A Call for Gene Expression Analysis in Whole Blood of Patients With Rheumatoid Arthritis (RA) as a Biomarker for RA-Associated Interstitial Lung Disease

OBJECTIVE

Rheumatoid arthritis (RA)-associated interstitial lung disease (ILD) is one of the most common and prognostic organ manifestations of RA. Therefore, to allow effective treatment, it is of crucial importance to diagnose RA-ILD at the earliest possible stage. So far, the gold standard of early detection has been high-resolution computed tomography (HRCT) of the lungs. This procedure involves considerable radiation exposure for the patient and is therefore unsuitable as a routine screening measure for ethical reasons. Here, we propose the analysis of characteristic gene expression patterns as a biomarker to aid in the early detection and initiation of appropriate, possibly antifibrotic, therapy.

METHODS

To investigate unique molecular patterns of RA-ILD, whole blood samples were taken from 12 female patients with RA-ILD (n = 7) or RA (n = 5). The RNA was extracted, sequenced by RNA-Seq, and analyzed for characteristic differences in the gene expression patterns between patients with RA-ILD and those with RA without ILD.

RESULTS

The differential gene expression analysis revealed 9 significantly upregulated genes in RA-ILD compared to RA without ILD: arginase 1 (ARG1), thymidylate synthetase (TYMS), sortilin 1 (SORT1), marker of proliferation Ki-67 (MKI67), olfactomedin 4 (OLFM4), baculoviral inhibitor of apoptosis repeat containing 5 (BIRC5), membrane spanning 4-domains A4A (MS4A4A), C-type lectin domain family 12 member A (CLEC12A), and the long intergenic nonprotein coding RNA (LINC02967).

CONCLUSION

All gene products of these genes (except for LINC02967) are known from the literature to be involved in the pathogenesis of fibrosis. Further, for some, a contribution to the development of pulmonary fibrosis has even been demonstrated in experimental studies. Therefore, the results presented here provide an encouraging perspective for using specific gene expression patterns as biomarkers for the early detection and differential diagnosis of RA-ILD as a routine screening test.

Reversible phosphorylation of a lectin-receptor-like kinase controls xylem immunity

Pattern-recognition receptors (PRRs) mediate basal resistance to most phytopathogens. However, plant responses can be cell type specific, and the mechanisms governing xylem immunity remain largely unknown. We show that the lectin-receptor-like kinase LORE contributes to xylem basal resistance in Arabidopsis upon infection with Ralstonia solanacearum, a destructive plant pathogen that colonizes the xylem to cause bacterial wilt. Following R. solanacearum infection, LORE is activated by phosphorylation at residue S761, initiating a phosphorelay that activates reactive oxygen species production and cell wall lignification. To prevent prolonged activation of immune signaling, LORE recruits and phosphorylates type 2C protein phosphatase LOPP, which dephosphorylates LORE and attenuates LORE-mediated xylem immunity to maintain immune homeostasis. A LOPP knockout confers resistance against bacterial wilt disease in Arabidopsis and tomatoes without impacting plant growth. Thus, our study reveals a regulatory mechanism in xylem immunity involving the reversible phosphorylation of receptor-like kinases.

Identification of two early blood biomarkers ACHE and CLEC12A for improved risk stratification of critically ill COVID-19 patients

In order to identify biomarkers for earlier prediction of COVID-19 outcome, we collected blood samples from patients with fatal outcomes (non-survivors) and with positive clinical outcomes (survivors) at ICU admission and after seven days. COVID-19 survivors and non-survivors showed significantly different transcript levels for 93 genes in whole blood already at ICU admission as revealed by RNA-Seq. These differences became even more pronounced at day 7, resulting in 290 differentially expressed genes. Many identified genes play a role in the differentiation of hematopoietic cells. For validation, we designed an RT-qPCR assay for C-type lectin domain family 12 member A (CLEC12A) and acetylcholinesterase (ACHE), two transcripts that showed highest potential to discriminate between survivors and non-survivors at both time points. Using our combined RT-qPCR assay we examined 33 samples to accurately predict patient survival with an AUROC curve of 0.931 (95% CI = 0.814-1.000) already at ICU admission. CLEC12A and ACHE showed improved prediction of patient outcomes compared to standard clinical biomarkers including CRP and PCT in combination (AUROC = 0.403, 95% CI = 0.108-0.697) or SOFA score (AUROC = 0.701 95% CI = 0.451-0.951) at day 0. Therefore, analyzing CLEC12A and ACHE gene expression from blood may provide a promising approach for early risk stratification of severely ill COVID-19 patients.

Potential biomarkers for the prognosis and treatment of HCC immunotherapy

OBJECTIVE

The liver is a unique organ containing large populations of immune cells. Immunotherapy for liver cancer is a promising yet particularly challenging method. Therefore, it harbors great significance for the identification of immune-related subtypes and the potential therapeutic targets for hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Firstly, we classified the HCC samples downloaded from the dataset of Cancer Genome Atlas (TCGA) into two clusters based on the immune cell infiltration. Thereafter, we identified the significant module and regulatory factors using the weighted gene co-expression network analysis (WGCNA). The immune competence of the regulatory factors was delineated through the ESTIMATE algorithm, the analysis of the tumor microenvironment, and pan-cancer analysis. In the single-cell RNA sequencing analysis, we further explored the immune competence of regulatory factors. We also collected the potential drugs targeting the regulatory factors. In addition, we constructed lncRNA-miRNA-mRNA interaction regulatory networks. Finally, western blot and quantitative real-time polymerase chain reaction (qRT-PCR) were conducted to verify the protein expression of regulatory genes in HCC cell lines and tissues.

RESULTS

According to the immune cell infiltration, two immune-related subtypes-cluster 1 and cluster 2-were found. Patients in cluster 2 had a more significant immune infiltration than in cluster 1. Afterward, six significant regulatory genes were identified through WGCNA, and the expression in cluster 2 was high in cluster 1. We performed a comprehensive analysis to clarify the immune signature. The results showed that the six genes had significant immunological competence. Moreover, the expression of the six genes was similar to the subtypes' classification. In the analysis of the prognosis value, patients in cluster 2 had a better prognosis. In addition, the lncRNA in the lncRNA-miRNA-mRNA interaction regulatory networks was located in the nucleus and cytoplasm. In the single-cell RNA sequencing analysis, the six genes were related to the immune cell. We also identified potential drugs for CD6 and CLEC12A, which may provide potential therapeutic drugs. Finally, the regulatory genes were verified in the western blot and quantitative real-time polymerase chain reaction.

CONCLUSIONS

The classification into two clusters based on the immune cell infiltration may provide a promising prospect for HCC through immunotherapy. The six regulatory genes may be potential therapeutic targets in the treatment of HCC.

