Enhanced accessory cell function by alveolar macrophages from patients infected with the human immunodeficiency virus: potential role for depletion of CD4+ cells in the lung

Abnormalities in host defense associated with HIV infection

The broad variety of pulmonary infections encountered in human immunodeficiency virus (HIV)-infected individuals demonstrates that the host defense network is impaired. An improved understanding of these events in the lung can lead to specific interventions aimed at restoration of deficient function. This review summarizes the pulmonary host defense deficits in HIV-infected individuals, focusing on lymphocytes, alveolar macrophages, and neutrophils.

HIV-Related Lung Disorders

Highly active antiretroviral therapy (HAART) has dramatically altered the spectrum of morbidity and mortality in HIV-infected patients. This has been attributed to improvements in the lung microenvironment leading to enhanced pulmonary immunity, either by preventing the progressive loss of immune function or by actually promoting immune restoration. However, these changes have been accompanied by the recognition of new pulmonary complications in HIV-infected subjects, especially those associated with immune reconstitution. In this review we will describe how HIV infection alters the normal pulmonary environment, highlight the effect of HAART on these perturbations, and discuss potential complications of HAART in the lung, focusing on the pulmonary immune reconstitution inflammatory syndrome.

The immunocompromised host: HIV infection

The variety of pulmonary infections encountered in HIV-infected individuals indicates that many components of the host defense network are impaired. In addition to depletion of CD4+ T cell numbers, HIV infection results in functional deficits in CD4+ T cells, CD8+ T cells, and natural killer cells. Although some components of macrophage defense are preserved, lack of activation signals from CD4+ T cells contributes to impaired defense by macrophages. There are few data examining the functional capabilities of neutrophils in the lung, but evidence from peripheral blood neutrophils indicates that defense by these cells is also impaired. An improved understanding of these events in the lung during HIV infection could lead to specific interventions aimed at restoration of deficient function.

Human immunodeficiency virus gp120 downregulates CD1d cell surface expression

CD1d is an MHC class I-like surface molecule that presents endogenous glycoplipid antigens. The effect of HIV infection on CD1d surface expression has not yet been reported. FACS analysis revealed significantly lower levels of CD1d on CD14(+) monocytes from HIV-infected subjects compared to HIV-infected subjects on HAART and healthy controls. CD1d expression correlated inversely with viral load in infected individuals. CD1d surface expression on human cell lines was downregulated after infection with M-tropic HIV, T-tropic HIV, or after exposure to HIV gp120 in vitro. These data suggest that CD1d-mediated responses are altered during HIV infection and may thus contribute to the global immunodeficiency seen in these patients.

HIV-1 gp120 chemokine receptor-mediated signaling in human macrophages

The chemokine receptors CCR5 and CXCR4 serve as the cellular receptors in conjunction with CD4 for HIV-1 entry and infection of target cells. Although the virus has subverted these molecules for its own use, their natural function is to respond to activation and migration signals delivered by extracellular chemokines. A principal research objective of our laboratory is to understand the consequences of virus-chemokine receptor interactions for cellular function, as well as for entry and infection. We hypothesized that CXCR4-using (X4) and CCR5-using (R5) HIV-1 strains might elicit signals through the chemokine receptors that result in aberrant function and/or regulate virus entry or postentry steps of infection. We have focused on primary human macrophages, which express both CXCR4 and CCR5, because macrophages are a principal target for HIV-1 in vivo, inappropriate macrophage activation appears to play a major role in the pathogenesis of certain sequelae of AIDS, such as HIV encephalopathy, and macrophage infection is regulated at several steps subsequent to entry in ways that are linked to envelope- receptor interactions. This review summarizes our recent findings regarding the mechanisms of chemokine-receptor signaling in macrophages, the role of viral envelope glycoproteins in eliciting macrophage signals, and how these activation pathways may participate in macrophage infection and affect cell functions apart from infection.

Activation-inactivation of HIV-1 in the lung

The lung is prominently afflicted during the course of HIV-1 disease by both infectious and noninfectious complications. Direct or indirect effects of HIV-1 are likely central to the pathogenesis of these complications. Thus, any changes in viral load locally would negatively impact on the lung. This review focuses on the endogenous influences (immune effector cells, surfactant) and the exogenous factors (including infections such as tuberculosis and noninfectious exposures like cigarette smoke) that may contribute to activation or inactivation of HIV-1 in the lung.

