The distribution of lymphocytes expressing alphabeta and gammadelta T-cell receptors, and the expression of mucosal addressin cell adhesion molecule-1 in the canine intestine

The present study defined the distribution of alphabeta and gammadelta T-cell subsets, and the expression of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) in the intestinal tract of an outbred population of dogs with no evidence of gastrointestinal disease. A panel of monoclonal antibodies reactive with the canine alphabeta and gammadelta T-cell receptors (TCRs) and human MAdCAM-1 was used in a series of immunoperoxidase or immunofluorescence studies. alphabeta T cells were predominant within the villous lamina propria with a significantly decreasing linear trend from upper villus to crypt (P<0.0001). A proportion of intraepithelial lymphocytes (IELs) also expressed the alphabeta T-cell receptor, with significantly greater numbers in villous than in crypt epithelium (P<0.0001). However, there were no significant differences in the numbers of either lamina propria or epithelial alphabeta T cells between different intestinal regions. gammadelta T cells were rare in the lamina propria, but a prominent gammadelta IEL population was present and shown by double-colour immunofluorescence studies to be principally of the CD4(&)minus;CD8alpha(&)minus; phenotype. MAdCAM-1 was expressed by endothelial cells in the mucosa, sub-mucosa and muscularis layers of all levels of the intestinal tract. In the mucosa, significantly more MAdCAM-1 positive endothelium was present in regions of crypt than villous lamina propria (P<0.0001), but there were no significant differences between expression in different intestinal regions. The quantitative and qualitative data will enable comparisons of these parameters to be made with those in dogs suffering from inflammatory bowel diseases.

Enhanced expression of eotaxin and CCR3 mRNA and protein in atopic asthma. Association with airway hyperresponsiveness and predominant co-localization of eotaxin mRNA to bronchial epithelial and endothelial cells

Eotaxin is a newly discovered C-C chemokine which preferentially attracts and activates eosinophil leukocytes by acting specifically on its receptor CCR3. The airway inflammation characteristic of asthma is believed to be, at least in part, the result of eosinophil-dependent tissue injury. This study was designed to determine whether there is increased expression of eotaxin and CCR3 in the bronchial mucosa of asthmatics and whether this is associated with disease severity. The major sources of eotaxin and CCR3 mRNA were determined by co-localization experiments. Bronchial mucosal biopsy samples were obtained from atopic asthmatics and normal non-atopic controls. Eotaxin and CCR3 mRNA were identified in tissue sections by in situ hybridization (ISH) using radiolabeled riboprobes and their protein product visualized by immunohistochemistry (IHC). Co-localization experiments were performed by double ISH/IHC. Eotaxin and CCR3 (mRNA and protein) were significantly elevated in atopic asthmatics compared with normal controls. In the asthmatics there was a highly significant inverse correlation between eotaxin mRNA+ cells and the histamine provocative concentration causing a 20% fall in FEV1 (PC20). Cytokeratin-positive epithelial cells and CD31+ endothelial cells were the major source of eotaxin mRNA whereas CCR3 co-localized predominantly to eosinophils. These data are consistent with the hypothesis that damage to the bronchial mucosa in asthma involves secretion of eotaxin by epithelial and endothelial cells resulting in eosinophil infiltration mediated via CCR3. Since selective (eotaxin) and non-selective C-C chemokines such as RANTES, MCP-3 and MCP-4 all stimulate eosinophils via CCR3, this receptor is potentially a prime therapeutic target in the spectrum of diseases involving eosinophil-mediated tissue damage.

Cellular localization of the chemokine receptor CCR5. Correlation to cellular targets of HIV-1 infection

The chemokine receptor CCR5 has recently been described as a co-receptor for macrophage-tropic strains of human immunodeficiency virus (HIV)-1. In this study, using a panel of monoclonal antibodies specific for human CCR5, we show by immunohistochemistry and flow cytometry that CCR5 is expressed by bone-marrow-derived cells known to be targets for HIV-1 infection, including a subpopulation of lymphocytes and monocyte/macrophages in blood, primary and secondary lymphoid organs, and noninflamed tissues. In the central nervous system, CCR5 is expressed on neurons, astrocytes, and microglia. In other tissues, CCR5 is expressed on epithelium, endothelium, vascular smooth muscle, and fibroblasts. Chronically inflamed tissues contain an increased number of CCR5+ mononuclear cells, and the number of immunoreactive cells is directly associated with a histopathological correlate of inflammatory severity. Collectively, these results suggest that CCR5+ cells are recruited to inflammatory sites and, as such, may facilitate transmission of macrophage-tropic strains of HIV-1.

Human mucosal addressin cell adhesion molecule-1 is preferentially expressed in intestinal tract and associated lymphoid tissue

Lymphocyte homing to normal tissues and recruitment to inflammatory tissue sites are controlled, in part, by the selective expression of chemokines, pro-inflammatory cytokines and mediators, and various adhesion proteins and molecules. In the mouse, mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is selectively expressed on endothelium of high endothelial venules in gut and gut-associated lymphoid tissue. By interaction with its integrin ligand, alpha 4 beta 7, lymphocytes presumed to be involved in mucosal immunity are selectively recruited to these intestinal sites. After generating monoclonal antibodies against a murine cell line expressing recombinant human MAdCAM-1, we qualitatively and semiquantitatively assessed MAdCAM-1 expression in human tissue sections from various normal and inflammatory disorders. We found that human MAdCAM-1, as in the mouse, is expressed in a tissue-selective manner. In normal tissues, MAdCAM-1 is constitutively expressed to endothelium of venules of intestinal lamina propria. Interestingly, using computer-assisted morphometric analysis, the proportion of venular endothelium within lamina propria that expresses MAdCAM-1 is increased, compared with normal tissues, at inflammatory foci associated with ulcerative colitis and Crohn's disease. Moreover, for the most part, MAdCAM-1 is not detected in the majority of normal or inflamed extra-intestinal tissues, including those with mucosal surfaces. These results are consistent with a role, as originally defined in the mouse, for human MAdCAM-1 in the localization of alpha 4 beta 7+ lymphocytes in the gastrointestinal tract and associated lymphoid tissue. As such, the pathway defined by MAdCAM-1/alpha 4 beta 7 may be a relevant tissue-specific therapeutic target for the modulation of inflammatory bowel disease activity.

Monoclonal antibodies specific for beta 7 integrin and mucosal addressin cell adhesion molecule-1 (MAdCAM-1) reduce inflammation in the colon of scid mice reconstituted with CD45RBhigh CD4+ T cells

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is an adhesion protein expressed on endothelium in mucosal tissues that has been shown to play an important role in the selective homing of lymphocytes to intestinal mucosa and associated lymphoid tissue. To determine whether MAdCAM-1 or its ligand alpha 4 beta 7 would be appropriate targets for therapeutic intervention in gut-associated inflammation, we tested the ability of rat mAbs specific for beta 7 integrin and MAdCAM-1 to inhibit chronic colonic inflammation in scid mice reconstituted with CD4+ T cells enriched for the CD45RBhigh subpopulation. Abs specific for beta 7 and MAdCAM-1 blocked recruitment of lymphocytes to the colitic colon, and more importantly, these Abs significantly reduced the severity of colonic inflammatory disease in this animal model. Therefore, the adhesive interactions mediated by alpha 4 beta 7 and MAdCAM are intimately involved in leukocyte recruitment to gut in chronic inflammatory disease and may be relevant therapeutic targets for patients with inflammatory bowel disease.

Monoclonal antibodies specific for beta 7 integrin and mucosal addressin cell adhesion molecule-1 (MAdCAM-1) reduce inflammation in the colon of scid mice reconstituted with CD45RBhigh CD4+ T cells

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is an adhesion protein expressed on endothelium in mucosal tissues that has been shown to play an important role in the selective homing of lymphocytes to intestinal mucosa and associated lymphoid tissue. To determine whether MAdCAM-1 or its ligand alpha 4 beta 7 would be appropriate targets for therapeutic intervention in gut-associated inflammation, we tested the ability of rat mAbs specific for beta 7 integrin and MAdCAM-1 to inhibit chronic colonic inflammation in scid mice reconstituted with CD4+ T cells enriched for the CD45RBhigh subpopulation. Abs specific for beta 7 and MAdCAM-1 blocked recruitment of lymphocytes to the colitic colon, and more importantly, these Abs significantly reduced the severity of colonic inflammatory disease in this animal model. Therefore, the adhesive interactions mediated by alpha 4 beta 7 and MAdCAM are intimately involved in leukocyte recruitment to gut in chronic inflammatory disease and may be relevant therapeutic targets for patients with inflammatory bowel disease.

