Ramzi S. Cotran

Interleukin 1 acts on cultured human vascular endothelium to increase the adhesion of polymorphonuclear leukocytes, monocytes, and related leukocyte cell lines.

Increased leukocyte adhesion to the endothelial lining of blood vessels is an essential event in inflammation and the pathogenesis of certain vascular diseases. We have studied the effect of interleukin 1 (IL-1), an inflammatory/immune mediator, on endothelial-leukocyte adhesion using quantitative in vitro assays. Selective pretreatment of cultured human umbilical vein endothelial monolayers with IL-1 (5 U/ml, 4 h) resulted in an 18.3 +/- 2.6-fold increase in human peripheral blood polymorphonuclear leukocyte (PMN) adhesion (mean +/- SEM, n = 16) and a 2.6 +/- 0.3-fold increase in monocyte adhesion (n = 7) over basal levels. IL-1-treated endothelial monolayers also supported increased adhesion of the promyelocytic cell line HL-60 and the monocytelike cell line U937 (33.0 +/- 6.0-fold, n = 6 and 4.9 +/- 0.5-fold, n = 15, respectively). In contrast, selective IL-1 pretreatment of leukocytes, or the addition of IL-1 during the adhesion assay, did not alter endothelial-leukocyte adhesion. Conditioned medium from IL-1-treated endothelial cultures also did not promote leukocyte adhesion to untreated monolayers. IL-1 induction of endothelial adhesivity was concentration dependent (maximum, 10 U/ml), time dependent (peak, 4-6 h), and reversible, was blocked by cycloheximide (10 micrograms/ml) or actinomycin D (5 micrograms/ml) but not by acetylsalicylic acid (100 microM), and occurred without detectable endothelial cell damage. IL-1 treatment of SV40-transformed human endothelial cells and dermal fibroblasts did not increase their adhesivity for leukocytes. These data suggest that IL-1 can act selectively on human vascular endothelium to increase its adhesivity for circulating blood leukocytes, and thus to localize leukocyte-vessel wall interactions at sites of inflammation in vivo.

CD2AP Localizes to the Slit Diaphragm and Binds to Nephrin via a Novel C-Terminal Domain

CD2AP, an adapter protein containing multiple SH3 domains, plays a critical role in kidney function. Mice lacking CD2AP die soon after birth because of kidney failure. In the kidney, CD2AP is expressed in glomerular podocytes, which suggests that it may play a role in a specialized adhesion complex known as the slit diaphragm. One of the major components of the slit diaphragm is nephrin, a podocyte-specific protein. Here we demonstrate that CD2AP localizes to the slit diaphragm in podocytes using immunoelectron microscopy and that nephrin and CD2AP co-immunoprecipitate from a podocyte cell line. The specificity of this interaction was verified by mapping studies, which demonstrated that a novel domain at the C terminus of CD2AP interacts with the C-terminal portion of the nephrin cytoplasmic domain. These studies lend further support to the idea that CD2AP plays a role in the structural integrity of the slit diaphragm.

Immunologic interactions of T lymphocytes with vascular endothelium.

The data presented in this review establish that cultured human endothelial cells have the capacity to present antigens to T cells and to do so in the context of costimulators that lead to effective T cell activation. These activities raise the possibility that venular ECs, at sites of delayed hypersensitivity reactions, could be the primary antigen-presenting cell to circulating memory T cells. This putative role of ECs can explain the rapid rate of initiation of memory responses because ECs are uniquely positioned to have physical access to the pool of circulating memory T cells. Studies also suggest that ECs may present alloantigens to circulating T cells in the context of transplantation, thereby initiating rejection reactions. Nevertheless, we repeat our caveat that these proposed antigen-presenting functions of ECs have not been established in vivo. Cytokine-mediated changes, particularly induction of adhesion molecules and synthesis of lymphocyte-activating cytokines, such as IL-8, provide ECs with the potential to recruit memory T cells to inflammatory sites independent of antigen specificity. Although these functions have also not been rigorously shown to occur in vivo, immunocytochemical studies of experimental and pathological tissues provide significant support for this proposal. Similar adhesive and activating functions of ECs may apply to preferential homing of pre-T cells to thymus and naive T cells to lymph node. We conclude by noting that the weight of evidence reviewed here supports the proposal that the vascular endothelium be considered an integral part of the in vivo immune system.

The potential roles of vascular endothelium in immune reactions

Cell-mediated immune reactions are initiated and regulated by antigen specific CD4+ helper T cells. However, T cells cannot function independently. In order for a CD4+ T cell to recognize antigen, it must be presented in association with a class II major histocompatibility complex molecule by another cell type and, in order to lead to functional T-cell activation, the antigen presenting cell must also provide costimulatory signals. Once activated, CD4+ T cells function in vivo by secreting cytokines that elicit an inflammatory infiltrate of other cell types that serves to eliminate the source of foreign antigen. In vivo, the development of inflammation requires vascular responses as well as contributions of blood-derived leukocytes. Although several cell types in vitro can present antigen, provide costimulation, and perform actions that contribute to inflammation, vascular endothelial cells may be uniquely important immune accessory cells because they are anatomically uniquely positioned to function in vivo during cell-mediated immune reactions. In this report, we shall review recent data from our laboratories which further characterize the immune accessory functions of endothelial cells.

