CD3-induced T-cell proliferation and interleukin-2 secretion is modulated by the CD45 antigen

α/β-Peptides as Nanomolar Triggers of Lipid Raft-Mediated Endocytosis through GM1 Ganglioside Recognition

Cell delivery of therapeutic macromolecules and nanoparticles is a critical drug development challenge. Translocation through lipid raft-mediated endocytic mechanisms is being sought, as it can avoid rapid lysosomal degradation. Here, we present a set of short α/β-peptide tags with high affinity to the lipid raft-associated ganglioside GM1. These sequences induce effective internalization of the attached immunoglobulin cargo. The structural requirements of the GM1-peptide interaction are presented, and the importance of the membrane components are shown. The results contribute to the development of a receptor-based cell delivery platform.

Immunoprofiling of Drosophila Hemocytes by Single-cell Mass Cytometry

Single-cell mass cytometry (SCMC) combines features of traditional flow cytometry (i.e., fluorescence-activated cell sorting) with mass spectrometry, making it possible to measure several parameters at the single-cell level for a complex analysis of biological regulatory mechanisms. In this study, weoptimizedSCMC to analyze hemocytes of the Drosophila innate immune system. We used metal-conjugated antibodies (against cell surface antigens H2, H3, H18, L1, L4, and P1, and intracellular antigens 3A5 and L2) and anti-IgM (against cell surface antigen L6) to detect the levels of antigens, while anti-GFP was used to detect crystal cells in the immune-induced samples. We investigated the antigen expression profile of single cells and hemocyte populations in naive states, in immune-induced states, in tumorous mutants bearing a driver mutation in the Drosophila homologue of Janus kinase (hop^Tum) and carrying a deficiency of the tumor suppressor gene lethal(3)malignant blood neoplasm-1  [l(3)mbn¹], as well as in stem cell maintenance-defective hdc^Δ84 mutant larvae. Multidimensional analysis enabled the discrimination of the functionally different major hemocyte subsets for lamellocytes, plasmatocytes, and crystal cells, anddelineated the unique immunophenotype of Drosophila mutants. We have identified subpopulations of L2⁺/P1⁺ and L2⁺/L4⁺/P1⁺ transitional phenotype cells in the tumorous strains l(3)mbn¹ and hop^Tum, respectively, and a subpopulation of L4⁺/P1⁺ cells upon immune induction. Our results demonstrated for the first time that SCMC, combined with multidimensional bioinformatic analysis, represents a versatile and powerful tool to deeply analyze the regulation of cell-mediated immunity of Drosophila.

Anti-allergic function and regulatory mechanisms of KR62980 in allergen-induced airway inflammation

The ligand-activated transcription factor, peroxisome proliferator-activated receptor (PPAR)gamma, and its ligands inhibit pro-inflammatory cytokine production by immune cells, thus exerting anti-inflammatory activity. As a non-thiazolidinedione PPARgamma ligand, KR62980 has anti-diabetic and anti-adipogenic activities, but its anti-inflammatory function has yet to be characterized. In this study, we investigated the functions and mechanisms of KR62980 in the activation and differentiation of CD4+ T helper (Th) cells by comparing its effects with those of a thiazolidinedione PPARgamma ligand, rosiglitazone. KR62980 dose-dependently and significantly suppressed TCR-triggered Th cell proliferation by suppressing IL-2/IL-2Ralpha-mediated signaling. Both KR62980 and rosiglitazone suppressed IFNgamma production in a dose-dependent manner, whereas IL-4 gene expression was specifically suppressed by only KR62980. In addition, sustained KR62980 treatment diminished Th2 cytokine production by inhibiting c-Maf expression. In vivo administration of KR62980 in a model of allergic asthma significantly attenuated eotaxin-induced eosinophil infiltration, allergic cytokine production and collagen deposition in the lung. KR62980 also decreased goblet cell hyperplasia in the airway and mucous cell metaplasia in nasal epithelium, concurrent with decreases of allergic Th2 cytokines and IL-17 in the draining lymph node. In conclusion, a novel PPARgamma ligand, KR62980, suppresses in vitro Th2 cell differentiation and attenuates in vivo OVA-induced airway inflammation, suggesting a beneficial role for KR62980 in the treatment of allergic asthma and allergic rhinitis.