Hyperthermia enhances cytomegalovirus regulation of HIV-1 and TNF-alpha gene expression

The immediate-early (IE) genes of human cytomegalovirus (CMV) can be expressed in monocytic cells and are known to regulate viral and cellular genes. Reactivation of human immunodeficiency virus (HIV-1) may be stimulated by a variety of factors including other viruses and inflammatory cytokines. These studies examine the role of hyperthermia and CMV in the regulation of HIV-1 and tumor necrosis factor (TNF)-alpha. THP-1 cells were transfected with the CMV IE genes. HIV-1 and TNF-alpha transcription were assessed with chloramphenicol acetyltransferase promoter constructs. Hyperthermia sufficient to stimulate production of heat shock proteins was used to stimulate the cells. Hyperthermia significantly enhances the effect of CMV IE gene products on the expression of HIV-1 and TNF-alpha. The increases in HIV-1 transcription appear to be in part due to increases in TNF-alpha. Heat shock proteins induced by hyperthermia may play an important role in the viral regulation of monocytic function by CMV.

Lymphocytic alveolitis, bronchoalveolar lavage viral load, and outcome in human immunodeficiency virus infection

Lymphocytic alveolitis portends a poor prognosis in human immunodeficiency virus (HIV)-infected subjects. Because alveolar lymphocytes consist predominantly of HIV-specific CD8(+) cytotoxic T lymphocytes (CTL), they could represent an appropriate immune response to infected cells in the lung, and be a surrogate marker for a high pulmonary viral burden. We assessed long-term outcome in a cohort of asymptomatic HIV-infected subjects who underwent bronchoscopy between 1990 and 1993 and had bronchoalveolar lavage fluid (BALF) available for determination of viral load by reverse transcription-polymerase chain reaction. The ability to detect HIV in BALF increased with disease progression. Lymphocytic alveolitis, although present at all stages of HIV infection, was most pronounced in patients with middle stage disease. The HIV viral load as measured by bronchoalveolar lavage correlated with the percentage of alveolar lymphocytes in patients with peripheral blood CD4(+) cell counts above 200/microliter. Including patients with CD4(+) cell counts < 200/microliter weakened this correlation, possibly because of replacement of CD8(+) CTL by CD8(+) suppressor cells in advanced disease. Free virus in BALF was a stronger predictor of HIV disease progression than was lymphocytic alveolitis. These data suggest that lymphocytic alveolitis in HIV-infected subjects occurs in response to viral antigens in the lung and that the poor prognosis associated with lymphocytic alveolitis reflects a high pulmonary viral burden.

Production of interferon-gamma by lung lymphocytes in HIV-infected individuals

A CD8(+) lymphocytic alveolitis occurs in up to 60% of asymptomatic human immunodeficiency virus (HIV)-infected individuals. Early in HIV infection, lymphocytes consist predominantly of cytotoxic T lymphocytes directed against HIV-infected targets. As HIV disease progresses, they are replaced by CD8(+)CD57(+) suppressor cells. Virus-specific cytotoxic T lymphocytes secrete interferon-gamma (IFN-gamma), an important cytokine in upregulating immune responses, primarily through macrophage activation. We examined the ability of lung and blood lymphocytes from HIV-positive patients at various stages of HIV infection to secrete IFN-gamma spontaneously and in response to phytohemagglutinin A. IFN-gamma production and secretion were determined with ELISA, Western blot, immunoprecipitation, and Northern blot techniques. Lung lymphocytes from HIV-infected individuals secreted large amounts of IFN-gamma. However, this ability was lost in patients with late-stage disease. Correlation between blood and lung lymphocyte IFN-gamma secretion was poor, suggesting regional differences in lymphocyte function. These data suggest that lung levels of IFN-gamma are high until late in HIV disease. These findings support the concept of administering exogenous IFN-gamma to patients with late-stage HIV disease and opportunistic infections.

CD80 expression on monocytes in HIV-infected patients

A prominent feature of HIV infection is a progressive anergy of T cells and an increase of activation-dependent T-cell death. CD80 (B7.1), the ligand of CD28, is an important co-stimulatory molecule on antigen-presenting cells that delivers an essential second signal for T-cell activation. To test whether immunologic dysfunction in HIV disease involves CD80, we studied CD80 expression on circulating monocytes in heparinized whole blood of 33 HIV-infected patients and 13 controls. Most monocytes in patients and controls expressed significant amounts of CD80. There was no statistical difference of mean fluorescence intensity (MFI) of CD80 expression when all HIV-infected patients were compared with healthy controls. However, asymptomatic patients in clinical Centers for Disease Control and Prevention (CDC) stage A showed a significantly stronger CD80 expression than did healthy controls. Additionally, patients receiving antiretroviral therapy exhibited significantly higher CD80 expression than did patients not receiving therapy and healthy controls. We did not find a correlation with the presence of HIV p24 antigenemia and counts of CD4+ and CD8+ T cells. Although we studied CD80 expression only on circulating monocytes and not in HIV-infected monocytes or in activated macrophages, our data do not support a role for a general impairment of CD80 expression in induction of anergy in HIV disease.