Rapid resolution of chronic colitis in the cotton-top tamarin with an antibody to a gut-homing integrin alpha 4 beta 7

BACKGROUND & AIMS

Integrins play diverse roles in cellular actions and signalling in the immune system. In the context of mucosal immune responses, the integrin alpha 4 beta 7 has received particular attention because of its intimate involvement in lymphocyte recruitment to normal gastrointestinal mucosa and associated lymphoid tissue. The aim of this study was to determine the functional relevance of alpha 4 beta 7 in the pathogenesis of colonic inflammatory disease using the colitic cotton-top tamarin, an animal model of human ulcerative colitis.

METHODS

Chronically colitic cotton-top tamarins were given either a cross-reactive monoclonal antibody to human alpha 4 beta 7 or an irrelevant control monoclonal antibody. The animals were then evaluated clinically and mucosal biopsy specimens assessed by histological and quantitative morphometric analysis.

RESULTS

A blocking monoclonal antibody to alpha 4 beta 7 integrin ameliorated inflammatory activity and rapidly improved stool consistency when administered to chronically colitic animals. Furthermore, using morphometric analysis of biopsy specimens, antibody therapy reduced the mucosal density of alpha 4 beta 7+ lymphocytes and alpha 4 beta 7 neutrophils and macrophages.

CONCLUSIONS

These results suggest that the alpha 4 beta 7 integrin represents a novel, potentially organ-specific therapeutic target for the treatment of inflammatory bowel disease.

Chemokine expression in simian immunodeficiency virus-induced AIDS encephalitis

The pathogenesis of neurological dysfunction associated with human immunodeficiency (HIV)-1 infection is uncertain. However, the presence of macrophage infiltrates in the central nervous system is a key feature of HIV encephalitis and is correlated with HIV-associated dementia. Moreover, it has been demonstrated that HIV-infected monocyte/macrophages can produce toxic substances that may play a critical role in the development of HIV-associated dementia. However, the exact mechanisms responsible for HIV infection and leukocyte recruitment to the central nervous system remain speculative. Similar to HIV-infected patients, simian immunodeficiency virus (SIV)-infected macaque monkeys develop immunosuppression and acquired immune deficiency syndrome (AIDS)-related inflammatory disorders, including AIDS encephalitis. In this study, we demonstrate that encephalitic brain from SIV-infected animals has elevated immunohistochemical expression of the C-C chemokines, macrophage inflammatory protein-1 alpha and -beta, RANTES, and monocyte chemotactic protein-3, and the C-X-C chemokine interferon-inducible protein-10. These findings suggest that one or all of of these chemokines could be involved in leukocyte recruitment to the brain in SIV-infected macaque monkeys.

Phenotype, and migration properties of three major subsets of tissue homing T cells in sheep

T cells show a bias in their migration pathways: some T cells preferentially migrate to peripheral lymph nodes (LN), some to mucosal tissues, and some to peripheral tissues such as skin. These recirculation pathways were examined in sheep by collecting lymph draining into and out of peripheral and intestinal LN, and using fluorescent dyes to trace the recirculation of the lymph cells. Monoclonal antibodies (mAb) to alpha 4, beta 1, and beta 7 integrins, and L-selectin, were used to define three major populations of recirculating T cells. Naive-type T cells (L-selectin+, alpha 4 beta 1lo beta 7lo) migrated preferentially through peripheral LN. Two memory populations could be defined: alpha 4 beta 1hi beta 7- and alpha 4 beta 7hi beta 1lo. alpha 4 beta 1hi beta 7- T cells were present in lymph draining from the skin. T cells migrating preferentially through intestinal LN were alpha 4 beta 7hi beta 1lo. Consistent with this migration pattern, the endothelial receptor for alpha 4 beta 7, mucosal addressin cell adhesion molecule-1 (MAdCAM-1) was detected on high endothelial venules within intestinal LN and Peyer's patches, but only weakly on high endothelial venules within peripheral LN. Thus, there are at least three easily definable subsets of T cells, based on integrin expression, which show distinct migration preferences.

Peripheral blood eosinophilia in owl monkeys is associated with increased eosinophilopoiesis yet depressed recruitment kinetics to the Chemokine RANTES

New world nonhuman primates of the genus Aotus (owl monkeys) can be categorized by 11 distinct karyotypes (K). It has been demonstrated that monkeys of K-VI persistently have one order of magnitude more eosinophils (EOS) in the peripheral blood than K-I monkeys. The purpose of this study was to investigate the basis for this difference and examine EOS recruitment using two cutaneous models of inflammation. Peripheral blood EOS were isolated on metrizamide gradients to > or = 95% purity and then used for phenotypic studies. There were no significant differences when comparing karyotypes in the ratio of normodense (K-I, 6.4% +/- 3.8%; K-VI, 21.1% +/- 8.8%) EOS or their survival in culture (K-I, 5.3% +/- 2.9% at 72 hours; K-VI, 2.8% +/- 0.7% at 72 hours) (P > .05). Examination of bone marrow revealed that K-VI monkeys had greater than fivefold more EOS and EOS precursors than K-I animals. To examine EOS function in recruitment, monkeys of each karyotype were given a single intradermal injection of Escherichia coli lipopolysaccharide (LPS) or human recombinant (PMN) and mononuclear cells occurred in response to LPS as early as 4 hours after injection; the severity of infiltration was similar in both karyotypes and at all time points up to 24 hours. In contrast, by 8 hours after intradermal injection of RANTES, leukocyte infiltration in K-I monkeys consisted mostly of PMN (94.8% +/- 0.7%) that were predominantly EOS. In comparison, there was essentially no infiltrate in K-VI animals at all time points. There was no difference in VCAM-1 expression in response to intradermal LPS or RANTES between the two karyotypes. These results suggest that the genetic basis of peripheralblood eosinophilia in K-VI owl monkeys is likely a function of heightened eosinophilopoiesis and depressed recruitment kinetics from the peripheral circulatory pool in response to RANTES.

Inhibition of T cell recruitment and cutaneous delayed-type hypersensitivity-induced inflammation with antibodies to monocyte chemoattractant protein-1

Leukocytes express chemokine receptors that, upon ligand recognition, are believed to activate and induce the directed migration of these cells from the vasculature to sites of tissue injury. Previous investigations of human and animal inflammatory tissue have revealed that expression of chemokines can be increased in association with leukocyte infiltration. Monocyte chemotactic protein-1 (MCP-1) mediates monocyte chemotaxis in vitro and migration of monocytes to inflammatory sites in vivo. More recently T cell chemotaxis to MCP-1 has been observed in vitro, but the contribution of this protein to T cell migration in vivo and to lymphocyte-mediated inflammation has not been determined. In this report, we show that using a rat model of cutaneous delayed hypersensitivity, MCP-1 expression correlates spatially and kinetically with T cell and monocyte recruitment and that antibodies directed to MCP-1 when administered therapeutically to animals undergoing delayed hypersensitivity can almost completely abolish T cell migration and inflammatory sequelae. Moreover the concentration of antibody needed to inhibit T cell trafficking to inflammatory sites is almost on order of magnitude lower than that needed to impede monocyte recruitment. Therefore, MCP-1 is functionally relevant in the genesis of delayed hypersensitivity and may be a useful therapeutic target for diseases mediated in part by T lymphocytes.