Receptor tyrosine phosphatase, CD45 binds galectin-1 but does not mediate its apoptotic signal in T cell lines

Galectin-1 (Gal-1) is an endogenous mammalian S-type lectin with highly pleiotropic effect on different tissues. The viability of the lymphoid cells is reduced by gal-1 by triggering apoptosis, however, the mechanism of the gal-1 induced apoptosis is still under investigation. The receptor tyrosine phosphatase, CD45, a heavily glycosylated cell surface molecule binds to gal-1 with high affinity, however, its contribution to the gal-1 induced apoptosis is still controversial. In this study we show that galectin-1 binds to cells deficient for CD45, although CD45 is one of the galectin-1-binding cell surface proteins on T cells. Moreover, the CD45 deficient Jurkat variant, J45.01 responds readily with tyrosine phosphorylation and subsequent apoptosis to galectin-1 treatment in a similar degree as its wild type counterpart, Jurkat does. These results strongly indicate that CD45 is not the receptor via gal-1 mediates the apoptotic signal into the cells as it was suggested in previous studies.

Microheterogeneity of the cell surface tyrosine phosphatase, CD45RA, on T cells: phytohaemagglutinin binding and non-binding fraction of the 220 kDa isoform

The CD45 antigen is a family of the transmembrane tyrosine phosphatases expressed on cells of haemopoietic origin. The molecules are distinguished by the different aminoacid sequence and glycosylation on the N terminus. Although all isoforms are heavily glycosylated and exert receptor like structures on the extracellular part, the role of the glycosylation in the possible receptor function and the ligand of the CD45 has not been determined yet. In this study we have examined the binding of phytohaemagglutinin (PHA) to the different isoforms and its relation to the phosphatase activity. Immunoblotting experiments revealed that the 220 kDa form of the CD45RA contained a PHA binding fraction when immunoprecipitated with CD45RA monoclonal antibody (mAb), while an isoform with identical molecular mass immunoprecipitated by anti-CD45 did not bind PHA. We concluded that the 220 kDa form was heterogeneous with respect to PHA binding. Functional data also confirmed this heterogeneity: previous extraction of the PHA binding proteins resulted in the elimination of all the phosphatase activity from CD45, while only a part of that was removed from CD45RA immunoprecipitates.

The role of CD45 and CD45-associated molecules in T cell activation

CD45 (lymphocyte common antigen) is a receptor-linked protein tyrosine phosphatase that is expressed on all leucocytes, and which plays a crucial role in the function of these cells. On T cells the extracellular domain of CD45 is expressed in several different isoforms, and the particular isoform(s) expressed depends on the particular subpopulation of cell, their state of maturation, and whether or not they have previously been exposed to antigen. It has been established that the expression of CD45 is essential for the activation of T cells via the TCR, and that different CD45 isoforms display a different ability to support T cell activation. Although the tyrosine phosphatase activity of the intracellular region of CD45 has been shown to be crucial for supporting signal transduction from the TCR, the nature of the ligands for the different isoforms of CD45 have been elusive. Moreover, the precise mechanism by which potential ligands may regulate CD45 function is unclear. Interestingly, in T cells CD45 has been shown to associate with numerous molecules, both membrane associated and intracellular; these include components of the TCR-CD3 complex and CD4/CD8. In addition, CD45 is reported to associate with several intracellular protein tyrosine kinases including p56lck and p59fyn of the src family, and ZAP-70 of the Syk family, and with numerous proteins of 29-34 kDa. These CD45-associated molecules may play an important role in regulating CD45 tyrosine phosphatase activity and function. However, although the role of some of the CD45-associated molecules (e.g. CD45-AP and LPAP) has become better understood in recent years, the role of others still remains obscure. This review aims to summarize recent findings on the role of CD45 and CD45-associated molecules in T cell activation, and to highlight issues that seem relevant to ongoing research in this area.

