermore, these cells after anti-CD3 stimulation did not produce tumour necrosis factor (TNF)-alpha or interferon (IFN)-gamma. Interestingly, IL-10 production was elevated in several patients which appeared to be associated with the time from transplant.

Binding of human cytomegalovirus to sulfated glucuronyl glycosphingolipids and their inhibitory effects on the infection

Interactions between human cytomegalovirus (HCMV) and various carbohydrate structures were analysed using sulfated glucuronyl glycosphingolipids (SGGLs) and the structurally related glycosphingolipids (GLs). A thin-layer chromatography-overlay assay and a solid-phase binding assay revealed that HCMV strongly bound to sulfated glucuronyl lactosaminylparagloboside, one of the SGGLs having the repeating lactosamine structure (3Gal beta1-4GlcNAc1-)2 in addition to the 3-O-sulfated glucuronyl moiety. The virus bound less strongly to other 3-O-sulfated GLs, which included sulfated glucuronyl paragloboside and cerebroside sulfate ester, and also to (3Gal beta1-4GlcNAc1-)2-containing GLs that included nLc6Cer. Thus, a (3Gal beta1-4GlcNAc1-)2 and a 3-O-sulfated saccharide seem to be important structures for the binding by HCMV. When virus particles were preincubated with these GLs, inhibitory effects were observed both on expression of the viral immediate-early gene and on plaque formation by HCMV. These effects were very well correlated with the abilities of the GLs to bind to the virus. Pretreatment of host cells with HNK-1 monoclonal antibody, which specifically recognizes SGGLs, resulted in partial inhibition of plaque formation by HCMV. These results clearly show that HCMV recognizes and binds to the sulfated carbohydrate structure in SGGL and also suggest that binding of HCMV to the specific sugar structure may play an important role in HCMV infection.

[Molecular biological approach to functions of telencephalin, a cell adhesion molecule and HNK-1 carbohydrate epitope, which is commonly expressed on cell adhesion molecules in the nervous system]

Cell surface carbohydrates modulate a variety of cellular functions, including recognition and adhesion. The HNK-1 carbohydrate epitope, which is recognized by the monoclonal antibody HNK-1, is specifically expressed on a series of cell adhesion molecules and also on some glycolipids in the nervous system over a wide range of species from insect to mammal. The HNK-1 epitope is spatially and temporally regulated during the development of the nervous system and associated with neural crest cell migration, neuron to glial cell adhesion, outgrowth of astrocytic processes and migration of cell body, as well as the preferential outgrowth of neurites from motor neurons. These observations together with the unusual chemical nature of the HNK-1 epitope, namely a non-reducing terminal 3-sulfoglucuronic acid residue, prompted us to study the biosynthesis of the NHK-1 epitope, in which a unique glucuronyltransferase(s) plays a key role. We found that the respective glucuronyltransferases are involved in the biosynthesis of the HNK-1 epitope on glycoproteins (GlcAT-P) and on glycolipids (GlcAT-L). Then, we isolated a novel glucuronyltransferase (GlcAT-P) specific for glycoprotein substrates and its cDNA from the rat brain. The primary structure deduced from the cDNA sequence predicted a type II transmembrane protein with 347 amino acids. Transfection of the GlcAT-P cDNA into COS-1 cells induced not only expression of the HNK-1 epitope on the cell surface but also marked morphological changes of the cells, suggesting that the HNK-1 epitope was associated with the cell-substratum interaction. The GlcAT-P cDNA obtained in this study will be a useful molecular tool to open the way for further steps in the elucidation of the biological function of the HNK-1 carbohydrate epitope in the development of the nervous system.

HNK-1 antigens on uveal and cutaneous melanoma cell lines

The HNK-1 epitope has been associated with the metastatic behaviour of uveal melanomas. We characterized HNK-1 antigens on four human uveal (primary and metastatic) and two primary cutaneous melanoma cell lines by immunocytochemistry and Western blot analysis. We also determined the involvement of the HNK-1 epitope in cell-cell interactions on a matrigel layer. Three uveal melanoma cell lines (one primary and two metastatic) and one cutaneous melanoma cell line showed HNK-1 expression by immunocytochemistry. On matrigel, only the HNK-1-positive cutaneous melanoma cell line Bowes grew in a honeycomb-like structure which disappeared after adding HNK-1 antibodies to the culture medium. Immunoblot analysis of the primary uveal melanoma cell line EOM-3 revealed five HNK-1-positive protein bands with apparent molecular weights of 200, 160, 115, 95 and 75 kDa. The cutaneous melanoma cell line Bowes showed three HNK-1-positive protein bands with apparent molecular weights of 150, 135 and 90 kDa. This study shows that two uveal (primary and metastatic) and one primary cutaneous melanoma cell lines express HNK-1 antigens on immunoblot. Only in the HNK-1-positive cutaneous melanoma cell line Bowes did the HNK-1 epitope have a function in intercellular adhesion. Although the primary uveal melanoma cell line EOM-3 showed a similar HNK-1 immunoreactivity, we could not demonstrate HNK-1-mediated cell adhesion. On immunoblot, the two cell lines displayed different HNK-1 antigens, which may explain the difference in cell adhesion.

Clonal predominance of cytomegalovirus-specific CD8+ cytotoxic T lymphocytes in bone marrow recipients

After lymphocyte-depleted BMT, CD8+ T cells have been expanded to or above normal levels in 45% of the recipients within 3 months. The mechanisms underlying proliferation of donor-derived CD8+ T cells after BMT are still unclear. We investigated whether these CD8+ T cells proliferate in response to specific antigens by determination of TCR clonality and whether these cells exert specific cytotoxicity. PCR analysis of TCR-gamma gene rearrangements showed a marked clonal predominance in CD8+ T cells of recipients with a high number of these cells. Strong association between expansion of CD8+ T cells and CMV infection suggests involvement of CMV antigens. Therefore, we examined CMV-specific cytotoxicity of freshly isolated CD8+ T cells of two BMT recipients with clonal expansion after the onset of CMV infection. CD8+ T cells exerted HLA-restricted cytotoxicity directed against CMV-infected fibroblasts indicating that CMV stimulates proliferation. The majority of CD8+ T cells in these recipients expressed CD57. We demonstrated that TCR clonality was irrespective of CD57 expression. Both CD8+CD57+ and CD8+CD57- T cells showed significant HLA-restricted CMV-specific cytotoxicity. These studies strongly suggest that CMV antigens can induce expansion of clonal CD8+ T cells after BMT.