Cloning of the human eosinophil chemoattractant, eotaxin. Expression, receptor binding, and functional properties suggest a mechanism for the selective recruitment of eosinophils

The CC chemokine eotaxin, identified in guinea pigs and also recently in mice, may be a key element for the selective recruitment of eosinophils to certain inflamed tissues. Using a partial mouse eotaxin CDNA probe, the human eotaxin gene was cloned and found to be 61.8 and 63.2% identical at the amino acid level to guinea pig and mouse eotaxin. Human eotaxin protein was a strong and specific eosinophil chemoattractant in vitro and was an effective eosinophil chemoattractant when injected into the skin of a rhesus monkey. Radiolabeled eotaxin was used to identify a high affinity receptor on eosinophils (0.52 nM Kd), expressed at 4.8 x 10(4) sites per cell. This receptor also bound RANTES and monocyte chemotactic protein-3 with lower affinity, but not macrophage inflammatory protein-1 alpha. Eotaxin could desensitize calcium responses of eosinophils to RANTES and monocyte chemotactic protein-3, although RANTES was able to only partially desensitize eosinophil calcium responses to eotaxin. Immunohistochemistry on human nasal polyp with antieotaxin mAbs showed that certain leukocytes as well as respiratory epithelium were intensely immunoreactive, and eosinophil infiltration occurred at sites of eotaxin upregulation. Thus eotaxin in humans is a potent and selective eosinophil chemoattractant that is expressed by a variety cell types in certain inflammatory conditions.

VCAM-1 expression and leukocyte trafficking to the CNS occur early in infection with pathogenic isolates of SIV

This study reports on the endothelial expression of vascular cell adhesion molecule-1 (VCAM-1) in the central nervous system (CNS) early after experimental infection of rhesus monkeys (Macaca mulatta) with pathogenic and nonpathogenic simian immunodeficiency virus (SIV). Diffuse endothelial expression of VCAM-1 was observed in the CNS in all animals receiving pathogenic SIV. These findings demonstrate the rapidity with which pathogenic SIV is able to enter the CNS and induce endothelial cell activation.

Monocyte-chemoattractant protein 1 gene expression in intestinal epithelial cells and inflammatory bowel disease mucosa

BACKGROUND

Monocyte-chemoattractant protein 1 (MCP-1) activates macrophages and increases the migration of monocytes into tissue during inflammation. It was hypothesized that MCP-1 expression is involved in intestinal inflammation.

METHODS

MCP-1 protein was detected by immunohistochemistry and immunoprecipitation. Biological activity of MCP-1 was assessed using a chemotactic assay. MCP-1 messenger RNA (mRNA) levels were measured by quantitative reverse-transcription polymerase chain reaction.

RESULTS

In normal mucosa, MCP-1 was predominantly present in surface epithelium. In contrast, inflamed mucosa from patients with ulcerative colitis or Crohn's disease contained multiple cells immunoreactive for MCP-1, including spindle cells, mononuclear cells, and endothelial cells. Furthermore, MCP-1 mRNA expression was markedly increased in inflamed intestinal biopsy specimens from patients with inflammatory bowel disease. MCP-1 was detected in isolated intestinal epithelial cells and in conditioned media from Caco-2 cells. Caco-2 cell-conditioned media stimulated monocyte chemotaxis activity that was inhibited by anti-MCP-1 antibodies. Constituitive MCP-1 mRNA levels in Caco-2 cells were up-regulated by interleukin 1 beta and down-regulated by dexamethasone.

CONCLUSIONS

In addition to lamina propria macrophages, endothelial cells, and spindle cells, intestinal epithelial cells are able to produce MCP-1. MCP-1 is expressed constitutively in the intestinal colonic mucosa and is up-regulated during inflammation.

Macrophage function in simian AIDS. Killing defects in vivo are independent of macrophage infection, associated with alterations in Th phenotype, and reversible with IFN-gamma

Infection of macrophages (M phi) in vitro with M phi-tropic isolates of simian immunodeficiency virus (SIV) did not affect killing of Cryptococcus neoformans up to 16 days after inoculation (p < 0.05). Conversely, alveolar M phi from animals with SIV-induced AIDS killed C. neoformans less efficiently (10.4 +/- 2.8% killing) and, when stimulated with phorbol myristate, produced less superoxide anion (O2-; 0.15 +/- 0.02 O2-/h/mg M phi protein) than M phi from uninfected monkeys (21.8 +/- 1.6% killing and 0.29 +/- 0.02 O2-/h/mg M phi protein). In contrast, killing and O2- release were accentuated in SIV+ asymptomatic animals (25.8 +/- 2.3% killing and 0.40 +/- 0.04 O2-/h/mg M phi protein; p < 0.05). M phi-mediated killing and O2- production could be restored by culturing the affected cells in supernatants derived from Con A-stimulated PBMC of uninfected or SIV+ asymptomatic monkeys. Supernatants with restorative properties had high IFN-gamma bioactivity (63.4 +/- 11.0 U/ml) and elevated IL-10 concentrations (75.3 +/- 10.4 pg/ml) as compared with PBMC supernatants derived from animals with AIDS (IFN-gamma, 9.7 +/- 4.9 U/ml; IL-10, 24.0 +/- 10.1 pg/ml). Functional restoration was found to be dependent, in part, on the presence of IFN-gamma, as neutralizing Abs to IFN-gamma significantly inhibited functional restoration in active supernatants. Moreover, the inactivity of supernatants from mitogen-stimulated PBMC cultures derived from animals with AIDS was not solely dependent upon the loss of CD4+ lymphocytes, inasmuch as purified pulmonary alveolar and peripheral blood CD4+ T cells from only uninfected and SIV+ asymptomatic animals, and not those from animals with AIDS, produced IFN-gamma upon mitogen stimulation. Collectively, these findings suggest that functional aberrations in alveolar M phi from animals with AIDS are not directly due to virus infection but likely result from changes in the pulmonary microenvironment in association with the multisystemic loss and dysfunction of CD4+ T cells.

Macrophage function in simian AIDS. Killing defects in vivo are independent of macrophage infection, associated with alterations in Th phenotype, and reversible with IFN-gamma

Infection of macrophages (M phi) in vitro with M phi-tropic isolates of simian immunodeficiency virus (SIV) did not affect killing of Cryptococcus neoformans up to 16 days after inoculation (p &lt; 0.05). Conversely, alveolar M phi from animals with SIV-induced AIDS killed C. neoformans less efficiently (10.4 +/- 2.8% killing) and, when stimulated with phorbol myristate, produced less superoxide anion (O2-; 0.15 +/- 0.02 O2-/h/mg M phi protein) than M phi from uninfected monkeys (21.8 +/- 1.6% killing and 0.29 +/- 0.02 O2-/h/mg M phi protein). In contrast, killing and O2- release were accentuated in SIV+ asymptomatic animals (25.8 +/- 2.3% killing and 0.40 +/- 0.04 O2-/h/mg M phi protein; p &lt; 0.05). M phi-mediated killing and O2- production could be restored by culturing the affected cells in supernatants derived from Con A-stimulated PBMC of uninfected or SIV+ asymptomatic monkeys. Supernatants with restorative properties had high IFN-gamma bioactivity (63.4 +/- 11.0 U/ml) and elevated IL-10 concentrations (75.3 +/- 10.4 pg/ml) as compared with PBMC supernatants derived from animals with AIDS (IFN-gamma, 9.7 +/- 4.9 U/ml; IL-10, 24.0 +/- 10.1 pg/ml). Functional restoration was found to be dependent, in part, on the presence of IFN-gamma, as neutralizing Abs to IFN-gamma significantly inhibited functional restoration in active supernatants. Moreover, the inactivity of supernatants from mitogen-stimulated PBMC cultures derived from animals with AIDS was not solely dependent upon the loss of CD4+ lymphocytes, inasmuch as purified pulmonary alveolar and peripheral blood CD4+ T cells from only uninfected and SIV+ asymptomatic animals, and not those from animals with AIDS, produced IFN-gamma upon mitogen stimulation. Collectively, these findings suggest that functional aberrations in alveolar M phi from animals with AIDS are not directly due to virus infection but likely result from changes in the pulmonary microenvironment in association with the multisystemic loss and dysfunction of CD4+ T cells.

