Oxidative responses of human and murine macrophages during phagocytosis of Leishmania chagasi.

Leishmania chagasi, the cause of South American visceral leishmaniasis, must survive antimicrobial responses of host macrophages to establish infection. Macrophage oxidative responses have been shown to diminish in the presence of intracellular leishmania. However, using electron spin resonance we demonstrated that murine and human macrophages produce O2-during phagocytosis of opsonized promastigotes. Addition of the O2- scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl to cultures resulted in increased infection, suggesting that O2- enhances macrophage leishmanicidal activity. The importance of NO. produced by inducible NO synthase (iNOS) in controlling murine leishmaniasis is established, but its role in human macrophages has been debated. We detected NO. in supernatants from murine, but not human, macrophages infected with L. chagasi. Nonetheless, the iNOS inhibitor N(G)-monomethyl-L-arginine inhibited IFN-gamma-mediated intracellular killing by both murine and human macrophages. According to RNase protection assay and immunohistochemistry, iNOS mRNA and protein were expressed at higher levels in bone marrow of patients with visceral leishmaniasis than in controls. The iNOS protein also increased upon infection of human macrophages with L. chagasi promastigotes in vitro in the presence of IFN-gamma. These data suggest that O2- and NO. each contribute to intracellular killing of L. chagasi in human and murine macrophages.

Inducible resistance to oxidant stress in the protozoan Leishmania chagasi.

Leishmania sp. protozoa are introduced into a mammalian skin by a sandfly vector, whereupon they encounter increased temperature and toxic oxidants generated during phagocytosis. We studied the effects of 37 degrees C "heat shock" or sublethal menadione, which generates superoxide and hydrogen peroxide, on Leishmania chagasi virulence. Both heat and menadione caused parasites to become more resistant to H(2)O(2)-mediated toxicity. Peroxide resistance was also induced as promastigotes developed in culture from logarithmic to their virulent stationary phase form. Peroxide resistance was not associated with an increase in reduced thiols (trypanothione and glutathione) or increased activity of ornithine decarboxylase, which is rate-limiting in trypanothione synthesis. Membrane lipophosphoglycan increased in size as parasites developed to stationary phase but not after environmental exposures. Instead, parasites underwent a heat shock response upon exposure to heat or sublethal menadione, detected by increased levels of HSP70. Transfection of promastigotes with L. chagasi HSP70 caused a heat-inducible increase in resistance to peroxide, implying it is involved in antioxidant defense. We conclude that leishmania have redundant mechanisms for resisting toxic oxidants. Some are induced during developmental change and others are induced in response to environmental stress.

Increased in vitro tetanus-induced production of HIV type 1 following in vivo immunization of HIV type 1-infected individuals with tetanus toxoid.

We have previously demonstrated that immunization of HIV-1-infected individuals with the common recall antigen, tetanus, induced transient increases in plasma viremia as well as an increased ability to isolate virus from CD8+ T cell-depleted peripheral blood mononuclear cells (PBMCs) under minimally stimulated culture conditions (IL-2 plus IL-4) postimmunization. In this study, HIV-1-infected individuals were immunized with tetanus toxoid and PBMCs were examined at multiple time points following immunization. Tetanus-induced production of virus was defined as an increased ability to isolate HIV-1 from CD8+ T cell-depleted PBMCs in vitro in the presence of tetanus antigen as opposed to no antigen or control antigen alone. Following immunization, in vitro tetanus-induced production of HIV-1 was observed in 8 of 13 (62%) patients compared to 2 of 13 (15%) patients prior to immunization. In four of these patients, virus could also be isolated from CD8+ T cell-depleted PBMCs in the presence of tetanus without the addition of any exogenous IL-2. Furthermore, virus could be isolated from the unfractionated PBMCs of two patients when tetanus antigen alone was added to the culture in the absence of added PHA or PHA blasts. HIV-1 was isolated predominantly from CD4+ T cells with a CD45RO+, CD25+ phenotype and was associated with a trend to elevated levels in culture supernatants of IFN-gamma, IL-6, TNF-alpha, and IL-4. These findings have important implications with regard to the role of ongoing antigen-specific immune responses in the induction of HIV-1 expression in vivo.

HIV replication in CD4+ T cells of HIV-infected individuals is regulated by a balance between the viral suppressive effects of endogenous beta-chemokines and the viral inductive effects of other endogenous cytokines.

This study demonstrates that the beta-chemokines macrophage inflammatory proteins 1 alpha and 1 beta (MIP-1 alpha and MIP-1 beta) and, RANTES (regulated on activation, normally T-cell expressed and secreted) inhibit human immunodeficiency virus (HIV) replication in anti-CD3 or recall antigen-stimulated peripheral blood mononuclear cells (PBMCs) of asymptomatic HIV-infected subjects. Significant levels of beta-chemokines were produced by both CD4+ and CD8+ PBMC subsets from HIV-infected individuals. Neutralization of endogenous MIP-1 alpha, MIP-1 beta, and RANTES did not rescue HIV replication in cultures to which greater than 10% CD8+ T cells had been added, indicating that the HIV suppressor activity of CD8+ T cells cannot be explained entirely by the beta-chemokines. However, significant enhancement of viral replication was observed upon neutralization of endogenous beta-chemokines in CD8-depleted or CD4+ PBMCs from most donors, particularly in cultures with low inducible levels of HIV production. In contrast, certain endogenous proinflammatory cytokines induced HIV replication in these same cells. These data suggest that the levels of HIV replication in CD4+ PBMC reflect the balance of the opposing effects of endogenous suppressive factors, such as the beta-chemokines, and HIV-inducing cytokines, such as tumor necrosis factor alpha and interleukin 1 beta.

Effect of immunization with a common recall antigen on viral expression in patients infected with human immunodeficiency virus type 1.