CD26 expression correlates with entry, replication and cytopathicity of monocytotropic HIV-1 strains in a T-cell line

Experiments to identify cell determinants involved in HIV-1 tropism revealed a specific decrease in the expression of the T-cell activation antigen CD26 after monocytotropic (M-tropic) but not T-cell line-tropic (T-tropic) virus infection of the PM1 T-cell line. The level of CD26 expression in single-cell clones of PM1 correlated with the entry rate and cytopathicity of M-tropic HIV-1 variants, resulting in preferential survival of cells with low CD26 levels after infection. Experiments with recombinant viruses showed that the third hypervariable region of the envelope gp120 plays an important role in this selection process. This study identifies CD26 as a key marker for M-tropic human immunodeficiency virus type 1 (HIV-1) infection and suggests a mechanism for the early loss of CD26-expressing cells in HIV-1-infected individuals.

Changes in CD45 isoform expression vary according to the duration of T-cell memory after vaccination

Healthy young (< 40 years) and elderly (< 60 years) adults were immunized with the 1992-1993 preparation of trivalent influenza vaccine, and changes in CD45 isoform expression on peripheral blood lymphocytes were measured in the pre- and postvaccination periods. Fluorescence-activated cell sorter analysis was used to study T-cell subsets in fresh peripheral blood lymphocytes (day 0) and after 6 days of culture with live influenza virus. We have reported previously that the interleukin-2 response to the stimulating strain of virus, A/Texas/16/89, did not decline until 26 weeks postvaccination. In ex vivo CD4+ subsets, this interleukin-2 response was paralleled by a > 10% increase in the proportion of cells expressing the CD45RO+ phenotype following vaccination (p < 0.0001). In vitro stimulation had no effect on CD4+ subsets prior to vaccination but, after vaccination, was associated with a > 10% increase in CD45RA+RO+ cells (P < 0.0001). In addition, we have identified a change in the population of cells that express a CD45 isoform that is neither CD45RA nor CD45RO (CD45RA-RO-). At 26 weeks postvaccination, the proportion of CD45RA-RO- cells in ex vivo CD4+ peripheral blood mononuclear cells increased by approximately 15% from that measured at the earlier postvaccination time points (P < 0.0001). In vitro stimulation with influenza virus resulted in a further 20% increase in the proportion of CD45RA-RO- cells (P < 0.0001). The CD45RA-RO- phenotype may identify a population of cells undergoing apoptosis (programmed cell death) that limits the duration of helper T-cell (CD4+) memory after vaccination.

Effect of phytohaemagglutinin on CD45 in T cells

In this study the effect of PHA activation on the phosphatase activity of CD45 has been investigated in human leukemic T-cell lines. It has been found that in vivo activation of the cells with PHA resulted in 2-4-fold increase in enzyme activity. Addition of PHA to the postnuclear supernatant of cell lysates also resulted in elevation of phosphatase activity. Elevation of enzyme activity resulted from an increase in the amount of antigen in the immunoprecipitates. Elevation of the quantity was not the result of a de novo protein synthesis since the presence of cycloheximide, a protein synthesis inhibitor, did not modulate the effect of PHA. The effect of PHA was specific since ConA, that also bound to the CD45 molecules, or crosslinking of the antigen by antibody did not affect CD45. Since direct binding of PHA to CD45 molecules was shown in immunoblotting analysis, we suggest that the effect of PHA is a consequence of a PHA-induced conformational change of CD45 that results in up-regulation of the analyzed CD45 epitopes.