Functionally relevant changes occur in HIV-infected individuals' alveolar macrophages prior to the onset of respiratory disease

OBJECTIVE

We have compared the phenotypic and functional changes found in alveolar macrophages recovered from the lungs of 39 HIV-positive individuals with no respiratory disease with those from 33 HIV-positive individuals with pneumonitis and 31 healthy controls.

METHODS

Bronchoalveolar lavage (BAL) cell cytospin preparations were stained using monoclonal antibody immunoperoxidase and double immunofluorescence techniques. Cytokine levels within supernatant BAL were determined using enzyme immunoassay.

RESULTS

There were marked differences in alveolar macrophage phenotype between the three groups. In particular, the relative proportion of cells staining RFD1+RFD7- (inducer cells) was reduced in the HIV-positive individuals without respiratory disease. This was correlated with measures of declining systemic immunity. Patients with pneumonitis had the highest levels of measured cytokines [interleukin-1 beta, tumour necrosis factor-alpha and transforming growth factor (TGF)-beta 2], followed by the HIV-positive individuals without respiratory disease. In this latter population a negative correlation was found between active (non acid dissociated) TGF-beta 2 and blood CD4 cell count.

CONCLUSIONS

The differences between the three groups suggest that alterations of potential relevance to the pulmonary immune response are occurring in alveolar macrophages prior to the onset of respiratory disease. This study confirms the importance of investigating asymptomatic HIV-positive individuals.

Immunologic effects of HIV in the lung

This article covers a selected group of topics dealing with the contribution of lung immunocompetent cells in the host defense mechanisms against HIV. These include recent findings suggesting that bidirectional signals between alveolar macrophages and pulmonary cytotoxic T lymphocytes define regulatory networks, which contribute to the accumulation of HIV-specific effector cells in the lung microenvironment. The authors also emphasize the cell pattern of HIV infection in the lung, highlighting the role of the retrovirus in weakening pulmonary host defenses and its spreading into the lower respiratory tract.

Changes to alveolar macrophage phenotype in HIV infected individuals with normal CD4 counts and no respiratory disease

BACKGROUND

It has previously been shown that HIV infected individuals with pneumonitis have identifiable abnormalities in alveolar macrophages obtained by bronchoalveolar lavage (BAL). In particular, alterations in the expression of alveolar macrophage surface antigens associated with macrophage function have been reported. To determine whether these changes reflect HIV infection or the respiratory episode itself, a population of HIV infected patients with no respiratory disease was studied.

METHODS

Twenty two HIV antibody positive individuals with a peripheral blood CD4 count of > 400/microliters and 10 healthy volunteer controls underwent bronchoscopy and BAL. Cytospin preparations from the recovered cells were stained using immunoperoxidase and double immunofluorescence techniques with monoclonal antibodies RFD1, RFD7, EBM11/CD68 (mature macrophages), UCHM1/CD14 (monocyte marker), and HLA-DR (RFDR1). Differential cell counts were also performed.

RESULTS

There was an increase in overall alveolar macrophage HLA-DR expression in the HIV population. This was not reflected in a change in the percentage of cells staining CD14 (monocytes) or CD68 (mature macrophages) positive. The relative proportions of cells staining RFD1 + RFD7- (inducer cells), RFD1 - RFD7+ (effector cells), and RFD1 + RFD7+ (suppressive cells) were unchanged between HIV and control groups.

CONCLUSIONS

In a population of HIV infected individuals with normal CD4 counts and no respiratory disease there was an increase in overall alveolar macrophage HLA-DR expression which occurred independently of any alteration in the relative proportions of alveolar macrophage subpopulations.

Expression of surface markers on alveolar macrophages from symptomatic patients with HIV infection as detected by flow cytometry