Antifungal immunity mediated by C-type lectin receptors may be a novel target in immunotherapy for urothelial bladder cancer

Immunotherapies, such as immune-checkpoint blockade and adoptive T-cell therapy, offer novel treatment options with good efficacy for patients with urothelial bladder cancer. However, heterogeneity and therapeutic resistance have limited the use of immunotherapy. Further research into immune-regulatory mechanisms in bladder cancer is urgently required. Emerging evidence demonstrates that the commensal microbiota and its interactions with host immunity play pivotal roles in a variety of physiological and pathological processes, including in cancer. The gut microbiota has been identified as a potentially effective target of treatment that can be synergized with immunotherapy. The urothelial tract is also a key site for multiple microbes, although the immune-regulatory role of the urinary microbiome in the process of carcinogenesis of bladder cancer remains to be elucidated. We performed a comprehensive analysis of the expression and biological functions of C-type lectin receptors (CLRs), which have been recognized as innate pathogen-associated receptors for fungal microbiota, in bladder cancer. In line with previous research on fungal colonization of the urothelial tract, we found that CLRs, including Dectin-1, Dectin-2, Dectin-3, and macrophage-inducible Ca²⁺-dependent lectin receptor (Mincle), had a significant association with immune infiltration in bladder cancer. Multiple innate and adaptive pathways are positively correlated with the upregulation of CLRs. In addition, we found a significant correlation between the expression of CLRs and a range of immune-checkpoint proteins in bladder cancer. Based on previous studies and our findings, we hypothesize that the urinary mycobiome plays a key role in the pathogenesis of bladder cancer and call for more research on CLR-mediated anti-fungal immunity against bladder cancer as a novel target for immunotherapy in urothelial bladder cancer.

Arsenic exposure and human blood DNA methylation and hydroxymethylation profiles in two diverse populations from Bangladesh and Spain

BACKGROUND

Associations of arsenic (As) with the sum of 5-mC and 5-hmC levels have been reported; however, As exposure-related differences of the separated 5-mC and 5-hmC markers have rarely been studied.

METHODS

In this study, we evaluated the association of arsenic exposure biomarkers and 5-mC and 5-hmC in 30 healthy men (43-55 years) from the Aragon Workers Health Study (AWHS) (Spain) and 31 healthy men (31-50 years) from the Folic Acid and Creatinine Trial (FACT) (Bangladesh). We conducted 5-mC and 5-hmC profiling using Infinium MethylationEPIC arrays, on paired standard and modified (ox-BS in AWHS and TAB in FACT) bisulfite converted blood DNA samples.

RESULTS

The median for the sum of urine inorganic and methylated As species (ΣAs) (μg/L) was 12.5 for AWHS and 89.6 for FACT. The median of blood As (μg/L) was 8.8 for AWHS and 10.2 for FACT. At a statistical significance p-value cut-off of 0.01, the differentially methylated (DMP) and hydroxymethylated (DHP) positions were mostly located in different genomic sites. Several DMPs and DHPs were consistently found in AWHS and FACT both for urine ΣAs and blood models, being of special interest those attributed to the DIP2C gene. Three DMPs (annotated to CLEC12A) for AWHS and one DHP (annotated to NPLOC4) for FACT remained statistically significant after false discovery rate (FDR) correction. Pathways related to chronic diseases including cardiovascular, cancer and neurological were enriched.

CONCLUSIONS

While we identified common 5-hmC and 5-mC signatures in two populations exposed to varying levels of inorganic As, differences in As-related epigenetic sites across the study populations may additionally reflect low and high As-specific associations. This work contributes a deeper understanding of potential epigenetic dysregulations of As. However, further research is needed to confirm biological consequences associated with DIP2C epigenetic regulation and to investigate the role of 5-hmC and 5-mC separately in As-induced health disorders at different exposure levels.

A novel IgG-based FLT3xCD3 bispecific antibody for the treatment of AML and B-ALL

BACKGROUND

In lymphoid malignancies, the introduction of chimeric antigen receptor T (CAR-T) cells and bispecific antibodies (bsAbs) has achieved remarkable clinical success. However, such immunotherapeutic strategies are not yet established for acute myeloid leukemia (AML), the most common form of acute leukemia in adults. Common targets in AML such as CD33, CD123, and CLEC12A are highly expressed on both AML blasts and on normal myeloid cells and hematopoietic stem cells (HSCs), thereby raising toxicity concerns. In B-cell acute lymphoblastic leukemia (B-ALL), bsAbs and CAR-T therapy targeting CD19 and CD22 have demonstrated clinical success, but resistance via antigen loss is common, motivating the development of agents focused on alternative targets. An attractive emerging target is FLT3, a proto-oncogene expressed in both AML and B-ALL, with low and limited expression on myeloid dendritic cells and HSCs.

METHODS

We developed and characterized CLN-049, a T cell-activating bsAb targeting CD3 and FLT3, constructed as an IgG heavy chain/scFv fusion. CLN-049 binds the membrane proximal extracellular domain of the FLT3 protein tyrosine kinase, which facilitates the targeting of leukemic blasts regardless of FLT3 mutational status. CLN-049 was evaluated for preclinical safety and efficacy in vitro and in vivo.

RESULTS

CLN-049 induced target-restricted activation of CD4+ and CD8+ T cells. AML cell lines expressing a broad range of surface levels of FLT3 were efficiently lysed on treatment with subnanomolar concentrations of CLN-049, whereas FLT3-expressing hematopoietic progenitor cells and dendritic cells were not sensitive to CLN-049 killing. Treatment with CLN-049 also induced lysis of AML and B-ALL patient blasts by autologous T cells at the low effector-to-target ratios typically observed in patients with overt disease. Lysis of leukemic cells was not affected by supraphysiological levels of soluble FLT3 or FLT3 ligand. In mouse xenograft models, CLN-049 was highly active against human leukemic cell lines and patient-derived AML and B-ALL blasts.

CONCLUSIONS

CLN-049 has a favorable efficacy and safety profile in preclinical models, warranting evaluation of its antileukemic activity in the clinic.

Chikungunya Virus Evades Antiviral CD8+ T Cell Responses To Establish Persistent Infection in Joint-Associated Tissues