Recruitment of lymphocytes during cutaneous delayed hypersensitivity in nonhuman primates is dependent on E-selectin and vascular cell adhesion molecule 1

Previous investigations of cutaneous delayed hypersensitivity (DHR) in humans and animals have demonstrated that lymphocyte recruitment from blood is temporally and spatially associated with the de novo, asynchronous expression of both vascular cell adhesion molecule 1 (VCAM-1) and E-selectin on dermal endothelium. In this study, DHR was induced in rhesus monkeys sensitized against tuberculin in order to investigate the contribution of E-selectin and VCAM-1 in lymphocyte recruitment to skin. Intravenous infusions of neutralizing doses of F(ab')2 fragments of murine antibodies to either E-selectin or VCAM-1 during the early inductive phases of DHR showed that murine IgG localized to dermal endothelium at the site of DHR in a pattern kinetically similar to the expression of each endothelial adhesion protein. Most importantly, the relative numbers of lymphocytes localized to the inflammatory site were significantly reduced in DHR modified with infusions of antibodies to either VCAM-1 or E-selectin, while the numbers of lymphocytes recruited to skin in the animal given F(ab')2 fragments of an irrelevant murine monoclonal antibody of the same isotype and at the same dose were not changed. Moreover, in individual animals, the relative inhibition achieved with a particular antibody was proportional to the magnitude of expression of the targeted adhesion protein. Therefore, both VCAM-1 and E-selectin are functionally relevant in the genesis of cutaneous DHR, and each appears to contribute to lymphocyte recruitment in relation to its relative degree of expression in any one particular animal.

Kinetic expression of endothelial adhesion molecules and relationship to leukocyte recruitment in two cutaneous models of inflammation

BACKGROUND

Adhesive interactions between circulating leukocytes and endothelium is requisite for subsequent leukocyte extravasation at inflammatory sites. These adhesive events are mediated by a repertoire of proteins and carbohydrate moieties on both leukocyte and endothelial membranes. Understanding the kinetic expression of these adhesion molecules during an inflammatory cascade in vivo is important for the design and testing of rational therapeutic approaches directed at the blockade of adhesion molecule function in inflammatory disease.

EXPERIMENTAL DESIGN

Two cutaneous inflammatory models were examined using healthy rhesus monkeys. Acute cutaneous injury was studied during a 72-hour period by intradermal injection of endotoxin (lipopolysaccharide) and subsequent biopsy. These tissues were then compared with those obtained from a cutaneous delayed-type hypersensitivity reaction (DHR), elicited by intradermal injections of mammalian tuberculin in sensitized animals and followed for up to 11 days. Expression of E-selectin, P-selectin, VCAM-1, and ICAM-1 was assessed using immunohistochemistry and compared with leukocyte localization and immunohistochemical expression of interleukin (IL) 1, IL-8 and tumor necrosis factor-alpha (TNF-alpha). Finally, relevant adhesion ligands on leukocytes were assessed using flow cytometry.

RESULTS

The lipopolysaccharide model was characterized by early (0.5 hours) and sustained (up to 72 hours) expression of E-selectin on the superficial dermal vasculature, with maximal expression by 8 hours. The expression of VCAM-1 was either not detected or minimal. Neutrophil localization, as detected by elastase immunoreactivity, paralleled E-selectin expression with a 4- to 12-hour lag phase, being maximal by 24 hours. In contrast, DHR was characterized by the dual asynchronous expression of both E-selectin and VCAM-1. Localization of CD2+ lymphocytes, representing the predominant cell type recruited, kinetically followed the expression of E-selectin and VCAM-1, being maximal in number at approximately 48 hours after peak expression of both of these endothelial proteins. Neutrophil recruitment in lipopolysaccharide-induced injury was associated with immunohistochemical localization of TNF-alpha, IL-1, and IL-8, whereas only TNF-alpha was consistently detected in DHR. During DHR, blood lymphocyte expression of L-selectin, VLA-4 (CD49d; alpha chain), and lymphocyte function-associated antigen 1 (both CD11a (alpha chain) and CD18 (beta chain)) did not change.

CONCLUSIONS

The results from this study demonstrate that cutaneous inflammatory infiltrates of varying cellular compositions are associated temporally and spatially with unique patterns of endothelial adhesion molecule and cytokine expression.

Monocyte adhesion to endothelium in simian immunodeficiency virus-induced AIDS encephalitis is mediated by vascular cell adhesion molecule-1/alpha 4 beta 1 integrin interactions

Because the mechanisms associated with recruitment of monocytes to brain in AIDS encephalitis are unknown, we used tissues from rhesus monkeys infected with simian immunodeficiency virus (SIV) to examine the relative contributions of various adhesion pathways in mediating monocyte adhesion to endothelium from encephalitic brain. Using a modified Stamper and Woodruff tissue adhesion assay, we found that the human monocytic cell lines, THP-1 and U937, and the B cell line, Ramos, preferentially bound to brain vessels from monkeys with AIDS encephalitis. Using a combined tissue adhesion/immunohistochemistry approach, these cells only bound to vessels expressing vascular cell adhesion molecule-1 (VCAM-1). Furthermore, pretreatment of tissues with antibodies to VCAM-1 or cell lines with antibodies to VLA-4 (CD49d) inhibited adhesion by more than 70%. Intercellular adhesion molecule-1 (ICAM-1)/beta 2 integrin interactions were not significant in mediating cell adhesion to the vasculature in encephalitic simian brain using a cell line (JY) capable of binding rhesus monkey ICAM-1. In addition, selectin-mediated interactions did not significantly contribute to cell binding to encephalitic brain as there was no immunohistochemical expression of E-selectin and P-selectin in either normal or encephalitic brain, nor was there a demonstrable adhesive effect from L-selectin using L-selectin-transfected 300.19 cells on simian encephalitic brain. These results demonstrate that using the tissue adhesion assay, THP-1, U937, and Ramos cells bind to vessels in brain from animals with AIDS encephalitis using VCAM-1/alpha 4 beta 1 integrin interactions and suggest that VCAM-1 and VLA-4 may be integral for monocyte recruitment to the central nervous system during the development of AIDS encephalitis.

Disseminated B virus infection in a cynomolgus monkey

A cynomolgus monkey (Macaca fascicularis) was euthanatized 1 week following dystocia because of severe peritonitis. Histologic examination revealed lesions characteristic of herpesvirus infection in lungs, liver, spleen, bone marrow, uterus, and adrenal gland, and on the serosal surface of intestines, pancreas, and reproductive tract. Immunohistochemical studies on liver and lungs revealed Herpes B-like antigens in the lesions. B virus was isolated from serum. As systemic B-virus infection was not diagnosed before death of the monkey, these findings underscore the need for universal precautions when handling blood, fluids, or tissues from macaques.

Analysis of simian immunodeficiency virus sequence variation in tissues of rhesus macaques with simian AIDS

One rhesus macaque displayed severe encephalomyelitis and another displayed severe enterocolitis following infection with molecularly cloned simian immunodeficiency virus (SIV) strain SIVmac239. Little or no free anti-SIV antibody developed in these two macaques, and they died relatively quickly (4 to 6 months) after infection. Manifestation of the tissue-specific disease in these macaques was associated with the emergence of variants with high replicative capacity for macrophages and primary infection of tissue macrophages. The nature of sequence variation in the central region (vif, vpr, and vpx), the env gene, and the nef long terminal repeat (LTR) region in brain, colon, and other tissues was examined to see whether specific genetic changes were associated with SIV replication in brain or gut. Sequence analysis revealed strong conservation of the intergenic central region, nef, and the LTR. However, analysis of env sequences in these two macaques and one other revealed significant, interesting patterns of sequence variation. (i) Changes in env that were found previously to contribute to the replicative ability of SIVmac for macrophages in culture were present in the tissues of these animals. (ii) The greatest variability was located in the regions between V1 and V2 and from "V3" through C3 in gp120, which are different in location from the variable regions observed previously in animals with strong antibody responses and long-term persistent infection. (iii) The predominant sequence change of D-->N at position 385 in C3 is most surprising, since this change in both SIV and human immunodeficiency virus type 1 has been associated with dramatically diminished affinity for CD4 and replication in vitro. (iv) The nature of sequence changes at some positions (146, 178, 345, 385, and "V3") suggests that viral replication in brain and gut may be facilitated by specific sequence changes in env in addition to those that impart a general ability to replicate well in macrophages. These results demonstrate that complex selective pressures, including immune responses and varying cell and tissue specificity, can influence the nature of sequence changes in env.

