Kay H. Singer

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.

Epidermal keratinocytes express the adhesion molecule intercellular adhesion molecule-1 in inflammatory dermatoses

Using indirect immunofluorescence assays on frozen tissue sections of skin from healthy subjects and subjects with inflammatory skin diseases, we found that intercellular adhesion molecule-1 (ICAM-1) was expressed in a cell surface pattern on epidermal keratinocytes at the site of lymphoid infiltration in cutaneous dermatoses. ICAM-1 was not expressed on epidermal keratinocytes in noninflamed skin. Its expression was not related solely to epidermal hyperproliferation, as hyperproliferative, tape-stripped epidermis did not express ICAM-1. We have reported previously that ICAM-1 expression on epidermal keratinocytes was upregulated by treatment with interferon gamma and that activated T lymphocytes bound to cultured epidermal keratinocytes in vitro by lymphocyte function associated-1 (LFA-1) molecules on T cells and ICAM-1 on epidermal keratinocytes. Taken together, these data suggest that upregulation of expression of ICAM-1 is an important feature of cutaneous inflammation.

In vitro growth and phenotypic characterization of mesodermal-derived and epithelial components of normal and abnormal human thymus

Long-term in vitro cultures of human thymic tissue were established and phenotypically characterized using monoclonal reagents that define distinct components of the human thymic microenvironment. The epithelial component of the thymus, defined by monoclonal antibodies TE-3, TE-4, BBTECS, and AE1 (anti-keratin) was isolated from the mesodermal component, defined by antibody TE-7, and maintained separately in long-term culture. The epithelial cells were subcultured repeatedly and recovered from storage in liquid nitrogen. The in vitro phenotype of the cultured cells was compared to that of cultured human epidermal cells. A subpopulation of cultured thymic epithelial cells along with a subpopulation of cultured epidermal cells expressed antigens (TE-8, TE-15) characteristic of late stages of keratinized epithelial cell differentiation. Thus, we have established a system whereby components of the human thymic microenvironment can be cultivated in vitro while maintaining the capacity to differentiate. This approach can be used to evaluate the role of components of the thymic microenvironment at various stages of differentiation on developing T lymphocytes. In addition, keratin-containing thymic epithelial cells were successfully cultured from thymuses obtained from patients with myasthenia gravis and thymoma. Cultivation of abnormal thymic epithelium will provide insight into aberrant T lymphocyte-thymic epithelial interaction.

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.

Correlation of epidermal plasminogen activator activity with disease activity in psoriasis

The specific activity of plasminogen activator was increased in clinically involved psoriatic epidermis compared with the uninvolved skin of the same eight patients. Alterations in plasminogen activator activity correlated with disease activity as measured by extent of body surface involved with psoriasis. Levels of plasminogen activator increased in uninvolved epidermis of psoriatic patients during retinoid therapy.

Interactions between epithelial cells and T lymphocytes: role of adhesion molecules.

Cell‐cell interaction is critical for normal T cell development and function. A number of adhesion molecules important in T cell interactions with other cell types have been defined. This paper reviews the role of two adhesion pathways, CD2/LFA‐3 and LFA‐1/ICAM‐1, in T cell interactions with epithelial cells of the thymus and skin. While thymic epithelium‐T cell interactions are mediated by both the LFA‐1/ICAM‐1 pathway and the CD2/LFA‐3 pathway, epidermal‐T cell interactions are mediated primarily by the LFA‐1/ICAM‐1 pathway. Although ICAM‐1 is not expressed in vivo on epidermal keratinocytes in normal skin, ICAM‐1 is expressed by epidermal keratinocytes at the site of T cell infiltration in inflammatory dermatitis. ICAM‐1 is expressed in vivo on thymic epithelium. These antigen independent adhesion molecules play an important role in the cell‐cell interactions associated with T cell differentiation and function.

Penicillamine-induced pemphigus. Immunoglobulin from this patient induces plasminogen activator synthesis by human epidermal cells in culture: mechanism for acantholysis in pemphigus

The incubation of cultured epidermal cells with IgG obtained from a 56-year-old man with penicillamine-induced pemphigus resulted in an increase in extracellular and intracellular plasminogen activator. This suggests that penicillamine-induced pemphigus and spontaneously occurring pemphigus share common pathophysiologic processes in the induction of blister formation.

Human thymic epithelial cells: adhesion molecules and cytokine production

SummaryThe ability to culture human thymic epithelial cells has greatly facilitated studies of direct cell-cell interaction between thymic epithelial cells and T lymphocytes in vitro, as well as cytokine production and regulation of cytokine production. In vitro, human thymic epithelial cells bind to T lymphocytes via two adhesion pathways: CD2-lymphocyte function-associated antigen-3 and lymphocyte function-associated antigen-1-intercellular adhesion molecule-1. Cultured human thymic epithelial cells produce interleukins-1α, −1β, −3, −6 and −8, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, leukemia inhibitory factor and transforming growth factor-α. Production of thymic epithelial cell-drived cytokines is regulated by both adhesion molecules (lymphocyte function-associated antigen-3) and soluble factors via both autocrine (interleukin-1α, transforming growth factor-α) and paracrine (interleukin-4, interferon-γ) pathways. Transforming growth factor-α and epidermal growth factor regulate various cytokine mRNA at a post-transcriptional level by increasing cytokine mRNA stability.

Epithelial-thymocyte interactions in human thymus.

Our data demonstrate that the epithelial component of the human thymic microenvironment is not an inert cell type, but rather is capable of being directly involved in the promotion of both early and late stages of T-cell maturation. Data from our laboratory [54,69], together with the work of Plunkett et al. [61] and Shaw et al. [70] suggest that an endogenous ligand for the CD2 molecule in humans is the LFA-3 molecule. Using an SV40 transformed human thymic epithelial cell line of subcapsular cortical origin, Mizutani et al. have confirmed that thymic epithelial cells bind thymocytes via a CD2/LFA-3 interaction [78]. The data reviewed in this paper suggest that within the thymus one endogenous ligand for the alternative pathway of thymocyte activation via the CD2 molecule is the LFA-3 molecule on TE cells. Following thymocyte binding to TE cells, immature thymocytes are directly activated to proliferate, and their response to both IL1 and IL2 is augmented. Also, following TE-thymocyte binding, TE-IL1 secretion is augmented and TE cell MHC class II antigen expression is induced. Moreover, while undergoing activation, thymocytes appear to be able to modulate their microenvironment milieu of MHC antigens and IL1. Further analysis of the sequelae of TE-thymocyte interactions using phenotypic characterization of thymocytes with anti-T-cell MoAbs, coupled with molecular analysis of thymocyte T-cell receptor genes, should allow for the determination of the precise sequential stages that immature T cells undergo enroute to functional maturity. Understanding these steps in T-cell maturation will be critical to our understanding of the events that transpire in the genesis of autoimmune, lymphoproliferative, and immunodeficiency diseases.

The effect of corticosteroids, dapsone and gold upon plasminogen activator synthesis and secretion by human epidermal cells cultured with pemphigus antibody

Human epidermal cells were cultured with pemphigus antibody in the presence of hydrocortisone, methlprednisolone sodium succinate, dapsone and gold. Hydrocortisone and methylprednisolone reduced the production of the enzyme plasminogen activator but dapsone and gold had no effect. These results support the hypothesis that corticosteroids have dual effects on pemphigus through inhibition of plasminogen activator production by epidermal cells and suppression of pemphigus antibody production by B lymphocytes.