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes explosive epidemics of a febrile illness characterized by debilitating arthralgia and arthritis that can endure for months to years following infection. In mouse models, CHIKV persists in joint tissues for weeks to months and is associated with chronic synovitis. Using a recombinant CHIKV strain encoding a CD8+ T cell receptor epitope from ovalbumin, as well as a viral peptide-specific major histocompatibility complex class I tetramer, we interrogated CD8+ T cell responses during CHIKV infection. Epitope-specific CD8+ T cells, which were reduced in Batf3-/- and Wdfy4-/- mice with known defects in antigen cross-presentation, accumulated in joint tissue and the spleen. Antigen-specific ex vivo restimulation assays and in vivo killing assays demonstrated that CD8+ T cells produce cytokine and have cytolytic activity. Despite the induction of a virus-specific CD8+ T cell response, the CHIKV burden in joint-associated tissues and the spleen were equivalent in wild-type (WT) and CD8α-/- mice during both the acute and the chronic phases of infection. In comparison, CD8+ T cells were essential for the control of acute and chronic lymphocytic choriomeningitis virus infection in the joint and spleen. Moreover, adoptive transfer of virus-specific effector CD8+ T cells or immunization with a vaccine that induces virus-specific effector CD8+ T cells prior to infection enhanced the clearance of CHIKV infection in the spleen but had a minimal impact on CHIKV infection in the joint. Collectively, these data suggest that CHIKV establishes and maintains a persistent infection in joint-associated tissue in part by evading CD8+ T cell immunity.IMPORTANCE CHIKV is a reemerging mosquito-transmitted virus that in the last decade has spread into Europe, Asia, the Pacific Region, and the Americas. Joint pain, swelling, and stiffness can endure for months to years after CHIKV infection, and epidemics have a severe economic impact. Elucidating the mechanisms by which CHIKV subverts antiviral immunity to establish and maintain a persistent infection may lead to the development of new therapeutic strategies against chronic CHIKV disease. In this study, we found that CHIKV establishes and maintains a persistent infection in joint-associated tissue in part by evading antiviral CD8+ T cell immunity. Thus, immunomodulatory therapies that improve CD8+ T cell immune surveillance and clearance of CHIKV infection could be a strategy for mitigating chronic CHIKV disease.

[The Immunomodulatory Role of C-type Lectin Receptors in Parasitic Infection]

C-type lectins are a group of Ca(2+)-dependent glycan-binding proteins. The C-type lectin receptors (CLRs) recognize carbohydrate ligands in a Ca(2+)-dependent manner. Recent research has demonstrated that CLRs could recognize glycoproteins and activate downstream immune responses. This review summarizes the roles of several CLRs in parasitic infection.

Whole genome analyses of a well-differentiated liposarcoma reveals novel SYT1 and DDR2 rearrangements

Liposarcoma is the most common soft tissue sarcoma, but little is known about the genomic basis of this disease. Given the low cell content of this tumor type, we utilized flow cytometry to isolate the diploid normal and aneuploid tumor populations from a well-differentiated liposarcoma prior to array comparative genomic hybridization and whole genome sequencing. This work revealed massive highly focal amplifications throughout the aneuploid tumor genome including MDM2, a gene that has previously been found to be amplified in well-differentiated liposarcoma. Structural analysis revealed massive rearrangement of chromosome 12 and 11 gene fusions, some of which may be part of double minute chromosomes commonly present in well-differentiated liposarcoma. We identified a hotspot of genomic instability localized to a region of chromosome 12 that includes a highly conserved, putative L1 retrotransposon element, LOC100507498 which resides within a gene cluster (NAV3, SYT1, PAWR) where 6 of the 11 fusion events occurred. Interestingly, a potential gene fusion was also identified in amplified DDR2, which is a potential therapeutic target of kinase inhibitors such as dastinib, that are not routinely used in the treatment of patients with liposarcoma. Furthermore, 7 somatic, damaging single nucleotide variants have also been identified, including D125N in the PTPRQ protein. In conclusion, this work is the first to report the entire genome of a well-differentiated liposarcoma with novel chromosomal rearrangements associated with amplification of therapeutically targetable genes such as MDM2 and DDR2.

Clinical significance of mitogen-induced responses in lymphocytes from patients with chronic lymphocytic leukemia

The mitogenic response patterns as well as surface membrane receptors of peripheral blood lymphocytes were investigated repeatedly during progression of the disease in 27 patients with chronic lymphocytic leukemia. Each patient was characterized by a reproducible mitogenic response pattern. Eleven patients, who required treatment within 0-24 months after diagnosis, had significantly higher cellular responses to dextran sulphate (DxS) and lipopolysaccharide (LPS) than 10 patients who have not required treatment within an observation time of 10-40 months from diagnosis. The high LPS and DxS responses, which may indicate leukemias composed of more immature cells, appear to predict a poor prognosis.

Septate junctions mediate the barrier to paracellular permeability in sea urchin embryos

In sea urchin embryos, blastula formation occurs between the seventh and tenth cleavage and is associated with changes in the permeability properties of the epithelium although the structures responsible for mediating these changes are not known. Tight junctions regulate the barrier to paracellular permeability in chordate epithelia; however, the sea urchin blastula epithelium lacks tight junctions and instead possesses septate junctions. Septate junctions are unique to non-chordate invertebrate cell layers and have a characteristic ladder-like appearance whereby adjacent cells are connected by septa. To determine the function of septate junctions in sea urchin embryos, the permeability characteristics of the embryonic sea urchin epithelia were assessed. First, the developmental stage at which a barrier to paracellular permeability arises was examined and found to be in place after the eighth cleavage division. The mature blastula epithelium is impermeable to macromolecules; however, brief depletion of divalent cations renders the epithelium permeable. The ability of the blastula epithelium to recover from depletion of divalent cations and re-establish a barrier to paracellular permeability using fluorescently labelled lectins was also examined. Finally, septate junction structure was examined in embryos in which the permeability status of the epithelium was known. The results provide evidence that septate junctions mediate the barrier to paracellular permeability in sea urchin embryos.

KLRL1, a novel killer cell lectinlike receptor, inhibits natural killer cell cytotoxicity

Natural killer (NK) cell inhibitory receptors play important roles in the regulation of target susceptibility to natural killing. Here, we report the molecular cloning and functional characterization of a novel NK cell receptor, KLRL1, from human and mouse dendritic cells. KLRL1 is a type II transmembrane protein with an immunoreceptor tyrosine-based inhibitory motif and a C-type lectinlike domain. The KLRL1 gene is located in the central region of the NK gene complex in both humans and mice, on human chromosome 12p13 and mouse chromosome 6F3, adjacent to the other KLR genes. KLRL1 is preferentially expressed in lymphoid tissues and immune cells, including NK cells, T cells, dendritic cells, and monocytes or macrophages. Western blot and fluorescence confocal microscopy analyses indicated that KLRL1 is a membrane-associated glycoprotein, which forms a heterodimer with an as yet unidentified partner. Human and mouse KLRL1 are both predicted to contain putative immunoreceptor tyrosine-based inhibitory motifs (ITIMs), and immunoprecipitation experiments demonstrated that KLRL1 associates with the tyrosine phosphatases SHP-1 (SH2-domain-containing protein tyrosine phosphatase 1) and SHP-2. Consistent with its potential inhibitory function, pretreatment of target cells with human KLRL1-Fc fusion protein enhances NK-mediated cytotoxicity. Taken together, our results demonstrate that KLRL1 belongs to the KLR family and is a novel inhibitory NK cell receptor.

CEACAM1 expression in cutaneous malignant melanoma predicts the development of metastatic disease

PURPOSE

The cell adhesion molecule CEACAM1 is involved in intercellular adhesion and subsequent signal transduction events in a number of epithelia. CEACAM1 downregulation has been demonstrated in colorectal and prostate carcinomas. This study sought to analyze whether its expression in malignant melanoma is associated with metastasis.