Macrophages and cellular immunity in experimental glomerulonephritis

We will consider in this review the evidence that monocytes directly contribute to glomerular injury as effector cells in some forms of glomerulonephritis, and that interactions between monocytes and lymphocytes-as a manifestation of cellular immunity-may, indeed, induce immune glomerular reactions. The review will focus primarily on experimental work, since clinical studies are discussed elsewhere in this book. A complex set of interactions between monocytes and lymphocytes underlies the expression of cellular immunity-which can be conveniently divided into two phases, an induction phase and an effector phase. The induction phase consists of specific lymphocyte recognition of an antigen presented on the membrane of a phagocytic cell. As the lymphocyte becomes activated, it releases factors that attract and activate monocytes. Activated phagocytic monocytes and macrophages, releasing degradative enzymes, toxic molecules, and factors that modulate differentiation and proliferation of other cell types, constitute the effector phase of cellular immunity [57]. The possible participation of monocytes, macrophages, and lymphocytes in the pathogenesis of glomerular injury has been considered for many years without resolution of the question. Recent morphologic and functional observations have demonstrated that mononuclear phagocytes play important roles as effector cells in certain models of immunologically induced glomerular injury. The association between infiltrating monocytes and glomerular damage has stimulated interest as to the induction mechanisms whereby monocytes are recruited into the glomerulus. One of the most interesting possibilities is that lymphocytes may cause the recruitment of effector monocytes. As yet, evidence in support of this mechanism is

Regulatory interactions of αβ and γλ T cells in glomerulonephritis

BACKGROUNDnSeveral lines of evidence suggest that cellular immune mechanisms contribute to glomerulonephritis.nnnMETHODSnThe roles of alphabeta and gammadelta T cells in the pathogenesis of glomerulonephritis were investigated in a model of nephrotoxic nephritis in mice deficient in either T-cell population [T-cell receptor (TCR)beta and TCRdelta knockout mice]. The model, induced by the injection of rabbit anti-mouse glomerular basement membrane antibody, is characterized by the development of proteinuria and glomerular damage over a 21-day observation period in wild-type mice.nnnRESULTSnMice deficient in either alphabeta or gammadelta T cells developed minimal proteinuria and glomerular lesions and had a significant reduction in macrophage accumulation compared with wild-type mice. In gammadelta T-cell-deficient mice, circulating levels and glomerular deposition of autologous IgG were comparable to wild-type levels, while alphabeta T-cell-deficient mice had no autologous IgG production. Autologous antibody production was not required for the development of glomerulonephritis since mice that lack IgG and B cells (micro-chain-/-) developed similar proteinuria to that observed in wild-type mice.nnnCONCLUSIONSnThese studies suggest a proinflammatory role for both alphabeta and gammadelta T cells in glomerular injury, independent of the humoral response. This is the first demonstration, to our knowledge, that both T-cell subsets contribute to the progression of a disease, and it suggests that complex regulatory interactions between alphabeta and gammadelta T cells play a role in glomerular injury.

Regulatory interactions of alphabeta and gammadelta T cells in glomerulonephritis.

BACKGROUNDnSeveral lines of evidence suggest that cellular immune mechanisms contribute to glomerulonephritis.nnnMETHODSnThe roles of alphabeta and gammadelta T cells in the pathogenesis of glomerulonephritis were investigated in a model of nephrotoxic nephritis in mice deficient in either T-cell population [T-cell receptor (TCR)beta and TCRdelta knockout mice]. The model, induced by the injection of rabbit anti-mouse glomerular basement membrane antibody, is characterized by the development of proteinuria and glomerular damage over a 21-day observation period in wild-type mice.nnnRESULTSnMice deficient in either alphabeta or gammadelta T cells developed minimal proteinuria and glomerular lesions and had a significant reduction in macrophage accumulation compared with wild-type mice. In gammadelta T-cell-deficient mice, circulating levels and glomerular deposition of autologous IgG were comparable to wild-type levels, while alphabeta T-cell-deficient mice had no autologous IgG production. Autologous antibody production was not required for the development of glomerulonephritis since mice that lack IgG and B cells (micro-chain-/-) developed similar proteinuria to that observed in wild-type mice.nnnCONCLUSIONSnThese studies suggest a proinflammatory role for both alphabeta and gammadelta T cells in glomerular injury, independent of the humoral response. This is the first demonstration, to our knowledge, that both T-cell subsets contribute to the progression of a disease, and it suggests that complex regulatory interactions between alphabeta and gammadelta T cells play a role in glomerular injury.

Effects of mononuclear phagocytes and their secretory products on vascular endothelium

There is increasing evidence that interactions between mononuclear phagocytes and vascular endothelium are involved in a variety of pathological processes. In its unique anatomic location, the endothelium could serve a regulatory role in the trafficking of blood monocytes across the vascular wall. Once localized at a particular site, monocytes and macrophages may potentially exert a broad spectrum of effects on vascular wall cells through the elaboration of biologically active products (Table I). In this paper we will first briefly review studies from our laboratory and others on the role of monocyte-macrophage-derived products which affect the growth of new blood vessels (neovascularization) and the proliferation of vascular smooth muscle cells and fibroblasts. We will then present results of current work on the induction of endothelial cell procoagulant activity (PCA) by human monocyte-derived interleukin 1 (IL-1). Finally, we will report certain recent observations on direct cellular interactions between mononuclear phagocytes and vascular endoxadthelium in vitro.

Current Concepts of Tubulointerstitial Nephritis

The purpose of this chapter is to summarize current views on the morphologic and clinical definition of interstitial nephritis, since many of the environmental agents, toxins, and drugs discussed in this book cause renal injury which affects primarily renal tubules and interstitium. It is generally agreed that a purely morphologic definition or classification of interstitial nephritis is of little value, since the histologic alterations are relatively nonspecific, and give little indication of etiology and pathogenesis. Rather, the terms interstitial nephritis or tubulointerstitial nephritis (or nephropathy) are used to describe a diverse group of renal disorders, caused by a variety of etiologic agents, in which the predominant morphologic involvement is in the tubules and the interstitium.