Expression of interleukin-2 receptor gamma on human monocytes: characterization of lineage specific post-translational modifications

Characterization of IL-4 receptor components expressed on monocytes and monocyte-derived macrophages: variation associated with differential signaling by IL-4

The anti-inflammatory effects of IL-4 on activated monocytes differ from those on monocyte-derived macrophages (MDMac). While IL-4 suppresses LPS-induced IL-1beta , IL-12, IL-10 and TNFalpha production by monocytes, IL-4 suppresses only IL-1beta and IL-12 production by MDMac. The U937 and Mono Mac 6 cell lines have similar cytokine responses to IL-4 as monocytes and MDMac, respectively. The IL-4Ralpha and IL-2Rgamma (gammac) chains are well-characterized components of the IL-4 receptor. Cross-linking studies with 125I-IL-4 revealed that for monocytes and U937 cells, the binding of IL-4 to the receptor components was approximately 1:1 for IL-4Ralpha:gammac. In contrast, for MDMac and Mono Mac 6 cells that have a relative reduction in gammac surface expression, the binding of IL-4 to IL-4Ralpha:gammac was approximately 3:1. Furthermore, IL-4 induced IL-4Ralpha chain phosphorylation more rapidly in MDMac and Mono Mac 6 cells than in monocytes and U937 cells. This study identifies a correlation between altered 125I-IL-4 cross-linking to IL-4Ralpha:gammac, IL-4-induced signaling and regulation of pro-inflammatory cytokine production by IL-4.

Biology of the interleukin-2 receptor

Studies of the biology of the IL-2 receptor have played a major part in establishing several of the fundamental principles that govern our current understanding of immunology. Chief among these is the contribution made by lymphokines to regulation of the interactions among vast numbers of lymphocytes, comprising a number of functionally distinct lineages. These soluble mediators likely act locally, within the context of the microanatomic organization of the primary and secondary lymphoid organs, where, in combination with signals generated by direct membrane-membrane interactions, a wide spectrum of cell fate decisions is influenced. The properties of IL-2 as a T-cell growth factor spawned the view that IL-2 worked in vivo to promote clonal T-cell expansion during immune responses. Over time, this singular view has suffered from increasing appreciation that the biologic effects of IL-2R signals are much more complex than simply mediating T-cell growth: depending on the set of conditions, IL-2R signals may also promote cell survival, effector function, and apoptosis. These sometimes contradictory effects underscore the fact that a diversity of intracellular signaling pathways are potentially activated by IL-2R. Furthermore, cell fate decisions are based on the integration of multiple signals received by a lymphocyte from the environment; IL-2R signals can thus be regarded as one input to this integration process. In part because IL-2 was first identified as a T-cell growth factor, the major focus of investigation in IL-R2 signaling has been on the mechanism of mitogenic effects in cultured cell lines. Three critical events have been identified in the generation of the IL-2R signal for cell cycle progression, including heterodimerization of the cytoplasmic domains of the IL-2R beta and gamma(c) chains, activation of the tyrosine kinase Jak3, and phosphorylation of tyrosine residues on the IL-2R beta chain. These proximal events led to the creation of an activated receptor complex, to which various cytoplasmic signaling molecules are recruited and become substrates for regulatory enzymes (especially tyrosine kinases) that are associated with the receptor. One intriguing outcome of the IL-2R signaling studies performed in cell lines is the apparent functional redundancy of the A and H regions of IL-2R beta, and their corresponding downstream pathways, with respect to the proliferative response. Why should the receptor complex induce cell proliferation through more than one mechanism or pathway? One possibility is that this redundancy is an unusual property of cultured cell lines and that primary lymphocytes require signals from both the A and the H regions of IL-2R beta for optimal proliferative responses in vivo. An alternative possibility is that the A and H regions of IL-2R beta are only redundant with respect to proliferation and that each region plays a unique and essential role in regulating other aspects of lymphocyte physiology. As examples, the A or H region could prove to be important for regulating the sensitivity of lymphocytes to AICD or for promoting the development of NK cells. These issues may be resolved by reconstituting IL-2R beta-/-mice with A-and H-deleted forms of the receptor chain and analyzing the effect on lymphocyte development and function in vivo. In addition to the redundant nature of the A and H regions, there remains a large number of biochemical activities mediated by the IL-2R for which no clear physiological role has been identified. Therefore, the circumstances are ripe for discovering new connections between molecular signaling events activated by the IL-2R and the regulation of immune physiology. Translating biochemical studies of Il-2R function into an understanding of how these signals regulate the immune system has been facilitated by the identification of natural mutations in IL-2R components in humans with immunodeficiency and by the generation of mice with targeted mutations in these gen