PATIENTS AND METHODS

CEACAM1 expression was immunohistochemically evaluated in 100 primary cutaneous malignant melanomas and correlated with metastasis in a 10-year follow-up. Furthermore, CEACAM1 expression was analyzed in metastatic lesions (11 distant metastases and six sentinel lymph node metastases). Univariate Kaplan-Meier analysis and multivariate Cox proportional hazard regression analysis adjusted for standard prognostic indicators were performed to assess the prognostic relevance of CEACAM1 expression.

RESULTS

A total of 28 of 40 patients with CEACAM1-positive primary melanomas developed metastatic disease, compared with only six of 60 patients with CEACAM1-negative melanomas. Often, the strongest CEACAM1 expression was observed at the invading front. In addition, CEACAM1 expression was preserved in the metastatic lesions. Kaplan-Meier analysis revealed a highly significant association between CEACAM1 expression and metastasis (P <.0001); multivariate Cox regression analysis, including CEACAM1 expression status adjusted for tumor thickness, presence of ulceration, and mitotic rate, confirmed that CEACAM1 is an independent factor for the risk of metastasis and demonstrated that the predictive value of CEACAM1 expression is superior to that of tumor thickness.

CONCLUSION

Expression of the cell adhesion molecule CEACAM1 in the primary tumors in melanoma patients is associated with the subsequent development of metastatic disease. This raises the possibility of a functional role for this cell adhesion molecule in the metastatic spread it indicates.

Upregulation of tyrosine kinase TKT by the Epstein-Barr virus transactivator Zta

The Zta protein is a key transactivator involved in initiating the Epstein-Barr virus (EBV) lytic cascade. In addition to transactivating many viral genes, Zta has the capacity to influence host cellular signals by binding to promoter regions or by interacting with several important cellular factors. Based on the observation that tyrosine kinases play central roles in determining the fate of cells, a kinase display assay was used to investigate whether cells expressing Zta have an altered pattern of kinase expression. The assay revealed that TRK-related tyrosine kinase (TKT) is expressed at significant levels in Zta transfectants but not in control cells. Additional evidence was obtained from Northern and Western blotting. Importantly, the upregulation of phosphorylated TKT and TKT downstream effector matrix metalloproteinase 1 in Zta transfectants hinted that TKT might initiate a signaling cascade in Zta-expressing cells. In addition, deletion analysis of the Zta protein revealed that the transactivation and dimerization domains were both essential for the upregulation of TKT transcription. Moreover, correlation of expression levels of Zta and TKT transcripts in nasopharyngeal carcinoma biopsy specimens was clearly demonstrated by quantitative PCR (Q-PCR), which provides the first evidence for an effect of Zta on cellular gene expression in vivo. These findings offer insight into the virus-cell interactions and may help us elucidate the role of EBV in tumorigenesis.

Heterogeneous vascular endothelial growth factor (VEGF) isoform mRNA and receptor mRNA expression in human glomeruli, and the identification of VEGF148 mRNA, a novel truncated splice variant

Vascular endothelial growth factor (VEGF) mediates increased vascular permeability and endothelial mitogenesis, and may orchestrate normal glomerular permselectivity and proteinuria. Distinct isoforms result from differential gene splicing. VEGF binds to two cell surface tyrosine-kinase receptors, KDR (kinase domain region) and Flt-1 (fms-like tyrosine kinase-1). The latter also exists in a soluble form (sFlt), which is inhibitory. We have studied patterns of VEGF-isoform and VEGF-receptor expression in isolated single normal human glomeruli. mRNA from 190 glomeruli (from 20 individuals) was harvested on to magnetic beads, and nested reverse transcription-PCR was performed using primers for the VEGF isoforms and VEGF receptors. Simultaneous nested reverse transcription-PCR for CD45 was conducted in order to exclude leucocyte contamination. Unexpected products were isolated, cloned and sequenced. Multiple patterns of glomerular VEGF mRNA isoform expression were identified. Most frequently (58%), all three common forms were expressed. VEGF(189) (i.e. 189-amino-acid form of VEGF) was expressed in 63%, VEGF(165) in 85% and VEGF(121) in 84% of glomeruli. Two unexpected PCR products were also identified: 18% of glomeruli expressed VEGF(145), and 27% of glomeruli expressed a new truncated VEGF splice variant, VEGF(148), lacking exon 6, the terminal part of exon 7 and exon 8. Multiple patterns of VEGF-receptor expression were also identified, the most common being expression of all three isoforms (28%). Overall, KDR was seen in 59% of glomeruli, Flt-1 in 45% and sFlt in 57%. Thus the expression of VEGF within normal glomeruli is complex and variable, with inter- and intra-individual variation. Furthermore, sFlt appears to be the co-dominant form of VEGF receptor expressed within glomeruli, suggesting that, in healthy individuals, a degree of VEGF autoregulation is the norm. The physiological importance of VEGF(148) remains to be confirmed.

The CD94/NKG2 C-type lectin receptor complex: involvement in NK cell-mediated recognition of HLA class I molecules

A multigene family to human Ig-SF receptors and members of the murine Ly49 C-type lectin family are involved in natural killer (NK) cell-mediated recognition of MHC class I molecules. The human CD94 glycoprotein covalently assembles with different C-type lectins of the NKG2 family. By functional criteria, the CD94/NKG2-A (kp43) receptor complex appears also involved in NK cell-mediated recognition of different HLA class I allotypes. Similarly to the other NK inhibitory receptors, NKG2-A contains cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMS). By contrast, NK clones bearing different receptor complex (CD94/p39) are triggered upon ligation by CD94-specific monoclonal antibodies (MAbs); the p39 subunit is likely encoded by other member(s) of the NKG2 family. Expression of different CD94/NKG2 complexes is warranted to precisely assess their specific interaction with HLA class I molecules, and the molecular basis for their divergent functional properties.

Natural killer cell receptors

In the past year, significant strides have been made in understanding natural killing, the process whereby natural killer cells lyse target cells. Recognition of susceptible targets and activation now appear to be mediated by a natural killer cell receptor that binds carbohydrate determinants on target cells and initiates target lysis. Conversely, receptors have been identified that bind MHC class I molecules on targets that inhibit natural killer cell activation. These findings provide the basis for understanding the molecular processes in the initial steps of natural killing.

Cure of murine candidiasis by recombinant soluble interleukin-4 receptor

Neutralization of interleukin (IL)-4 by specific antibody exerts therapeutic activity in a murine model of systemic candidiasis characterized by strong T helper type 2 (Th2) responses. To investigate whether recombinant soluble IL-4 receptor (sIL-4R) could be used to block IL-4 action in vivo, mice treated with pharmacologic doses of sIL-4R at the time of infection were examined for progression of disease, development of footpad responses, serum IgE levels, and cytokine production in vitro by CD4+ lymphocytes. Following sIL-4R treatment, persistent ablation of circulating IL-4 detected by ELISA was associated with a cure rate of > 90% in otherwise lethally infected mice, onset of durable protection, and a shift from a predominant Th2 to a Th1 pattern of reactivity. In addition, when administered to genetically susceptible adult mice with gastrointestinal yeast colonization, the sIL-4R stimulated Th1-associated anticandidal resistance.