Restricted replication of simian immunodeficiency virus strain 239 in macrophages is determined by env but is not due to restricted entry

Virus derived from the infectious, pathogenic, molecular clone of simian immunodeficiency virus (SIV) called SIVmac239 replicates poorly in primary rhesus monkey alveolar macrophage cultures. Variants with three to nine amino acid changes in the envelope replicate 100 to 1,000 times more efficiently in these macrophage cultures than parental SIVmac239. Early events, including virus entry into cells, were analyzed by measuring the amounts of newly synthesized viral DNA 14 to 16 h after infection of macrophages by using a quantitative polymerase chain reaction method. SIVmac239 ws found to enter macrophages with an efficiency similar to that of the macrophage-tropic derivatives. The assay indeed measured newly synthesized viral DNA since detection was inhibited by the reverse transcriptase inhibitors azidothymidine and foscarnet and by heat inactivation of the virus stock prior to infection. Furthermore, entry of SIVmac239 and macrophage-tropic variant into macrophages was inhibited by monoclonal antibody against CD4. Analysis of the time course of viral DNA accumulation showed that although initial entry of SIVmac239 into cells occurred normally, subsequent logarithmic increases in the amounts of viral DNA associated with spread of virus through the macrophage cultures was blocked. Increasing the amount of SIVmac239 incubated with macrophages increased the amount of virus entering the cell, but this could not overcome the block to replication. Thus, restricted replication of SIVmac239 in macrophages is determined by the envelope, but surprisingly it is not due to restricted virus entry.

An immunohistologic study of granulomatous inflammation in SIV-infected rhesus monkeys

We studied granulomatous inflammation in simian AIDS using histologic, immunohistologic, and in situ hybridization techniques. Complete Freund's adjuvant was used to induce granulomas in two control animals and two macaques infected with simian immunodeficiency virus (SIV) and having low peripheral CD4+ T cell counts. Control animals developed large (> 2 cm diameter) epithelioid granulomas containing CD68+ macrophages (m phi s), epithelioid m phi s and multinucleated giant cells (MNGCs), CD4+ and CD8+ T cells, and small perivascular collections of CD20+ B cells. Lymphocytes rarely expressed proliferating cell nuclear antigen (Ki-67), and only rare endothelial cells expressed vascular cell adhesion molecule 1 (VCAM-1). In contrast, SIV+ animals had smaller (< 0.5 cm diameter) epithelioid granulomas characterized by numerous large, dense CD8+, CD20+ lymphocyte aggregates with prominent local division (Ki-67+). Despite low blood CD4+ T cell numbers, there was a substantial CD4+ T cell infiltrate, accompanied by enhanced endothelial VCAM-1 expression. These granulomas contained no detectable SIV antigen or RNA. Thus, in simian AIDS, experimentally induced granulomatous responses are grossly attenuated, yet associated with increased local endothelial-leukocyte signaling and lymphocyte division.

Clinical and pathologic findings in infant rhesus macaques infected with SIVsmm by maternal transmission

Three of 12 infant rhesus macaques became infected at 9 to 12 months of age with SIVsmm through maternal-infant transmission. Clinical problems seen in one or more infants included decreased CD4 cells, hypergammaglobulinemia, diarrhea, weight loss, anemia, bacterial infections, and terminal respiratory and CNS problems. Gross and histologic lesions due to both primary SIV infection and opportunistic infections were observed. The SIV-infected infants had clinical, immunologic, and pathologic similarities to those seen in pediatric HIV infection.

Elevated vascular cell adhesion molecule-1 in AIDS encephalitis induced by simian immunodeficiency virus

AIDS encephalitis is a common sequela to HIV-1 infection in humans and simian immunodeficiency virus (SIVmac) infection in macaques. Although lentiviral-infected macrophages comprise parenchymal inflammatory infiltrates in affected brain tissue, the mechanisms responsible for leukocyte trafficking to the central nervous system in AIDS are unknown. In this study, we investigated the expression of various endothelial-derived leukocyte adhesion proteins in SIVmac-induced AIDS encephalitis. Encephalitic brains from SIVmac-infected macaques, but not uninflamed brains from other SIVmac-infected animals, were found to express abundant vascular cell adhesion molecule-1 (VCAM-1) protein on the majority of arteriolar, venular, and capillary endothelial cells. Soluble VCAM-1 concentrations in cerebrospinal fluid (CSF) from encephalitic animals were increased approximately 20-fold above those from animals without AIDS encephalitis. Expression of other endothelial-related adhesion molecules, including E-selectin, P-selectin, and intercellular adhesion molecule-1 (ICAM-1), was not uniformly associated with AIDS encephalitis. Thus, the presence of VCAM-1 in both brain and CSF was uniformly associated with SIVmac-induced disease of the central nervous system, and this expression may, at least in part, influence monocyte and lymphocyte recruitment to the central nervous system during the development of AIDS encephalitis. Moreover, measurement of soluble VCAM-1 in CSF may assist in the clinical assessment of animals or people with AIDS.

Arteriopathy in macaques infected with simian immunodeficiency virus

BACKGROUND

An arteriopathy characterized by intimal and medial thickening and fibrosis was seen in 19 of 85 rhesus monkeys infected with simian immunodeficiency virus (SIV), a lentivirus with morphologic, genetic, and biologic similarities to HIV-1 and HIV-2.

EXPERIMENTAL DESIGN

All cases of simian AIDS in rhesus monkeys at the New England Regional Primate Research Center, resulting from either experimental or naturally acquired SIV infection, were retrospectively examined for evidence of histopathologic changes to the vasculature. Of the 85 SIV-related deaths recorded in the pathology files to date, tissues from 19 animals were chosen for further study because of thickening, disruption, inflammation, or other abnormality to any layer of the vascular wall. The lesion was characterized by special stains, immunoperoxidase procedures, and ultrastructural examination.

RESULTS

Affected monkeys of both sexes varied in age from 4 months to 17 years at the time of inoculation and survived from 41 days to 4 years after infection. Pulmonary arteries were affected in all 19 animals, while vessels in other parenchymal organs were involved less frequently. In addition to sometimes marked intimal thickening with luminal occlusion, the internal elastic laminae were fragmented and interrupted. Seven of 19 animals had pulmonary thromboses with varying degrees of organization and recanalization. Immunohistochemical studies, special stains, and ultrastructural analyses revealed the thickened intimae to be composed predominantly of collagen, extracellular matrix, and smooth muscle cells. Ultrastructurally, endothelial cells from both early (no intimal thickening) and advanced lesions were plump, vacuolated, and often disorganized and detached from the subendothelial space. Increased numbers of macrophages (CD68+) were found in the adventitia and occasionally in the thickened intima and media. Rare, fully differentiated macrophages (CD68+, 25F9+) were demonstrated in lumina of affected vessels, some of which expressed p27 SIV gag protein. However, the lesion was not uniformly associated with localization of either viral protein or RNA at the site using immunohistochemistry or in situ hybridization, respectively. A similar arterial lesion has been described in children with AIDS.

CONCLUSIONS

The morphologic findings in macaques and their similarity to arteriosclerotic changes induced by experimental endothelial damage in other species collectively suggest that arteriopathy in AIDS may represent a manifestation secondary to primary endothelial injury.