Anti-CD45 augments response of a Th2 clone to TCR cross-linking

The CD45 molecule is a transmembrane tyrosine phosphatase that may be associated with the T-cell receptor (TCR). This has led to the suggestion that CD45 may be important for the regulation of signal transduction in T cells. This idea is supported by the finding that antibodies against CD45 are comitogenic in proliferation assays. In the present work, we have examined the comitogenicity of CD45 antibodies by studying the effect of CD45, CD45RA, and CD45RB monoclonal antibodies (MoAbs) on proliferation of D10 cells induced with T-cell receptor (TCR) MoAbs. In addition interactions with some other proliferation inducing agents namely CD3 antibodies, lectins, and IL-2, are examined here. We have found that in general the CD45 MoAbs would significantly enhance proliferation induced by a wide spectrum of TCR MoAbs and other proliferation inducing agents, with some minor quantitative differences. The CD45 and CD45RB MoAbs were equally potent in their comitogenic activity while the CD45RA antibody was somewhat less potent. The comitogenic effect was maximal when CD45 antibodies were added simultaneously with the TCR MoAb, but significant comitogenicity could be detected when CD45 MoAbs were added up to 24 h after the initiation of the culture indicating that the CD45 antibodies also affect other processes than the initial signal transduction cascade.

Costimulatory properties of the human CD4 molecule: enhancement of CD3-induced T cell activation by human immunodeficiency virus type 1 through viral envelope glycoprotein gp120

This study was designed to investigate the T cell costimulatory activity of ligands binding to different regions on the human CD4 molecule. We assayed the costimulatory properties of a panel of CD4 MAbs, intact HIV, and viral envelope glycoproteins in CD3-induced activation of resting T cell subpopulations. Our data using MAbs reveal epitope-specific variations in the functional activities of CD4 MAbs under specific conditions in which CD3 and CD4 molecules are co-cross-linked. We show that both naive and memory CD4+ T cell subsets are susceptible to CD4-mediated costimulation, which overcomes the functional differences between the two cell populations in responsiveness to CD3 MAbs. We show for the first time that, analogous to CD4 MAbs, preparations of HIV and viral envelope glycoprotein gp120 are also potent costimulators of T cell proliferation and IL-2 production. On the basis of these results we propose possible mechanisms for polyclonal cell activation in the course of HIV infection and suggest that viral inhibitory and costimulatory effects may together disrupt the normal balanced function of the immune system, leading to AIDS.

Changes in CD45 isoform expression after influenza vaccination

In this study, we report the changes in the isoforms of CD45 expressed on T lymphocytes after influenza vaccination. Young adults were compared to an elderly group (26 participants/group) after vaccination with influenza split-virus vaccine. Peripheral blood mononuclear cells (PBMC) obtained pre-vaccination and 6 and 12 weeks post-vaccination were cultured with live influenza virus. Unstimulated and stimulated (5-day culture with virus) PBMC were labelled with fluorescent monoclonal antibody markers for CD3, CD4, CD8, CD45RA and CD45RO. When compared to the young controls, the elderly group had a higher proportion of CD45RO+RA- and, reciprocally, a lower proportion of CD45RA+RO- cells. In spite of these differences, both groups showed a progressive increase in the proportion of CD45RA+ T lymphocytes (CD4+ and CD8+) following influenza vaccination. In vitro stimulation with influenza virus resulted in a decrease in the proportion of CD45RA+RO- with a concomitant increase in the CD45RA-RO- population, both of which were observed only at 6 weeks post-vaccination. Although the phenotype of classical memory cells for recall antigen is CD45RO+, these results suggest that memory for influenza split-virus vaccine, exists in the CD45RO- population. More importantly, it should be noted that in spite of the decline in CD45RA+ cells with aging, the elderly group showed similar changes in the proportions of all cell phenotypes in response to vaccination, and to subsequent in vitro re-exposure to the virus.

Transmembrane signalling in T cells

Transmembrane signalling to activate T cells to proliferate and differentiate is a complex multistep process. It is the focus of much current interest, mostly because a selective and well-controlled inhibition of the process will allow regulation, or at least modulation, of the immune response. Here, Sándor Damjanovich and colleagues review the contributions of Hungarian scientists to the understanding of signalling in lymphocytes in particular, and cell activation in general.