Structure and expression of the Tyro 10 receptor tyrosine kinase

We have isolated cDNA clones encoding Tyro 10, a novel receptor protein-tyrosine kinase (PTK) whose catalytic domain exhibits significant similarity to the Trk family of neurotrophin receptors (Lai & Lemke, 1991). We find that the Tyro 10 gene is widely expressed, both within and outside the nervous system, and in both developing and mature neural tissue. The primary structure of Tyro 10, deduced from cDNA sequence, defines a new sub-family of receptor PTKs. Although the Tyro 10 kinase domain is more closely related to the equivalent domains of Trk, TrkB and TrkC than to the catalytic domains of other receptor PTKs, it is less closely related to these Trk domains than they are to each other. More significantly, the Tyro 10 extracellular (ligand binding) domain is not structurally related to the extracellular domains of the Trk receptors, but instead bears homology to cell surface mediators of protein-protein interactions, including blood coagulation Factors V and VIII, and the neuronal recognition protein A5. These appear to be structural features of a distinct receptor PTK sub-family, in that they are also found in the recently-described discoidin domain receptor (DDR).

Expression of vascular permeability factor (vascular endothelial growth factor) and its receptors in adenocarcinomas of the gastrointestinal tract

Vascular permeability factor (VPF) is one of the most potent known inducers of microvascular hyperpermeability; in addition, it is a selective endothelial cell growth factor, hence its alternate name, vascular endothelial growth factor. VPF exerts its actions on the microvasculature by interacting with specific endothelial cell receptors. VPF is expressed by many transplantable animal tumors, by tumor cell lines in culture, and by certain normal cells in situ. The purpose of the present investigation was to determine whether and with what consistency VPF and its endothelial cell receptors are expressed in primary autochthonous human tumor of gastrointestinal tract origin, as determined by in situ hybridization and immunohistochemistry. Twenty-one primary adenocarcinomas (17 colon, 2 stomach, 1 small bowel, and 1 pancreas) were studied. The malignant epithelial cells expressed VPF mRNA strongly, in contrast to normal epithelium, hyperplastic polyps, and adenomas, which expressed little or no VPF mRNA. VPF expression was further increased in tumor cells immediately adjacent to zones of tumor necrosis; in such areas, occasional stromal cells also expressed VPF mRNA. In the ten colon carcinomas studied, tumor cells stained for VPF protein by immunohistochemistry. The endothelial cells of nearby stromal blood vessels also stained for VPF by immunohistochemistry and in addition expressed mRNAs encoding the VPF receptors flt-1 and kdr as determined by in situ hybridization. Endothelial cells away from the tumor did not stain for VPF and no definite mRNA expression for flt-1 or kdr was detected by in situ hybridization. The ganglion cells of the myenteric plexus of normal bowel expressed VPF mRNA and protein. These data indicate that primary autochthonous human tumors of gastrointestinal origin regularly express both VPF mRNA and VPF protein and that adjacent stromal vessels express mRNAs for both known VPF receptors. VPF is likely to contribute to tumor growth by promoting angiogenesis and stroma formation, both directly, through its action as an endothelial cell growth factor, and indirectly, by increasing vascular permeability, thereby leading to plasma protein extravasation, fibrin deposition, and the eventual replacement of the resulting matrix with vascularized stroma.

Pharmacokinetic parameters and biodistribution of soluble cytokine receptors

The potential use of soluble cytokine receptors as therapeutics in disease states when excessive or prolonged cytokine expression leads to pathogenesis is just beginning (Van Brunt, 1989). The inhibitory effects of soluble receptors have been found to be highly potent and specific for their respective cytokines (Maliszewski and Fanslow, 1990; Maliszewski et al., 1990). Recent in vivo data have shown that exogenously administered soluble receptors can function as cytokine antagonists and suppress autoimmune inflammatory responses (Jacobs et al., 1991a), allograft rejection, and alloreactivity (Fanslow et al., 1990b). The proposed frequency of administration and dosage of a therapeutic agent is dependent on the half-life of the agent and the route of administration. The elimination or half-life of a drug usually depends on its physiochemical properties (molecular size, glycosylation, isoelectric point, and hydrophobic/hydrophilic properties) (DiPalma and DiGregorio, 1990; Katzung, 1984). The half-life will also depend on the mechanism of clearance for that specific receptor. Once pharmacokinetic data are available for soluble receptors, the therapeutic potential of these molecules can be better evaluated. Only limited pharmacokinetic data are currently available for soluble cytokine receptors (Jacobs et al., 1991b). For sIL-1R, the majority of an intravenously administered dose was cleared in the second elimination phase, with a reasonably long half-life (6.3 hr), such that the entire dose was not eliminated until 35 hr. If administration is by subcutaneous injection, the half-life was even more prolonged. One explanation for the prolonged half-life is the minimal distribution to liver and kidneys and thus low levels of clearance by these organs. In contrast, elimination of intravenously administered sIL-4R was relatively rapid, with a short half-life (2.3 hr). This appeared mainly due to liver distribution and clearance, which has been the highest observed for any soluble cytokine receptor. Administering sIL-4R by subcutaneous injection significantly prolonged the half-life. This was most likely due to delaying the rate of liver distribution by slowing the rate of sIL-4R absorption into the circulation. Thus, subcutaneous injection would be the recommended route of administration for this receptor. Construction of a larger dimeric sIL-4R fusion protein did not prolong the i.v. half-life compared to that of the monomer, as the sIL-4R fusion protein was distributed to, and was cleared by, the liver to a greater degree.(ABSTRACT TRUNCATED AT 400 WORDS)

The vascular endothelial growth factor family of polypeptides

Vascular endothelial growth factor (VEGF) was identified as a heparin-binding polypeptide mitogen with a target cell specificity restricted to vascular endothelial cells. Molecular cloning reveals the existence of four species of VEGF having 121, 165, 189, and 206 amino acids. These have strikingly different secretion patterns, which suggests multiple physiological roles for this family of polypeptides. The two shorter forms are efficiently secreted, while the longer ones are mostly cell-associated. Alternative splicing of mRNA, rather that transcription from different genes, is the mechanism for their generation. In situ hybridization reveals that the VEGF mRNA is widely distributed in most tissues and organs and expressed at particularly high levels in areas of active vascular proliferation, like the ovarian corpus luteum. Ligand autoradiography on rat tissue sections demonstrates that VEGF binding sites are associated with vascular endothelial cells of both fenestrated and non-fenestrated capillaries and with the endothelium of large vessels, while no displaceable binding is evident on non-endothelial cell types. These findings support the hypothesis that VEGF plays a highly specific role in the maintenance and in the induction of growth of vascular endothelial cells.