Simian immunodeficiency virus-specific cytotoxic T lymphocytes are present in the AIDS-associated skin rash in rhesus monkeys

An infiltration of CD8+ lymphocytes in the dermis and epidermis underlies the skin rash that commonly occurs as a primary manifestation of an AIDS virus infection. These cutaneous lymphocytes were characterized in simian immunodeficiency virus of macaques (SIVmac)-infected rhesus monkeys. Skin rash-associated lymphocytes exhibited greater lysis of SIVmac-expressing target cells and a higher cloning efficiency for SIVmac-specific effector T cells than PBL. Moreover, both SIVmac envelope- and gag-specific CTL could be readily cloned from these skin rash-associated lymphocytes. In fact, the skin rash-associated CTL exhibited the same MHC restriction and epitope specificity as those CTL derived from PBL. These studies, therefore, demonstrate that the cutaneous infiltrating CD8+ lymphocytes in SIVmac-infected rhesus monkeys include SIVmac-specific CTL. Thus, whereas virus-specific CTL are likely to represent an important mechanism for controlling AIDS virus infections, they also may play a role in the pathogenesis of the skin lesions that occur after this infection.

Simian immunodeficiency virus-specific cytotoxic T lymphocytes are present in the AIDS-associated skin rash in rhesus monkeys

An infiltration of CD8+ lymphocytes in the dermis and epidermis underlies the skin rash that commonly occurs as a primary manifestation of an AIDS virus infection. These cutaneous lymphocytes were characterized in simian immunodeficiency virus of macaques (SIVmac)-infected rhesus monkeys. Skin rash-associated lymphocytes exhibited greater lysis of SIVmac-expressing target cells and a higher cloning efficiency for SIVmac-specific effector T cells than PBL. Moreover, both SIVmac envelope- and gag-specific CTL could be readily cloned from these skin rash-associated lymphocytes. In fact, the skin rash-associated CTL exhibited the same MHC restriction and epitope specificity as those CTL derived from PBL. These studies, therefore, demonstrate that the cutaneous infiltrating CD8+ lymphocytes in SIVmac-infected rhesus monkeys include SIVmac-specific CTL. Thus, whereas virus-specific CTL are likely to represent an important mechanism for controlling AIDS virus infections, they also may play a role in the pathogenesis of the skin lesions that occur after this infection.

Simian virus 40-induced disease in rhesus monkeys with simian acquired immunodeficiency syndrome

Simian virus 40 (SV40) disease was diagnosed in four rhesus monkeys that died with SIV-induced acquired immunodeficiency syndrome (AIDS). One juvenile monkey seroconverted for SV40 6 months after inoculation with SIV and developed severe bilateral tubulointerstitial nephritis. In contrast, progressive multifocal leukoencephalopathy (PML) occurred in two adult monkeys that were seropositive for SV40 before SIV inoculation, as well as a third adult that was naturally infected with SIV and seropositive for SV40 5 years before death. Large intranuclear inclusions containing abundant polyomavirus particles were limited to either renal tubular epithelial cells or oligodendrocytes. In situ DNA hybridization for SV40 large T antigen further demonstrated that SV40 nucleic acid was localized to either kidney or brain tissue. By immunohistochemical analysis, areas of central nervous system inflammation and demyelination were shown to contain CD68+ macrophages (gitter cells), aggregates of CD8+ T lymphocytes, and numerous gemistocytic astrocytes that labeled for glial fibrillary acidic protein. These observations indicate that rhesus monkeys with SIV-induced AIDS are predisposed to polyomaviral disease, in which SV40 nucleic acid is observed in renal tissue in primary infections and brain tissue after viral reactivation. Furthermore, this organ-specific replication suggests that tissue-tropic strains of SV40 may develop in immunodeficient monkeys.

Complex determinants of macrophage tropism in env of simian immunodeficiency virus

Macrophage-tropic virus variants evolved during the course of infection of individual rhesus monkeys with cloned, non-macrophagetropic simian immunodeficiency virus. Specific changes in the envelope gene (env) were found to be primarily responsible for the dramatic increase in the ability of the virus to replicate in macrophages. Cloned viruses differing at nine amino acid positions in env exhibited a more than 100-fold difference in replicative capacity for primary cultures of rhesus monkey alveolar macrophages. At least five of the nine amino acid changes contributed to macrophage tropism. These determinants were distributed across the full length of env, including both the gp120 and gp41 products of the env gene. Furthermore, the emergence of macrophagetropic variants in vivo was associated with specific pathologic manifestations in which the macrophage is the major infected cell type. Thus, major determinants of macrophage tropism reside in env, they can be complex in nature, and the presence of macrophage-tropic virus variants in vivo can influence the disease course and disease manifestations.

Pathologic features of SIV-induced disease and the association of macrophage infection with disease evolution

Since the original isolation of simian immunodeficiency virus (SIV) from a macaque with an AIDS-like disease, numerous studies have demonstrated the close biologic and genetic relationship of the SIVs to the HIVs. Probably most important, the clinical spectrum of disease associated with SIVmac/SIVsmm infection in rhesus monkeys is strikingly similar to AIDS in HIV-1-infected human beings. Herein are summarized the pathologic features of SIVmac-induced disease in a cohort of rhesus monkeys, with special reference to the role of infected macrophages in the development of AIDS-related manifestations.

Cytokine influence on simian immunodeficiency virus replication within primary macrophages. TNF-alpha, but not GMCSF, enhances viral replication on a per-cell basis

The control of HIV-1 or SIV replication within macrophages is probably influenced by a variety of viral and cellular factors. Of the cellular factors, the authors have studied cytokine influence on SIV replication in vitro utilizing simian alveolar macrophages and uncloned SIVmacMTV, a macrophage-tropic variant. The approach allowed quantification of viral replication on a per-cell basis. As reported for HIV-1 replication in macrophages, TNF-alpha significantly increased SIV production in these macrophage cultures. GMCSF also resulted in marked increases in SIV gag protein in culture supernatants. However, after correcting for differences in total cell numbers and numbers of gag-containing cells in the treated and untreated cultures, GMCSF did not upregulate SIV production on a per-cell basis. IL-6 increased SIV replication little if at all but induced significantly greater cytopathic changes in the treated cultures compared with infected, untreated cultures. In contrast, IFN-gamma greatly decreased replication. Our results for GMCSF, IFN-gamma, and IL-6 are in contrast to previously published reports of cytokine control of HIV-1 growth in target cells, and they stress the importance of cell number analyses and the use of primary cultures in the study of lentiviral replication kinetics in macrophages.

Effect of simian immunodeficiency virus infection on tumor necrosis factor-alpha production by alveolar macrophages

We studied the release of tumor necrosis factor-alpha (TNF alpha), a vital immunoregulatory cytokine, by alveolar macrophages (M phi s) infected with simian immunodeficiency virus (SIV) in vitro or collected from SIV-infected macaques. For in vitro studies, M phi s were harvested by bronchoalveolar lavage from 5 normal animals and infected in flasks with SIV (10(4)TCID50/2.5 x 10(6) M phi s). After 7 to 10 days, cytopathic effect was prominent and 68 +/- 2% of M phi s were immunoreactive for p27 core protein. Uninfected (control) and SIV-infected M phi s were then cultured for 24 hours in 96-well plates (10(5) M phi s/well) while challenged with lipopolysaccharide (LPS; 100 micrograms/ml). TNF alpha was assayed in culture supernatants by an enzyme-linked immunosorbent assay (detection limit, 50 pg/ml) and results were expressed as pg TNF alpha/ml/10(3) M phi s (mean +/- SEM). TNF alpha was not detected in unstimulated wells. TNF alpha release by control and SIV-infected M phi s was similar (6.6 +/- 0.7 and 7.9 +/- 1.1 pg/ml/10(3) M phi s, respectively). We also studied TNF alpha release by alveolar M phi s from 8 animals infected with SIV (3 asymptomatic, 5 with acquired immune deficiency syndrome virus (AIDS]. One animal with AIDS had p27+ M phi s. Alveolar M phi s from asymptomatic animals released significantly more TNF alpha (10.3 +/- 1.1 pg/ml/10(3) M phi s) than did animals with AIDS or uninfected macaques (5.2 +/- 0.8 and 7.0 +/- 0.6 pg/ml/10(3) M phi s, respectively) (p less than 0.01). However, M phi s from monkeys with AIDS failed to respond to LPS after 7 to 10 days in culture. In summary, in vitro infection with SIV does not cause constitutive TNF alpha release or alter the response of cultured M phi s to LPS. When kept in culture, M phi s collected from asymptomatic, SIV-infected animals retain their response to LPS, whereas M phi s from animals with AIDS lose the capacity to produce TNF alpha. Furthermore, M phi s cytokine production is exaggerated before overt clinical disease, but not as a direct result of infection with SIV.

