CD45RA T-cell activation without proliferation by a partial agonist monoclonal antibody to beta1 integrin

ArtinM Mediates Murine T Cell Activation and Induces Cell Death in Jurkat Human Leukemic T Cells

The recognition of cell surface glycans by lectins may be critical for the innate and adaptive immune responses. ArtinM, a d-mannose-binding lectin from Artocarpus heterophyllus, activates antigen-presenting cells by recognizing TLR2 N-glycans and induces Th1 immunity. We recently demonstrated that ArtinM stimulated CD4⁺ T cells to produce proinflammatory cytokines. Here, we further studied the effects of ArtinM on adaptive immune cells. We showed that ArtinM activates murine CD4⁺ and CD8⁺ T cells, augmenting their positivity for CD25, CD69, and CD95 and showed higher interleukin (IL)-2 and interferon (IFN)-γ production. The CD4⁺ T cells exhibited increased T-bet expression in response to ArtinM, and IL-2 production by CD4⁺ and CD8⁺ T cells depended on the recognition of CD3εγ-chain glycans by ArtinM. The ArtinM effect on aberrantly-glycosylated neoplastic lymphocytes was studied in Jurkat T cells, in which ArtinM induced IL-2, IFN-γ, and IL-1β production, but decreased cell viability and growth. A higher frequency of AnnexinV- and propidium iodide-stained cells demonstrated the induction of Jurkat T cells apoptosis by ArtinM, and this apoptotic response was reduced by caspases and protein tyrosine kinase inhibitors. The ArtinM effects on murine T cells corroborated with the immunomodulatory property of lectin, whereas the promotion of Jurkat T cells apoptosis may reflect a potential applicability of ArtinM in novel strategies for treating lymphocytic leukemia.

CD25 and CD69 induction by α4β1 outside-in signalling requires TCR early signalling complex proteins

Distinct signalling pathways producing diverse cellular outcomes can utilize similar subsets of proteins. For example, proteins from the TCR (T-cell receptor) ESC (early signalling complex) are also involved in interferon-α receptor signalling. Defining the mechanism for how these proteins function within a given pathway is important in understanding the integration and communication of signalling networks with one another. We investigated the contributions of the TCR ESC proteins Lck (lymphocyte-specific kinase), ZAP-70 (ζ-chain-associated protein of 70 kDa), Vav1, SLP-76 [SH2 (Src homology 2)-domain-containing leukocyte protein of 76 kDa] and LAT (linker for activation of T-cells) to integrin outside-in signalling in human T-cells. Lck, ZAP-70, SLP-76, Vav1 and LAT were activated by α4β1 outside-in signalling, but in a manner different from TCR signalling. TCR stimulation recruits ESC proteins to activate the mitogen-activated protein kinase ERK (extracellular-signal-regulated kinase). α4β1 outside-in-mediated ERK activation did not require TCR ESC proteins. However, α4β1 outside-in signalling induced CD25 and co-stimulated CD69 and this was dependent on TCR ESC proteins. TCR and α4β1 outside-in signalling are integrated through the common use of TCR ESC proteins; however, these proteins display functionally distinct roles in these pathways. These novel insights into the cross-talk between integrin outside-in and TCR signalling pathways are highly relevant to the development of therapeutic strategies to overcome disease associated with T-cell deregulation.

Heparan sulfate modification of the transmembrane receptor CD47 is necessary for inhibition of T cell receptor signaling by thrombospondin-1

Cell surface proteoglycans on T cells contribute to retroviral infection, binding of chemokines and other proteins, and are necessary for some T cell responses to the matricellular glycoprotein thrombospondin-1. The major cell surface proteoglycans expressed by primary T cells and Jurkat T cells have an apparent M(r) > 200,000 and are modified with chondroitin sulfate and heparan sulfate chains. Thrombospondin-1 bound in a heparin-inhibitable manner to this proteoglycan and to a soluble form released into the medium. Based on mass spectrometry, knockdown, and immunochemical analyses, the proteoglycan contains two major core proteins as follows: amyloid precursor-like protein-2 (APLP2, apparent M(r) 230,000) and CD47 (apparent M(r) > 250,000). CD47 is a known thrombospondin-1 receptor but was not previously reported to be a proteoglycan. This proteoglycan isoform of CD47 is widely expressed on vascular cells. Mutagenesis identified glycosaminoglycan modification of CD47 at Ser(64) and Ser(79). Inhibition of T cell receptor signaling by thrombospondin-1 was lost in CD47-deficient T cells that express the proteoglycan isoform of APLP2, indicating that binding to APLP2 is not sufficient. Inhibition of CD69 induction was restored in CD47-deficient cells by re-expressing CD47 or an S79A mutant but not by the S64A mutant. Therefore, inhibition of T cell receptor signaling by thrombospondin-1 is mediated by CD47 and requires its modification at Ser(64).

Co-engagement of alpha(4)beta(1) integrin (VLA-4) and CD4 or CD8 is necessary to induce maximal Erk1/2 phosphorylation and cytokine production in human T cells

The alpha(4)beta(1) integrin VLA-4 (very-late activation antigen-4) and the lineage-specific CD4 and CD8 receptors have been proposed as putative co-stimulatory receptors on T cells. To assess the relative contribution of signaling through the TCR, CD28 and these accessory molecules, we activated human T cells using soluble antibodies recognizing all four of these T-cell receptor classes (CD3, CD28, CD4/CD8, and VLA-4), and we assessed the degree of activation using higher-order flow cytometry detecting intracellular Erk1/2 phosphorylation and production of IL-2 and IFN-gamma. We found that: (1) co-stimulation via CD4/CD8, in addition to CD28, is required for optimal T-cell activation; (2) VLA-4 binding consistently potentiates CD4(+) and CD8(+) T-cell activation; (3) augmentation of T-cell activation through VLA-4 binding is most pronounced following engagement of CD4/CD8. These results confirm that multiple signals, including VLA-4 engagement, are necessary for maximal T-cell activation beyond that induced via the TCR and CD28.

Activation requirements and responses to TLR ligands in human CD4+ T cells: comparison of two T cell isolation techniques

Direct regulation of T cell function by microbial ligands through Toll-like receptors (TLR) is an emerging area of T cell biology. Currently either immunomagnetic cell sorting (IMACS) or fluorescence-activated cell sorting (FACS), are utilized to isolate T-cell subsets for such studies. However, it is unknown to what extent differences in T cell purity between these isolation techniques influence T cell functional assays. We compared the purity, response to mitogen, activation requirements, and response to TLR ligands between human CD4(+) T cells isolated either by IMACS (IMACS-CD4(+)) or by IMACS followed by FACS (IMACS/FACS-CD4(+)). As expected, IMACS-CD4(+) were less pure than IMACS/FACS-CD4(+) (92.5%+/-1.4% versus 99.7%+/-0.2%, respectively). Consequently, IMACS-CD4(+) proliferated and produced cytokines in response to mitogen alone and had lower activation requirements compared to IMACS/FACS-CD4(+). In addition IMACS-CD4(+) but not IMACS/FACS-CD4(+) responses were upregulated by the TLR-4 ligand lipopolysaccharide (LPS). On the other hand, TLR-2 and TLR-5 engagement induced costimulation in both IMACS-CD4(+) and highly purified IMACS-/FACS-CD4(+). Altogether these results indicate that small differences in cell purity can significantly alter T cell responses to TLR ligands. This study stresses the importance of a stringent purification method when investigating the role of microbial ligands in T cell function.