Interleukin 4 receptor targeted cytotoxicity: genetic construction and in vivo immunosuppressive activity of a diphtheria toxin-related murine interleukin 4 fusion protein

The interleukin 4 (IL 4) receptor is expressed on various cells of the immune system, including T and B lymphocytes, macrophages and mast cells. We have constructed a recombinant protein, DAB389-mIL 4, that is composed of the enzymatically active and membrane translocation domains of diphtheria toxin fused to murine IL 4. We demonstrate that this fusion toxin selectively inhibits protein synsthesis in eukaryotic cells which express the murine IL 4 receptor. The cytotoxic potency of this fusion toxin is shown to be directly proportional to the reported number of IL 4 receptors on the surface of target cells. Since the action of DAB389-mIL 4 can be blocked with either excess mIL 4 or antibody to mIL 4, we conclude that its entry into target cells is mediated through the mIL 4 receptor. A mutant form of DAB389-mIL 4, DA(197)B389-mIL 4, in which the fragment A-associated ADP-ribosyltransferase is inactive, is not cytotoxic to murine IL 4 receptor-bearing cells. Finally, we demonstrate that DAB389-mIL 4 administered subcutaneously to DBA/2 mice results in suppression of delayed-type hypersensitivity (DTH); whereas, the non-toxic DA(197)B389-mIL 4 fails to dampen the DTH response.

Plant lectins--histochemical and cytochemical applications in oncology

Lectins are sugar binding proteins or glycoproteins of non-immune origin derived from various plants or animals with specific sugar binding capacity. This property of lectins can be used to identify structural differences between normal and malignant cells. Malignant transformation is accompanied by several changes in cell membrane. Studies have shown that the lectin binding pattern of these cells may indicate the invasive potential of tumours. Lectins can also be used as carriers. Lectins conjugated to chemotherapeutic agents has been found to be more useful in the treatment of tumours induced in animals.

The behavior of human ameloblastoma tissue in collagen matrix in vitro: an immunohistochemical study

We investigated the three-dimensional outgrowth of human ameloblastoma cells cultured in collagen matrix. Growth patterns of four cases of ameloblastoma resembled each other and was characterized by appeared duct-like structures. Case 1 ameloblastoma was subcultured 3 times. Ameloblastoma tissues and cultured cells were stained with various lectins by avidin-biotin peroxidase complex (ABC) staining methods. Both the tissues and cultured cells had the same receptors to Concanavalin ensiforme (Con A), Ricinus communis Agglutinin (RCA-I) and Triticum vulgaris (WGA) but not to Dolichos biflorus (DBA), Ulex europaeus (UEA-1), Soybean (SBA) and Arachis hypogea (PNA). These findings indicated that the cultured cells examined in this study were ameloblastoma cells in origin.

Monocyte activation in rheumatoid arthritis: evidence for in situ activation and differentiation in joints

Monocytes, defined by staining with the Mo-2 and Leu-M3 monoclonal antibodies which both detect the CD14 antigen, were studied in peripheral blood of control subjects and patients with rheumatoid arthritis as well as in rheumatoid synovial fluid of the latter for expression of activation/differentiation markers. The monocytes in the rheumatoid synovial fluids showed increased expression of class II major histocompatibility antigens (HLA-DR and -DQ) and decreased positivity for the peanut agglutinin receptor as compared with those from patient and control peripheral blood. There were no differences in phenotype between the control and patient peripheral blood monocytes. These findings are consistent with the hypothesis that monocytes are activated and differentiate into more mature macrophage-like cells after entry into the rheumatoid joint.

[The relation of changes in the surface markers and the induction of thymocyte functional activity under the action of humoral thymic factors]

Mouse thymocytes were fractionated on PNA+- and PNA-cells. The PNA+-fraction was treated by tactivin--a preparation of thymic hormones. The treatment resulted in the loss of PNA-receptors from the surface of 10-12% of PNA+-cells. The treated suspension was again fractionated by the same method. PNA-thymocytes derived from both the first and the second procedure of fractionation expressed less Thy-1.2 antigen and SBA-receptors than PNA+-cells. Primary and induced PNA-thymocytes were able to produce IL-2 after mitogen stimulation. The data can be interpreted as an evidence of the ability of thymic hormones to induce not only a phenotypical but also a functional maturation of PNA+-thymocytes and of linkage of all the observed signs of maturation.

[Lectin-binding sites in the growing end of rat incisors]

Tooth germs of rat incisors were examined by lectin-histochemistry in the portion from the apical end to enamel forming stage. Tissue sections were prepared from paraformaldehyde-fixed and paraffin-embedded tissues with or without EDTA-decalcification. They were stained with fluorescein-isothiocyanate-labeled (F- for short) lectins and observed by a fluorescent microscope. The boundary between inner enamel epithelia and dental papilla cells was stained with F-Con A, F-MPA and F-PNA. The boundary between the epithelia and dentin was stained with F-Con A and F-MPA. Stratum intermedium cells were stained with F-Con A, F-MPA and F-PNA, and were different in the time when they began to be stained with each lectin during their development. Distal cytoplasm of secretory ameloblasts and odontoblasts were stained with F-MPA and F-Con A, respectively. The staining with these lecting became stronger gradually from the apical to the incisal side. These results suggest that F-MPA and F-Con A are useful as a marker indicating the time when enamel and dentin begins to form, respectively. Distal cytoplasm of secretory ameloblasts was also stained with F-Con A and F-PNA. The odontoblastic layer was stained only with F-Con A, but the dental papilla was stained with F-Con A, F-MPA, and F-PNA. Stellate reticulum and outer enamel epithelia were stained with F-Con A and F-MPA. The comparison of the results from decalcified and non-decalcified tissues showed that the EDTA-decalcification scarcely affected these lectin bindings.

Lectin-carbohydrate interactions. Studies of the nature of hydrogen bonding between D-galactose and certain D-galactose-specific lectins, and between D-mannose and concanavalin A