Macrophage-tropic variants of SIV are associated with specific AIDS-related lesions but are not essential for the development of AIDS

The importance of macrophage infection for the development of acquired immune deficiency syndrome (AIDS) was investigated. Molecularly cloned simian immunodeficiency virus (SIV)mac239 replicates very poorly in cultured macrophages yet it causes AIDS in rhesus monkeys. Three of five rhesus monkeys that died with AIDS following SIVmac239 infection showed no disease manifestations directly associated with macrophage infection, such as encephalitis and granulomatous interstitial pneumonia. Simian immunodeficiency virus recovered from the peripheral blood of these three animals at or near the time of death replicated very poorly if at all in cultured macrophages, and tissues taken at autopsy showed little or no infection of macrophages by immunohistochemical staining. However two of the five rhesus monkeys that died with AIDS following SIVmac239 infection displayed a characteristic SIV-related meningoencephalitis and/or granulomatous pneumonia, lesions associated with macrophage infection. Simian immunodeficiency virus recovered from the peripheral blood of these two animals near the time of death replicated extremely well in cultured macrophages, indicating the emergency of macrophage-tropic variants in vivo. Furthermore tissues taken at autopsy from these two showed many infected macrophages by immunohistochemical staining. These results indicate that AIDS and death can occur without obvious involvement of macrophage infection. However the presence of macrophage-tropic viral strains appears to influence the disease course and disease manifestations.

A chimpanzee-passaged human immunodeficiency virus isolate is cytopathic for chimpanzee cells but does not induce disease

The human immunodeficiency virus type 1 (HIV-1) readily infects both humans and chimpanzees, but the pathologic outcomes of infection in these two species differ greatly. In attempts to identify virus-cell interactions that might account for this differential pathogenicity, chimpanzee peripheral blood lymphocytes and bone marrow macrophages were assessed in vitro for their ability to support the replication of several HIV-1 isolates. Although the IIIb, RF, and MN isolates did not readily infect chimpanzee peripheral blood lymphocytes, an isolate of HIV-1 passaged in vivo in chimpanzees not only replicated well in both chimpanzee peripheral blood lymphocytes and bone marrow macrophages but also was cytopathic for chimpanzee CD4+ lymphocytes. Because no evidence of HIV-induced disease has been observed in chimpanzees infected with this isolate, in vitro replication to high titers with concomitant loss of CD4+ cells is not, in this instance, a correlate of pathogenicity. These observations, therefore, indicate that caution must be used when making extrapolations from in vitro data to in vivo pathogenesis.

Importance of the nef gene for maintenance of high virus loads and for development of AIDS

When rhesus monkeys were infected with a form of cloned SIVmac239 having a premature stop signal at the 93rd codon of nef, revertants with a coding codon at this position quickly and universally came to predominate in the infected animals. This suggests that there are strong selective forces for open functional forms of nef in vivo. Although deletion of nef sequences had no detectable effect on virus replication in cultured cells, deletion of nef sequences dramatically altered the properties of virus in infected rhesus monkeys. Our results indicate that nef is required for maintaining high virus loads during the course of persistent infection in vivo and for full pathologic potential. Thus, nef should become a target for antiviral drug development. Furthermore, the properties of virus with a deletion in nef suggest a means for making live-attenuated strains of virus for experimental vaccine testing.

Study of long-term cultures of simian immunodeficiency virus (SIVmac 251)-infected peripheral blood lymphocytes

A culture of rhesus monkey peripheral blood lymphocytes was divided into two parts; one was kept as an uninfected control, and the other was infected with a strain of simian immunodeficiency virus (SIVmac251) originally isolated from a rhesus monkey that died of a malignant lymphoma associated with acquired immune deficiency syndrome. Both cultures were sampled at successive intervals from 1 to 40 days postinfection. Each sample was subjected to in situ hybridization for detection of viral mRNA, immunocytochemical detection of viral core protein (p27), reverse transcriptase assay, electron microscopy, and immunophenotypic characterization of infected cells. These techniques were used to define viral growth kinetics of this novel lentivirus in peripheral blood lymphocytes. The first evidence of SIVmac251 replication was obtained by an in situ hybridization signal for viral mRNA at 2 days postinoculation. This was followed by detection of viral p27 core protein by immunocytochemistry on day 4. Reverse transcriptase activity above control values was not detected until day 8. Budding particles were not found in the infected cultures until 14 days postinfection. Results of in situ hybridization, immunocytochemistry, and reverse transcriptase assay indicated that two bursts of viral replication occurred during the course of this study. The first, at 3 weeks postinfection, was due to infection and subsequent depletion of CD4+ lymphocytes, while the second, 3 weeks later, resulted from a cycle of replication in CD8+ lymphocytes and the remaining CD4+ cells, culminating in the death of all cells on day 39 postinoculation.

Soluble and membrane-associated interleukin 2 receptor-alpha expression in rhesus monkeys infected with simian immunodeficiency virus

More than 80% of rhesus monkeys infected with simian immunodeficiency virus (SIV) were found to have elevated levels of soluble interleukin-2 receptor (IL-2R) in their serum during the course of infection. All long-term survivors had stably elevated levels of soluble IL-2R. The highest levels of soluble IL-2R correlated with the expression of IL-2R on tissue macrophages. Although IL-2R expression was induced on alveolar macrophages by infection with SIV in vitro, expression of IL-2R on tissue macrophages in vivo was not associated with concurrent SIV protein expression in the same cells. Moreover, in animals with high soluble IL-2R levels, there was an inverse relationship between the numbers of cells expressing IL-2R and cells expressing viral protein. The results suggest that the induction of IL-2R may be an indirect or secondary effect of SIV infection. Changes in expression of macrophage-elaborated factors, such as that of IL-2R described in this report, may play a crucial role in some of the pathologic features of acquired immunodeficiency syndrome.

Simian immunodeficiency virus inhibits bone marrow hematopoietic progenitor cell growth

The pathogenic mechanisms underlying the depressed hematopoietic functions seen in human immunodeficiency virus-infected individuals were explored in rhesus monkeys infected with the simian immunodeficiency virus of macaques (SIVmac). Bone marrow hematopoietic progenitor cell colony formation, both granulocyte/macrophage (CFU-GM) and erythrocyte (BFU-E), was shown to be decreased in number in SIVmac-infected rhesus monkeys. SIVmac was readily isolated from bone marrow cells of infected monkeys and was shown to be harbored in macrophages rather than T lymphocytes. The in vitro infection of normal bone marrow cells by SIVmac inhibited colony formation. A striking in vivo correlation between increased SIVmac load in bone marrow cells and decreased hematopoietic progenitor cell colony growth was also shown. Finally, inhibition of SIVmac replication in bone marrow macrophages resulted in increased progenitor cell colony growth from bone marrow cells. These results suggest that the infection of bone marrow macrophages by the acquired immunodeficiency syndrome (AIDS) virus may contribute to depressed bone marrow hematopoietic progenitor cell growth. Moreover, inhibition of AIDS virus replication in these macrophages might induce significant improvement in hematopoietic function.

Vaccine protection against simian immunodeficiency virus infection

Rhesus monkeys were immunized by multiple inoculations with purified, disrupted, noninfectious simian immunodeficiency virus (SIV) in adjuvant. Immunized monkeys developed anti-SIV antibodies detectable by whole-virus ELISA and by immunoblot reactivity; these antibodies had weak neutralizing activity. One week after the last immunization, monkeys were challenged with 200-1000 animal infectious doses of uncloned, live SIV. The same strain of SIV that was used for vaccination was also used for challenge. Anamnestic antibody responses and SIV recovery from peripheral blood were used to evaluate infection following the live virus challenge; two of six vaccinated monkeys showed no evidence of infection following the live virus challenge. Transfusion of 10 ml of whole blood from these two into uninfected, naive rhesus monkeys did not result infection of the recipients, providing further support for the lack of infection in the two previously vaccinated animals. Four of four unvaccinated control monkeys inoculated with these doses of live SIV became infected and three of these died with AIDS 118-258 days after infection. Only one of the six vaccinated monkeys has died to date. In situ hybridization with lymph node biopsy specimens suggested that the virus load was much higher in control macaques than in vaccinated macaques. These results indicate that vaccination with inactivated whole virus can protect macaques against challenge with live SIV. Furthermore, they provide hope that vaccine protection against human AIDS virus infection may be possible.

