Stephen M. Denning

CD44 — A molecule involved in leukocyte adherence and T-cell activation

The study of cell surface molecules that are involved in interactions between immune and non-hematopoietic cells in various microenvironments is currently an area of great interest. One molecule that appears to be involved in multiple steps of normal immune cell function is now called CD44 and has been known previously as Pgp-1, In(Lu)-related p80, Hermes, ECM-III and HUTCH-I. Within the past year, the co-identity of all of these independently discovered molecules has become apparent, and the role of the CD44 molecule in T-cell activation has been discovered. In this review, Barton Haynes and his colleagues bring together numerous divergent lines of investigation on the CD44 molecule, review the many functional roles attributed to it, and present a unifying view of how, with numerous ligands, it may participate in several areas of normal immune cell function.

Ontogeny of T-cell precursors: a model for the initial stages of human T-cell development

Although most investigators agree that the CD4- CD8- CD3- thymocyte subset represents the most immature intrathymic T cell capable of repopulating the thymus in vivo, little is known of the earliest stages of human T-cell development. Using mAbs to hematopoietic and T-cell lineage molecules in quantitative immunofluorescence studies, new insight has been gained regarding the phenotype of human T-cell precursors before and after colonization of human thymic rudiment. In this article, Barton Haynes and colleagues discuss the sequential expression of CD7, CD4, CD8, CD3, CD2, CD1, CD45, TCR gamma delta and TCR alpha beta, and propose a model defining the stages of T-cell precursors during fetal ontogeny.

Characterization of human thymic epithelial cell surface antigens: Phenotypic similarity of thymic epithelial cells to epidermal keratinocytes

Cellular interactions between developing thymocytes and cells of the thymic microenvironment are necessary for maturation of thymocytes into mature T cells. While much is known about the molecules on developing T cells that mediate these interactions, little is known about the surface molecules of human thymic epithelial (TE) cells. In this study, using a panel of 276 MAb including 255 MAb from the 5th International Workshop on Human Leukocyte Differentiation Antigens (HLDA-V), we have determined the expression of CD1 through CDw130 and other surface molecules on resting and IFN-γ-activated cultured human TE cells and on resting epidermal keratinocytes (EK). We demonstrate the surface expression of 50 of the 161 molecules assayed for on TE cells, including a number of adhesion molecules, cytokine receptors,Apo-1, and MHC-encoded molecules. While activation of TE cells with IFN-γ for 48 hr induced a greater than fivefold increase in the expression of four surface molecules (CD38, CD54, MHC class I, and MHC class II), it also induced a greater than 50% increase in the expression of 14 other surface molecules (CD12, CD29, CD40, CD44, CD47, CD49b, CD49c, CD49e, CD55, CD66, CD87, CD104, TE4, and STE3) and a decrease in the expression of three molecules (CDw65, CDw109, and STE2). In comparing the phenotype of TE cells to 83 other cell lines studied in HLDA-V, we found that TE cells were strikingly more similar to EK than to any of the other cell types tested.

The role of leukocyte adhesion molecules in cellular interactions: implications for the pathogenesis of inflammatory synovitis.

Recently, considerable progress has been made in defining the molecules involved in interactions of hematopoietic cells with non-hematopoietic Cells of various microenvironments. While the events that lead to the initiation of the cascade of immunologic events eventuating in most types of human inflammatory synovitis such as rheumatoid arthritis (RA) are not known, it appears that there are both antigen-specific and antigen-independent phases of activation of cellular immune responses in synovitis. Although the specific antigens are not known that trigger T cell autoreactive responses in RA in humans, several animal models have been described in which a defined antigen of an infectious agent such as Mycoplasma arthriditis, triggers lymphocyte responses that lead to cell-mediated joint inflammation [51]. One cellular synovial immune response are triggered, both T and B lymphocytes as well as monocytes home to synovium by expressing organ-specific homing receptors that are involved in leukocyte binding to synovial microenvironment high endothelial venules (HEV) [5, 14, 20, 37, 38, 66, 79]. Homing lymphocytes and monocytes extravasate into the synovial tissue there interacting with a variety of cell types [9, 20, 37, 38, 43, 48, 75]. Lymphocyte and monocyte interactions with various cell types of the synovial microenvironment likely lead to amplification of all phases of T and B cell immune responses and also to the recruitment of additional leukocytes to inflammed synovium [7, 27, 41, 43, 75]. Other reports in this volume will deal in depth with specific adhesion molecules involved in lymphocyte-endothelial cell interactions (Ziff, pp 199-214; Jalkanen, pp 187-198 of this volume). In this report, we will review our recent research defining the distribution and function of select leukocyte adhesion molecules in synovium (Table 1), and present data regarding the roles that adhesion molecules might play in the pathogenesis of inflammatory synovitis.

Thymocytes and cultured thymic epithelial cells express transcripts encoding α-3, α-5 and β-4 subunits of neuronal nicotinic acetylcholine receptors: preferential transcription of the α-3 and β-4 genes by immature CD4+8+ thymocytes

Thymic tissues express transcripts encoding the alpha-3, alpha-5 and beta-4 subunits of nicotinic neuronal acetylcholine receptors (AcChRs) suggesting that neuronal AcChRs similar to those expressed in ganglia are expressed in the thymus. Transcription occurs in both isolated thymocytes and thymic epithelial cells. RT-PCR analyses of thymocyte subsets indicate that immature CD4 + 8 + thymocytes express higher levels of the alpha-3 and beta-4 transcripts than more mature thymocytes. Compared to freshly isolated thymocytes, peripheral blood lymphocytes do not express alpha-3 and beta-4 AcChR subunit transcripts. Cultured thymocytes rapidly down-regulate transcription of the alpha-3 and beta-4 AcChR subunit genes by a process that is not reversed by stimulation with phytohemagglutinin and IL-2. Thus our results indicate that there is transcriptional regulation of neuronal AcChR subunit genes during the process of thymocyte maturation and that factors within the thymic microenvironment influence expression of the alpha-3 and beta-4 AcChR subunit genes by developing T cells.