The binding of galactose-specific lectins from Erythrina indica (EIL), Erythrina arborescens (EAL), Ricinus communis (agglutinin; RCA-I), Abrus precatorius (agglutinin; APA), and Bandeiraea simplicifolia (lectin I; BSL-I) to fluoro-, deoxy-, and thiogalactoses were studied in order to determine the strength of hydrogen bonds between the hydroxyl groups of galactose and the binding sites of the proteins. The results have allowed insight into the nature of the donor/acceptor groups in the lectins that are involved in hydrogen bonding with the sugar. The data indicate that the C-2 hydroxyl group of galactose is involved in weak interactions as a hydrogen-bond acceptor with uncharged groups of EIL and EAL. With RCA-I, the C-2 hydroxyl group forms two weak hydrogen bonds in the capacity of a hydrogen-bond acceptor and a donor. On the other hand, there is a strong hydrogen bond between the C-2 hydroxyl group of galactose, which acts as a donor, and a charged group on BSL-I. The C-2 hydroxyl group of the sugar is also a hydrogen-bond donor to APA. The lectins are involved in strong hydrogen bonds through charged groups with the C-3 and C-4 hydroxyl groups of galactose, with the latter serving as hydrogen-bond donors. The C-6 hydroxyl group of the sugar is weakly hydrogen bonded with neutral groups of EIL, EAL, and APA. With BSL-I, however, a strong hydrogen bond is formed at this position with a charged group of the lectin. The C-6 hydroxyl groups is a hydrogen-bond acceptor for EIL and EAL, a hydrogen-bond donor for APA and BSL-I, and appears not to be involved in binding to RCA-I. The data with the thiosugars indicate the involvement of the C-1 hydroxyl group of galactose in binding to EIL, EAL, and BSL-I, but not to RCA-I and APA. We have also performed a similar analysis of the binding data of fluoro- and deoxysugars to concanavalin A [Poretz, R. D. and Goldstein, I. J. (1970) Biochemistry 9, 2890-2896]. This has allowed comparison of the donor/acceptor properties and free energies of hydrogen bonding of the hydroxyl groups of methyl alpha-D-mannopyranoside to concanavalin A with the results in the present study. On the basis of this analysis, new assignments are suggested for amino acid residues of concanavalin A [corrected] that may be involved in hydrogen bonding to the sugar.

Detecting distant homologies of mosaic proteins. Analysis of the sequences of thrombomodulin, thrombospondin complement components C9, C8 alpha and C8 beta, vitronectin and plasma cell membrane glycoprotein PC-1

Recognition of homologies may give hints about the structure and function of proteins; therefore, we are developing strategies to aid sequence comparisons. Detecting homology of mosaic proteins is especially difficult since the modules constituting these proteins are usually distantly related and their homology is not readily recognized by conventional computer programs. In the present work we show that the rules of the evolution of mosaic proteins can guide the identification of modules of mosaic proteins and can delineate the group of sequences in which the presence of homologous sequences may be expected. By this approach we can concentrate the search for homology to a limited group of sequences; thus ensuring a more intense and more fruitful search. The power of this approach is illustrated by the fact that it could detect homologies not identified by earlier methods of sequence comparison. In this paper we show that thrombomodulin contains a domain homologous with animal lectins, that complement components C9, C8 alpha and C8 beta have modules homologous with one of the repeat units of thrombospondin and that the somatomedin B module of vitronectin is homologous with the internal repeats of plasma cell membrane glycoprotein PC-1.

Identification of glycoproteins expressing tumour-associated PNA-binding sites in colorectal carcinomas by SDS-GEL electrophoresis and PNA-labelling

Many tumour-specific antigens in gastrointestinal cancers have carbohydrate immuno-determinants. These epitopes can be identified by lectins and monoclonal antibodies. By using fluorescein-isothiocyanate (FITC)-conjugated peanut agglutinin (PNA) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) we have investigated glycoproteins carrying altered carbohydrate epitopes in normal and carcinomatous human colorectal mucosa. In normal mucosa PNA stained goblet cell glycoconjugates in the supranuclear (Golgi) distribution. After neuraminidase pretreatment PNA stained actual mucin goblet itself at all levels of the crypts. Colorectal carcinomas displayed a strong and direct binding of PNA to apical cell membranes of carcinomatous cells and intraluminal secretions. Analysis of the glycoproteins by SDS-PAGE and PNA-labelling revealed four carcinoma-associated glycoproteins (26kD, 32kD, 35kD and 50kD). In addition, four glycoproteins (29kD, 30kD, 33kD and 36kD) common to normal and carcinomatous colorectal mucosa could be identified. All of these glycoproteins differed in their molecular weight from those in red cell controls which bind PNA only after desialylation. The study shows that the expression of PNA-binding sites in colorectal carcinomas signifies a cancer-associated carbohydrate alteration. Four carcinoma-associated glycoprotein antigens could be detected by this lectin. The antigens we have identified might be useful in the isolation and purification of more selective reagents for the serologic detection of colorectal cancer.

Studies on glycoproteins in the human malaria parasite Plasmodium falciparum--lectin binding properties and the possible carbohydrate-protein linkage

Several glycoproteins of the human malarial parasite Plasmodium falciparum are shown to bind to the lectins concanavalin A, wheat germ agglutinin, Ricinus communis 120 lectin and Bandeirea simplicifolia lectin. There was reduced binding of [125I]-concanavalin A to several red blood cell glycoproteins, including the anion transport protein, in parasitised cells. The carbohydrates of parasite glycoproteins are not typical N-linked oligosaccharides since the enzyme peptide: N-glyconase F fails to cleave them. In contrast, many of the parasite glycoproteins are labelled with [3H]-myristic acid consistent with a possible linkage of carbohydrate to a membrane anchoring phospholipid.

Glycoconjugates of the human sperm surface: distribution and alterations that accompany capacitation in vitro

We have studied changes in the binding of fluoresceinated lectins to human sperm during in vitro capacitation. We first determined the surface labeling pattern of viable sperm obtained by the swim-up procedure. Sperm were labeled with 100 micrograms/ml FITC-conjugated lectin at 4 degrees C for 30 min. We simultaneously used Hoechst stain 33258 as a supravital stain to help differentiate surface from intracellular lectin labeling. Of 14 lectins studied, six (phytohemagglutinin-E, concanavalin A, Ricinus communis agglutinin-I, and the lectins of wheat germ, Lens culinaris, and Pisum sativum) bound to the entire surface of sperm, sometimes with minor local heterogeneity. Three lectins (from peanut, Maclura pomifera, and soybean) usually bound in a punctate manner, with more label on the tail than on the head. Five lectins (Ulex europaeus, Dolichos biflorus, Helix pomatia, and Vicia villosa lectins, and lectin II of Griffonia simplicifolia) bound very poorly or not at all to the sperm surface. Sperm were also inspected for changes in surface lectin binding patterns after 0, 5, and 23 hr of incubation in a capacitating medium. Two lectins showed reproducible changes. The labeling by Maclura pomifera agglutinin decreased by 5 hr in eight of ten experiments, and among sperm labeled with concanavalin A, the incidence of sperm with a highly fluorescent anterior margin of the sperm head increased by about 3.5-fold between 0 and 5 hr. The labeling pattern of the other lectins did not change.

Detection and characterization of spatial pattern in chimaeric tissue

The mosaic pattern of patches of crypts of Lieberkühn in chimaeric C57BL/6JLac (B6)----DDK mouse small intestine, demonstrated using Dolichos biflorus agglutinin as strain-specific marker, is quantitatively examined using the Greig-Smith analysis of variance. This analysis, widely used in ecological research, provides a method to detect and characterize pattern at various scales. The analysis demonstrates that B6 patches are non-randomly distributed at all scales examined. A consistent increase in the intensity of pattern at one particular scale over all replicate samples identifies 'clusters of clusters' which probably are territories of 'descendent' clones. The sizes of descendent clones, either in terms of numbers of patches or total numbers of crypts, are highly variable. A steady reduction in the strength of pattern from proximal to distal is found. The Greig-Smith analysis of variance provides a valuable method for the analysis of pattern in chimaeric tissue.