Involvement of the IL-2 Receptor γ-Chain (γc) in the Control by IL-4 of Human Monocyte and Macrophage Proinflammatory Mediator Production

IL-4 has potent anti-inflammatory properties on monocytes and suppresses both IL-1β and TNF-α production. Well-characterized components of the IL-4 receptor on monocytes include the 140-kDa α-chain and the IL-2R γ-chain, γc, which normally dimerize 1:1 for signaling from the receptor. However, mRNA levels for γc were very low in 7-day-cultured monocytes. As mRNA levels for γc declined with culture, so too did the ability of IL-4 to down-regulate LPS-induced TNF-α production. In contrast, IL-4 consistently down-regulated IL-1β production by cultured monocytes. Immunoprecipitation and Western blot analyses demonstrated that 7-day-cultured monocytes do not express the functionally active 64-kDa γc protein. This was associated with decreased STAT6 activation by IL-4. Studies with Abs to γc and an IL-4 mutant that is unable to bind to γc showed that IL-4 can suppress IL-1β but not TNF-α production by LPS-stimulated monocytes in the presence of little or no functioning γc. IL-4 also suppressed IL-1β but not TNF-α production by Mono Mac 6 cells, which express minimal levels of γc. For γc-expressing LPS/PMA-activated U937 cells, IL-4 decreased both TNF-α and IL-1β production. These results suggest that functional γc is not present on in vitro-derived macrophages, and that while some anti-inflammatory responses to IL-4 are lost with this down-regulation of functional γc, others are retained. We conclude that different functional responses to IL-4 by human monocytes and macrophages are regulated by different IL-4 receptor configurations.

Further Analysis of Interleukin-2 Receptor Subunit Expression on the Different Human Peripheral Blood Mononuclear Cell Subsets

We have investigated the expression of the three components of the interleukin-2 receptor (IL-2Rα, IL-2Rβ, and IL-2Rγ) on the surface of the various peripheral blood mononuclear cell (PBMC) subsets by flow cytometry analysis. The PBMC were immediately isolated (ficoll) from blood collected on heparin as anticoagulant. The three IL-2R components are absent or only marginally detectable on CD4 T lymphocytes. No expression of the IL-2R chains is found for the B lymphocytes. In most donors, the three chains are not detectable on CD8 T lymphocytes, but for a few of them, IL-2Rβ or IL-2Rγ are clearly expressed. CD56 high (IL-2Rα+) and CD56 low (IL-2Rα−) natural killer (NK) cells express IL-2Rβ, but not IL-2Rγ. IL-2Rγ is expressed by monocytes of all donors although with variable intensity. When blood is collected on other anticoagulants or when cells are isolated 1 day after collection, IL-2Rα, IL-2Rβ, and IL-2Rγ are largely expressed on the surface of most PBMC. This observation provides a possible explanation for divergent data previously reported on IL-2R expression. Finally, we show that IL-2Rγ, which is not detectable on the cell surface of lymphocytes, is nevertheless expressed and stored as an intracellular component. This result is in agreement with the constitutive expression of the IL-2Rγ gene and suggests a specific regulatory mechanism for IL-2Rγ membrane translocation.

Further Analysis of Interleukin-2 Receptor Subunit Expression on the Different Human Peripheral Blood Mononuclear Cell Subsets

We have investigated the expression of the three components of the interleukin-2 receptor (IL-2Rα, IL-2Rβ, and IL-2Rγ) on the surface of the various peripheral blood mononuclear cell (PBMC) subsets by flow cytometry analysis. The PBMC were immediately isolated (ficoll) from blood collected on heparin as anticoagulant. The three IL-2R components are absent or only marginally detectable on CD4 T lymphocytes. No expression of the IL-2R chains is found for the B lymphocytes. In most donors, the three chains are not detectable on CD8 T lymphocytes, but for a few of them, IL-2Rβ or IL-2Rγ are clearly expressed. CD56 high (IL-2Rα+) and CD56 low (IL-2Rα−) natural killer (NK) cells express IL-2Rβ, but not IL-2Rγ. IL-2Rγ is expressed by monocytes of all donors although with variable intensity. When blood is collected on other anticoagulants or when cells are isolated 1 day after collection, IL-2Rα, IL-2Rβ, and IL-2Rγ are largely expressed on the surface of most PBMC. This observation provides a possible explanation for divergent data previously reported on IL-2R expression. Finally, we show that IL-2Rγ, which is not detectable on the cell surface of lymphocytes, is nevertheless expressed and stored as an intracellular component. This result is in agreement with the constitutive expression of the IL-2Rγ gene and suggests a specific regulatory mechanism for IL-2Rγ membrane translocation.