NOVEL MECHANISMS OF BREQUINAR SODIUM IMMUNOSUPPRESSION ON T CELL ACTIVATION

Brequinar sodium (BQR) is a novel immunosuppressive agent that acts by inhibiting the activity of dihydroorotate dehydrogenase, the fourth enzyme in the de novo pyrimidine biosynthetic pathway. The activity of BQR as an immunosuppressive agent is believed to be inhibition of antigen-induced lymphocyte proliferation through inhibition of DNA and RNA synthesis. BQR, therefore, has a different mechanism of action than cyclosporine and may potentiate the immunosuppressive effects of cyclosporine. In this study, we determined the effect of BQR on peripheral blood mononuclear cell (PBMC) activation in a series of in vitro culture systems. In these studies, BQR inhibited PHA-stimulated activation in a dose-dependent fashion beginning at 10(-6) M. The immunosuppressive effect of BQR was similar in magnitude to cyclosporine. Proliferation assays suggested an additive immunosuppression by the combination of BQR and cyclosporine. Similar inhibition of CD2-stimulated or CD3-stimulated activation of PBMC was found. The mechanisms of action of BQR were complex. BQR inhibited interleukin 2 protein production in response to mitogen stimulation. Cell surface interleukin 2 receptor expression was inhibited by BQR. BQR inhibited cell cycle progression, preventing progression from G0/G1 into S and G2 + M phases. BQR had no effect on induction of transcripts for the interleukin 2 receptor, but markedly inhibited the production of transcripts for interleukin 2. Thus, our studies indicate that BQR exerts a potent immunosuppression on mitogen-induced PBMC activation through multiple mechanisms. Consequently, BQR may be an effective agent for immunosuppression in organ transplantation or inflammatory diseases.

INDO-MO study of long-range EPR couplings in aliphatic formate radicals

Abstract In aqueous solution at ca. 25°C, simple aliphatic formate radicals of formula ·C(X 1 )(X 2 )-O-CHO and ·C(X 1 )(X 2 )-C(X 3 )(X 4 )-O-CHO (where an (X-) group is an H- or a substituent such as a CH 3 -) are well known to generally display γ- and δ-CH formyl-proton couplings, the size of these couplings varying with the nature of the (X-) groups. The origin of this variation is probably that the nature of the (X-) groups tends to affect the (s- trans )-to-(s- cis ) conformational isomerization of a given radical. By means of a detailed INDO-MO study of the simplest examples, ·CH 2 -O-CHO ( 1 ) and ·CH 2 -CH 2 -O-CHO ( 2 ), of these two specified general radical formulas, carried out by considering all conceivable bond rotations, we have shown that the previously reported variation of these long-range couplings with the nature of the (X-) groups is reasonable; that the conformational dependence of the long-range couplings is in accordance with the W-plan bond arrangement; that the experimental long-range formyl-proton couplings in 1 and 2 are consistent with 1 and 2 existing predominantly in the s- trans conformation; and that the signs of these long-range couplings in 1 and 2 are probably positive.

CD3 δ and ϵ gene expression in CD3t-CD16+ natural killer cell clones derived from thymic precursors

Abstract To better understand the maturational stages during T-cell development, we studied the expression of CD3δ and CD3ϵ genes, as well as the presence of TCR gene rearrangements, within CD3 − CD16 + NK clones derived from thymic precursors in vitro. Northern blot analysis revealed that CD3 − CD16 + clones derived from CD7 + CD3 − CD4 − CD8 − (TN) thymocytes expressed transcripts for the CD3ϵ gene; however, no transcripts for the CD38 gene were detected. Importantly, both the CD3ϵ and CD3δ genes were expressed in TN thymocytes examined prior to cloning. A CD7 + CD8 + CD3 − CD4 − thymocyte population that makes up only 0.4% of the total thymocyte pool was also isolated from human thymus. We determined the maturation potential of this CD7 + CDS + CD3 − CD4 − population by limiting dilution cloning and found that 67% of the clones generated in vitro had a CD3 − CD16 + CD8 + phenotype. In contrast to the NK clones derived from TN precursors, most CD3 − CD16 + clones derived from CD7 + CD8 + CD3 − CD4 − thymocytes expressed transcripts for both CD3ϵ and CD3δ genes. Southern blot analysis of the NK clones derived from either thymic precursor population revealed no rearrangement of the TCR β or γ genes. These results demonstrate that the TN progenitor population and their CD3 − CD16 + progeny differ in their expression of the CD38 transcript and during in vitro culture there is loss of CD38 expression and acquisition of surface CD16 within these NK clones. Furthermore, the CD3 − CD16 + clones derived from TN versus CD7 + CD8 + CD3 − CD4 − thymocytes differed in their expression of the CD38 gene. The signaling events regulating the expression of the CD3 invariant chain genes within immature lymphoid progenitor cells may be important in determining their eventual maturation into T-cell and NK-cell lineages in vivo.

Collagen Subtypes III and IV Expression in Human Vein Graft Atherosclerosis

This study examined the expression of collagen subtypes III and IV in a series of freshly excised human venous coronary artery bypass grafts. The results of this study demonstrate that these collagen subtypes are differentially expressed in vein graft atherosclerosis.