CD8+CD4- lymphocyte lines can harbor the AIDS virus in vitro

A detailed definition of AIDS virus-specific T lymphocytes will require the generation and characterization of HIV-1-specific, cloned T cell populations. In our studies, we show that CD8+CD4- lymphocyte lines, derived from PBL of rhesus monkeys infected with simian immunodeficiency virus of macaques and humans infected with HIV-1, can harbor AIDS viruses. CD8+CD4- lymphocyte lines derived from infected individuals are shown to express AIDS virus-encoded proteins and generate reverse transcriptase activity. Infection of these CD8+CD4- lymphocytes is confirmed at the single cell level by the techniques of immunoelectronmicroscopy and two-color immunohistochemistry. This observation suggests that it may prove problematic to generate cloned, functional T lymphocyte populations from AIDS virus-infected individuals and raises the possibility that CD8+CD4- cells may serve as reservoirs for the AIDS viruses.

CD8+CD4- lymphocyte lines can harbor the AIDS virus in vitro

A detailed definition of AIDS virus-specific T lymphocytes will require the generation and characterization of HIV-1-specific, cloned T cell populations. In our studies, we show that CD8+CD4- lymphocyte lines, derived from PBL of rhesus monkeys infected with simian immunodeficiency virus of macaques and humans infected with HIV-1, can harbor AIDS viruses. CD8+CD4- lymphocyte lines derived from infected individuals are shown to express AIDS virus-encoded proteins and generate reverse transcriptase activity. Infection of these CD8+CD4- lymphocytes is confirmed at the single cell level by the techniques of immunoelectronmicroscopy and two-color immunohistochemistry. This observation suggests that it may prove problematic to generate cloned, functional T lymphocyte populations from AIDS virus-infected individuals and raises the possibility that CD8+CD4- cells may serve as reservoirs for the AIDS viruses.

Cellular localization of simian immunodeficiency virus in lymphoid tissues. II. In situ hybridization

Lymph nodes and spleens were collected at autopsy and by biopsy from 29 rhesus monkeys infected with simian immunodeficiency virus (SIV). Lymph nodes were classified morphologically into stages of follicular hyperplasia, follicular involution, follicular depletion with normal or expanded paracortices, follicular and paracortical depletion, granulomatous lymphadenitis, or normal. The distribution of SIV RNA was determined by in situ hybridization using a nick translated, 35S labeled, SIVmac DNA probe. Numbers of SIV-infected cells were rare during follicular hyperplasia, numerous during follicular and paracortical expansion, and rare during follicular and paracortical depletion. The splenic morphology reflected that of the lymph nodes; however, the numbers of SIV-positive cells were uniformly lower. SIV RNA was frequently restricted to a single nucleus within multinucleate syncytial cells in two cases of granulomatous lymphadenitis. These results, combined with those of a previous study, provide evidence for antigen trapping in SIV-infected hyperplastic lymph nodes and for widespread viral infection of macrophages and lymphocytes during paracortical expansion.

Cellular localization of simian immunodeficiency virus in lymphoid tissues. I. Immunohistochemistry and electron microscopy

Simian immunodeficiency virus (SIV) is a lentivirus with genetic relatedness to the human immunodeficiency viruses (HIV-1 and HIV-2). It induces a fatal syndrome in rhesus monkeys that closely parallels the clinical course of AIDS in humans. The authors used double-labeling immunohistochemical procedures on rhesus lymph node and spleen taken during different time periods after SIV infection to localize the p27 gag protein to specific cellular immunophenotypes. In animals with follicular hyperplasia, viral protein was found associated predominantly with follicular dendritic cells. Many of these cells showed ultrastructural alterations consisting of swollen dendritic processes containing electron-dense material. Lentiviral particles were found associated with this cell type only rarely. In lymphoid tissues with other histopathologic changes, macrophages and multinucleate giant cells were the predominant cell types containing detectable quantities of viral protein; smaller numbers of p27+ lymphocytes were present. Ultrastructurally, viral particles were found within the extracellular space adjacent to tissue macrophages and within membrane-bound vacuoles of giant cells and tissue macrophages. These results show that certain histologic patterns seen during the course of infection correlate with the localization of viral antigen to specific cellular immunophenotypes and that during the disease course, viral protein is preferentially localized in sections of lymph node and spleen to cells of the macrophage and dendritic cell lineages.

Use of simian immunodeficiency viruses for AIDS research

Despite frequent statements to the contrary, there are good animal models for AIDS. In this review, we summarize the properties of one of the most useful animal models: infection of rhesus monkeys with simian immunodeficiency virus (SIV). The SIVs are an extensive group of HIV-related lentiviruses of nonhuman primates. They closely resemble the human AIDS viruses, HIV-1 and HIV-2, in both genetic sequence and biological properties. Some SIV isolates, most notably those derived from macaques and mangabeys, induce AIDS in rhesus monkeys in a time frame suitable for laboratory investigation. Rhesus monkeys are not endangered in the wild, they breed well in captivity, and they are available in reasonably large numbers. Study of SIV has already resulted in seminal contributions regarding the origins of the HIVs, AIDS pathogenesis, and vaccine and therapy research. Continued use of SIV systems will be an important weapon in our arsenal against AIDS.

Immunophenotypic characterization of mononuclear phagocytes and dendritic cells in lymphoid organs of the rhesus monkey

Mononuclear phagocytes and dendritic cells are potent antigen-presenting cells that localize to distinct microenvironmental compartments in many different organs. These cells are particularly plentiful in spleen and lymph node. Recently, these cells have been identified and immunophenotypically characterized in human tissue sections using monoclonal antibodies. However, similar studies in animal species, particularly those representing models of human diseases, have yet to be completely performed. We have evaluated 18 monoclonal reagents raised against human determinants for their reactivity with macrophages and dendritic cells in lymphoid organs of rhesus monkeys. Six of the 18 (EBM11, 25F9, Mol, R4/23, To5, and SK9) produced labeling patterns in rhesus monkey lymphoid tissue that paralleled the staining patterns described for human tissues. Seven others (KB90, FMC17, Mo3, PHM3, PHM2, G16/1, and 27E10) stained varying subsets of specific cells types in these simian tissues. These reagents are requisite for the future study in an experimental animal of the afferent immune response in both normal and disease states.

Prevalence of antibodies to 3 retroviruses in a captive colony of macaque monkeys

The prevalence of antibodies to 3 retroviruses in the macaque colony of the New England Regional Primate Research Center (NERPRC) was determined using enzyme-linked immunosorbent assay procedures as well as radioimmunoprecipitation-SDS polyacrylamide gel electrophoresis and indirect immunofluorescence tests. Out of 848 macaques, 3 (0.35%) had antibodies to simian immunodeficiency virus (SIV), 27 (3.2%) had antibodies to simian T-lymphotropic virus type I (STLV-1) and approximately 285 (34%) had antibodies to type D retrovirus. Of 3 macaques infected with SIV, 2 were rhesus monkeys (Macaca mulatta) and I was a cynomolgus monkey (Macaca fascicularis). STLV-1 and D retrovirus infection occurred in all 4 macaque species examined. SIV, STLV-1 and D retroviruses were isolated from sero-positive macaques. The low prevalence of SIV infection suggests that SIV is not being readily transmitted among macaques at NERPRC; this contrasts markedly with the high SIV prevalence in some captive mangabey colonies. In contrast to African green monkeys from eastern Africa, 160 Caribbean green monkeys examined showed no sign of SIV infection. These results provide a framework for monitoring spontaneous disease associated with infection by these 3 retroviruses and will help in further definition of STLV-1 and SIV infection of non-human primates as animal models for human disease.