Functional cleavage of the common cytokine receptor gamma chain (gammac) by calpain

The small subunit of calpain, a calcium-dependent cysteine protease, was found to interact with the cytoplasmic domain of the common cytokine receptor gamma chain (gammac) in a yeast two-hybrid interaction trap assay. This interaction was functional as demonstrated by the ability of calpain to cleave in vitro-translated wild-type gammac, but not gammac containing a mutation in the PEST (proline, glutamate, serine, and threonine) sequence in its cytoplasmic domain, as well as by the ability of endogenous calpain to mediate cleavage of gammac in a calcium-dependent fashion. In T cell receptor-stimulated murine thymocytes, calpain inhibitors decreased cleavage of gammac. Moreover, in single positive CD4(+) thymocytes, not only did a calpain inhibitor augment CD3-induced proliferation, but antibodies to gammac blocked this effect. Finally, treatment of cells with ionomycin could inhibit interleukin 2-induced STAT protein activation, but this inhibition could be reversed by calpain inhibitors. Together, these data suggest that calpain-mediated cleavage of gammac represents a mechanism by which gammac-dependent signaling can be controlled.

Cloning and chromosomal mapping of bovine interleukin-2 receptor gamma gene

Interleukin-2 receptor (IL-2R) gamma chain, a member of the cytokine receptor superfamily, forms a high-affinity receptor with IL-2R alpha and beta chains that plays an important role in interleukin-2 (IL-2) signal transduction. We have cloned and characterized the bovine IL-2Rgamma gene and corresponding cDNA. Bovine IL-2Rgamma is a single-copy gene that contains 8 exons and spans approximately 3.8 kb. The promoter region lacks conventional TATA and CCAAT consensus sites, but contains several regulatory elements that are recognition sites for the GATA binding proteins, AP-1 and AP-2. Physical assignment by fluorescence in situ hybridization (FISH) placed the bovine IL-2Rgamma gene on chromosome Xq23.

Expression of the common cytokine receptor gamma chain by murine dendritic cells including epidermal Langerhans cells

The common cytokine receptor gamma chain (gamma c) is an indispensable component of interleukin (IL)-2, IL-4, IL-7, IL-9, and IL-15 receptors, and its expression has been detected in several leukocyte populations, including T cells, B cells, monocytes, natural killer cells, and neutrophils. The purpose of this study was to determine whether gamma c receptors are expressed by dendritic cells (DC). Constitutive gamma c mRNA expression was observed by reverse transcription polymerase chain reaction and/or Northern blotting for: (a) Ia+ epidermal Langerhans cells (LC), (b) 4F7+ splenic DC, (c) granulocyte/macrophage colony-stimulated factor-propagated bone marrow-derived DC, and (d) the epidermal-derived DC line, XS52, which retains important functions of epidermal LC. Exposure of XS52 cells to recombinant IL-4 induced a rapid up-regulation of c-myc mRNA expression, and this IL-4-dependent signaling was blocked almost completely by anti-gamma c monoclonal antibody (mAb) TUGm2 in a soluble form. Moreover, c-myc up-regulation was inducible in XS52 cells by the same mAb in an immobilized form. These results imply that molecules recognized by this antibody (i.e. gamma c receptors) are expressed on XS52 cell surfaces. We thus conclude that DC express functional gamma c receptors, which then mediate cytokine-dependent regulation of DC functions.

The role of shared receptor motifs and common Stat proteins in the generation of cytokine pleiotropy and redundancy by IL-2, IL-4, IL-7, IL-13, and IL-15

To understand the molecular bases for cytokine redundancy and pleiotropy, we have compared the Stat proteins activated in peripheral blood lymphocytes (PBLs) by cytokines with shared and distinct actions. Interleukin-2 (IL-2) rapidly activated Stat5 in fresh PBL, and Stat3 and Stat5 in preactivated PBL. IL-7 and IL-15 induced the same complexes as IL-2, a feature explained by the existence of similar tyrosine-phosphorylated motifs in the cytoplasmic domains of IL-2R beta and IL-7R that can serve as docking sites for Stat proteins. IL-13 Induced the same complexes as IL-4, a finding explained by our studies implicating IL-4R as a shared component of the receptors. These studies demonstrate that a single cytokine can activate different combinations of Stat proteins under different physiological conditions, and also indicate two mechanisms by which distinct cytokines can activate the same Stat protein.