A new surface marker on equine peripheral blood lymphocytes. II. Characterization and separation of purified blood lymphocytes with receptors for Helix pomatia A hemagglutinin (HP)

In a preceding report we have shown that the lectin Helix pomatia A hemagglutinin (HP) binds to two subpopulations of neuraminidase-treated equine peripheral blood lymphocytes (PBL), constituting about 20% and 75% of PBL, respectively. The aim of the present study was to further characterize these HP+ cells in regard to other surface markers such as receptors for guinea pig erythrocytes (GPR+ cells), membrane-bound immunoglobulins (sIg+ cells), receptors for activated complement (C3R+ cells) and receptors for IgG (Fc alpha R+ cells). This was done by double marker analysis and by lymphocyte fractionation either on columns charged with HP coupled to Sepharose beads or by rosetting with guinea pig erythrocytes. The fractions were also analysed for their proliferative response in the mixed lymphocyte tumor cell interaction (MLTC) assay and to the mitogens leucoagglutinin (La) and concanavalin A (Con A). The results revealed that the majority of GPR+ cells also expressed high avidity receptors for HP, as defined by means of direct immunofluorescence. These cells constituted a subpopulation of GPR+/HP+ cells T cells comprising approximately 20% of PBL. In contrast, about 75% of the HP+ cells in indirect immunofluorescence were GPR-. The fractionation experiments showed that HP+ and GPR+ cells were probably not B cells since they were sIg-. The C3R+ and Fc alpha R+ lymphocytes were heterogeneous in regard to HP receptors but the majority of these cells was also found in the fractions depleted of HP+ and GPR+ lymphocytes. The fractions eluted from HP columns gave a strong proliferative response in MLTC, whereas fractions depleted of HP+ cells responded poorly. However, in contrast to the GPR+-depleted fractions, those enriched in GPR+ lymphocytes responded poorly to the T cell mitogens La and Con A. The mitogenic response of the HP-column fractions to La and to Con A was variable. The results are discussed in relation to HP being a surface marker for a heterogeneous population of equine T cells.

A new surface marker on equine peripheral blood lymphocytes. I. Subpopulations of lymphocytes with receptors for Helix pomatia A hemagglutinin (HP)

Untreated and neuraminidase-treated equine peripheral blood lymphocytes were analysed for binding of the A hemagglutinin of the snail Helix pomatia (HP). For optimal staining by direct immunofluorescence, the concentration of neuraminidase had to be increased as compared to that needed for other species. Moreover, higher concentrations of HP were required for optimal staining of equine lymphocytes as compared to lymphocytes from other species. Even so, the maximal number of equine lymphocytes exhibiting positive staining was only about 20%. No, or very few, HP-positive lymphocytes were seen when neuraminidase treatment was omitted. However, when the more sensitive method of indirect immunofluorescence was used, approximately 60% of the lymphocytes were HP positive without prior treatment with this enzyme. Neuraminidase treatment significantly increased this figure to about 75%. In all instances, HP binding was specific since it was inhibited by the competitive sugar hapten N-acetyl-D-galactosamine (D-GalNAc) while addition of D-glucose (D-Glc) gave no inhibition. HP binding to neuraminidase-treated lymphocytes was also investigated quantitatively by means of 125I-labeled HP. The number of HP molecules bound per HP-positive cell was approximately 3 X 10(5) and the apparent association constant for the binding of HP to its cellular receptors was approximately 8 X 10(7) 1/mol. No binding of HP to untreated lymphocytes could be recorded in these experiments.

Freeze-etch study of an unmodified lectin interacting with its receptors in model membranes

Experiments are described in which liposomes bearing ganglioside or glycophorin as receptor were exposed to the native (unmodified) lectin, wheat germ agglutinin, and subsequently examined by freeze-etch electron microscopy. Visualized in this way in the absence of lectin, phosphatidylcholine bilayer membranes show no features attributable to the presence of small amounts of glycolipid. Similarly bilayers bearing glycophorin show no obvious etch face (outer surface) features attributable to that species, although they do have intramembranous particles associated with the hydrophobic interior. However, the otherwise smooth and featureless model membrane outer surface permitted ready visualization of bound lectin molecules, and thus the indirect localization of receptors. The lipid membrane itself in the vicinity of receptors was not visibly affected by lectin binding to glycolipid or glycoprotein. The only identifiable lectin-induced change was lateral redistribution of receptor glycoproteins. Ganglioside molecules showed some evidence of existing in small clusters; but their distribution was apparently unaffected by lectin binding. Clumps of lectin bound to glycophorin were found associated predominantly with fluid bilayer regions of phase separated membranes; and lectin distribution on the etch face correlated with intramembranous particle distribution in the fracture face. In contrast, ganglioside lateral distribution was not appreciably influenced by the host lipid matrix phase separation.

[Glycoconjugate cell surfaces as markers of differentiation and malignancy]

The composition of cell membrane-associated glycoproteins and glycolipids is changed during differentiation. Moreover, normal mature cells differ from transformed ones in regard to their glycoconjugate profile. These differences have been analyzed, by means of lectins, concerning intrathymic lymphocytes, T-lymphoma cell lines as well as epithelial carcinomas and tumor cell lines. It was found that lectins recognize molecular structures of the cell membrane which are characteristic of certain developmental stages of intrathymic T-lymphocyte differentiation and, moreover, "tumor"-associated determinants on T-lymphomas as well as on epithelial carcinoma cells.

Interaction between electromagnetic fields and cells: microelectrophoretic effect on ligands and surface receptors

The aggregation between lectins and lymphocyte surface receptors can be affected strongly by a low-level electric field induced in the cell suspension by a time-varying magnetic field. One of the possible mechanisms is the microelectrophoretic effect due to the electric field, which influences the distance (in the mean square sense) between charged ligands and receptors when they are about to separate. On a purely theoretical basis, it is shown that, at low frequencies, an externally induced periodic electric field always decreases the mean lifetime of ligand-receptor complexes. As a consequence, the mitogenic gain obtained by lectin addition to cell suspension is decreased. These results suggest that such a mechanism, if effective, reduces the lectin mitogenic capability and offers a way of handling similar phenomena which have been described for other biological systems.

Molecular analysis of the lymphocyte membrane

Methods for the molecular analysis of lymphocyte membranes are reviewed briefly, and wherever possible presented in a manner relevant to comparative studies. The specific areas reviewed include the bulk isolation of lymphocyte membranes, the use of radioisotopes to covalently label lymphocyte membrane molecules, the use of lectins to characterize membrane glycoconjugates, and our current understanding of lymphocyte membrane immunoglobulins.