BACKGROUND: Activation of the immune system is a normal response to antigenic stimulation, and such activation enhances the replication of human immunodeficiency virus type 1 (HIV-1). We studied the effect of immunization with a common recall antigen on viral expression in HIV-1-infected patients, on the ability to isolate virus, and on the susceptibility to HIV-1 infection of peripheral-blood mononuclear cells (PBMCs) from control subjects not infected with HIV-1. METHODS: Thirteen HIV-1-infected patients and 10 uninfected adults were given a 0.5-ml booster dose of tetanus toxoid. Studies were performed to evaluate changes in the degree of plasma viremia, proviral burden, the ability to isolate HIV-1, and the susceptibility of PBMCs to acute infection in vitro. Two patients underwent sequential lymph-node biopsies for the assessment of viral burden in these tissues. RESULTS: All 13 HIV-1-infected patients had transient increase in plasma viremia after immunization, and the proviral burden increased in 11. These changes did not correlate with the base-line CD4+ T-cell counts. The lymph-node tissue also had increases in the proviral burden and viral RNA after immunization. The virus was more easily isolated from PBMCs from nine of the patients after immunization than before immunization. Despite considerable variability in the results, PBMCs from 7 of the 10 normal subjects were more easily infected in vitro with HIV-1 after immunization than before immunization. CONCLUSIONS: Activation of the immune system by an ongoing antigen-specific immune response to an exogenous stimulus transiently increases the expression of HIV-1 and may enhance the susceptibility of uninfected subjects to HIV-1.

Kinetics of cytokine expression during primary human immunodeficiency virus type 1 infection.

In the present study, we have determined the kinetics of constitutive expression of a panel of cytokines [interleukin (IL) 2, IL-4, IL-6, IL-10, interferon gamma (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha)] in sequential peripheral blood mononuclear cell samples from nine individuals with primary human immunodeficiency virus infection. Expression of IL-2 and IL-4 was barely detected in peripheral blood mononuclear cells. However, substantial levels of IL-2 expression were found in mononuclear cells isolated from lymph node. Expression of IL-6 was detected in only three of nine patients, and IL-6 expression was observed when transition from the acute to the chronic phase had already occurred. Expression of IL-10 and TNF-alpha was consistently observed in all patients tested, and levels of both cytokines were either stable or progressively increased over time. Similar to IL-10 and TNF-alpha, IFN-gamma expression was detected in all patients; however, in five of nine patients, IFN-gamma expression peaked very early during primary infection. The early peak in IFN-gamma expression coincided with oligoclonal expansions of CD8+ T cells in five of six patients, and CD8+ T cells mostly accounted for the expression of this cytokine. These results indicate that high levels of expression of proinflammatory cytokines are associated with primary infection and that the cytokine response during this phase of infection is strongly influenced by oligoclonal expansions of CD8+ T cells.

Role of lymphoid organs in the pathogenesis of human immunodeficiency virus (HIV) infection.

The pathogenic mechanisms of HIV disease are multifactorial and multi-phasic. The common denominator of the disease is the profound immunosuppression that occurs in the vast majority of infected patients. Studies in lymphoid tissues in HIV disease have provided considerable insight into the pathogenic processes involved from the earliest phases of infection through the advanced stages. Following primary infection, virus is disseminated throughout the body and seeds the lymphoid tissue where its replication is only incompletely suppressed and where a reservoir of virus is established. Extracellular virus is trapped within the FDC of the lymph node germinal centers and serves as a source of infection for cells which reside in or migrate through the lymph node throughout the course of infection even during the early and often prolonged asymptomatic period. Eventually, the architecture of the lymphoid tissue is destroyed, compounding the immune dysfunction that results from the depletion of CD4+ T cells. In this regard, the lymphoid tissue of LTNPs is relatively intact and viral burden and replication is considerably lower in the peripheral blood and lymph node mono-nuclear cells of LTNPs than in individuals whose disease progresses. Cytokines probably play a major role in the modulation of HIV expression in the milieu of the lymphoid tissue. Further understanding of the pathogenic mechanisms operative in the lymphoid tissues of HIV-infected individuals will have important implications in the design of therapeutic strategies involving both antiretroviral and immunomodulatory approaches.

Lack of evidence for the dichotomy of TH1 and TH2 predominance in HIV-infected individuals.

A switch from a T helper 1 (TH1) cytokine phenotype to a TH2 phenotype has been proposed as a critical element in the progression of human immunodeficiency virus (HIV) disease. Here, constitutive cytokine expression was analyzed in unfractionated and sorted cell populations isolated from peripheral blood and lymph nodes of HIV-infected individuals at different stages of disease. Expression of interleukin-2 (IL-2) and IL-4 was barely detectable (or undetectable) regardless of the stage of disease. CD8+ cells expressed large amounts of interferon gamma and IL-10, and the levels of these cytokines remained stably high throughout the course of infection. Furthermore, similar patterns of cytokine expression were observed after stimulation in vitro of purified CD4+ T cell populations obtained from HIV-infected individuals at different stages of disease. These results indicate that a switch from the TH1 to the TH2 cytokine phenotype does not occur during the progression of HIV disease.

Effects of three combinations of plyometric and weight training programs on selected physical fitness test items.

To determine the effects of prescribed training programs on 5 physical fitness test items, each of 50 high school boys participated for 10 wk. in one of three programs (wrestling, softball, and plyometrics; weight training; and weight training and plyometrics). (a) On the sit-ups, 40-yd. dash, vertical jump, and pull-ups, each group improved significantly from pre- to posttest. (b) On the shuttle run, none of the groups improved significantly from pre- to posttest. (c) On the vertical jump, groups had a significant effect, but the interaction was nonsignificant. No effects were significant.