Alveolar macrophages (AMs) harvested from 32 HIV-infected patients with respiratory problems (opportunistic pulmonary infections, n = 12; other lung disease, n = 20) and 13 healthy controls were stained with a panel of 15 monoclonal antibodies directed against surface antigens implicated in cell function. Antigen expression was quantified by flow cytometry and expressed as relative linear median fluorescence intensity (RLMFI). On AMs of patients, as compared with controls, there was a significant enhancement of HLA DP (12.1 +/- 1.5 vs 6.5 +/- 0.9, p = 0.01, M +/- SEM, RLMFI units), CD11b (3.4 +/- 0.5 vs 1.7 +/- 0.4, p = 0.014), CD11c (8.9 +/- 1.0 vs 4.8 +/- 0.8, p = 0.0046), CD14 (2.1 +/- 0.3 vs 1.0 +/- 0.2, p = 0.0009), and CD33 (1.7 +/- 0.1 vs 1.0 +/- 0.2, p = 0.0093). No significant differences could be established for HLA-DR (36.9 +/- 5.8 vs 30.9 +/- 7.5, NS), HLA-DQ (3.4 +/- 0.3 vs 3.1 +/- 0.6, NS), CD54 (1.9 +/- 0.3 vs 1.2 +/- 0.1, NS), CD13 (2.5 +/- 0.6 vs 1.5 +/- 0.3, NS), CD36 (1.4 +/- 0.2 vs 0.9 +/- 0.3, NS), CD71 (10.3 +/- 1.9 vs 8.9 +/- 1.8, NS), CD25 (0.8 +/- 0.0 vs 0.9 +/- 0.1, NS), 27E10 (1.1 +/- 0.1 vs 0.8 +/- 0.3, NS), RM3/1 (1.9 +/- 0.4 vs 1.5 +/- 0.4, NS), and CD4 (1.5 +/- 0.3 vs 1.0 +/- 0.0, NS). The expression of CD14 and CD11b, but not of HLA class II antigens and CD71, was increased in the smaller cell population compared with the larger, thus suggesting monocyte recruitment. The increased expression of HLA-DP, CD11c, CD14, and CD33 on the patients' AMs was independent of smoking habits. The degree of immunodeficiency as indicated by the absolute peripheral CD4 count, the character of HIV-related pulmonary disease, and the prophylactic use of pentamidine or zidovudine did not significantly modify the antigen expression pattern. It is concluded that HIV infection may lead, most probably indirectly, to enhanced expression of surface antigens by local upregulation and/or recruitment of monocytes from the peripheral circulation. The functional significance of enhanced marker expression requires further clarification.

Effect of corticosteroids on IL1 beta and TNF alpha release by alveolar macrophages from patients with AIDS and Pneumocystis carinii pneumonia

The mechanisms by which corticosteroids (CCs) improve the outcome of AIDS patients with severe Pneumocystis carinii pneumonia (PCP) are unclear. We studied IL1 beta and TNF alpha release from alveolar macrophages (AMs) of patients receiving CCs for the treatment of PCP and also the effect of in vitro hydrocortisone on this release. Cytokine release from AMs of AIDS patients with pulmonary complications not receiving CCs (group 1) was compared with that from AM of those receiving CCs for PCP (group 2). The AMs of HIV-negative normal subjects (group 3) served as controls. All participants were nonsmokers or exsmokers. We found that lipopolysaccharide-stimulated AM from group 2 released significantly less interleukin-1 beta (IL1 beta) and tumor necrosis factor alpha (TNF alpha) than AM from group 1 and was similar to that from group 3. There was a significant positive correlation between the amount of TNF alpha and IL1 beta released. The presence of HC in the culture medium reduced in vitro IL1 beta and TNF alpha release from stimulated AM of the three groups. Thus, stimulated AMs from AIDS patients who receive CCs for treatment of PCP release significantly less IL1 beta and TNF alpha than AM from patients not receiving CCs. These findings suggest a mechanism by which CCs improve the outcome of AIDS patients with PCP.

Human alveolar macrophages inhibit receptor-mediated increases in intracellular calcium concentration in lymphocytes

Prior studies have demonstrated that human alveolar macrophages (AM) are suppressive of lymphocyte function, through the mechanism of inhibition is unclear. In the current study, human AM inhibited receptor-mediated increases in intracellular calcium concentration ([Ca2+]i) in T cells, natural killer cells, and B cells. This effect was produced by either live or fixed AM, while peripheral blood monocytes caused a minimal reduction in [Ca2+]i. The inhibitory effect of AM was seen following 1 to 2 h of incubation with lymphocytes, was complete at 16 h, and did not affect ionomycin-mediated [Ca2+]i. Inhibition of [Ca2+]i by AM correlated with suppression of T-lymphocyte proliferation and cytotoxic T-lymphocyte activity in response to alloantigen and Staphylococcus A-induced immunoglobulin production. Our findings suggest that a membrane signal on AM is capable of inhibiting receptor-mediated signal transduction in lymphocytes and that this is likely a major mechanism by which immune responses are downregulated in the alveolus.

Pulmonary disease in AIDS patients

Pulmonary disease remains a major complication of the human immunodeficiency virus (HIV). Over the past decade several changes in the pattern of disease have occurred. Pneumocystis carinii pneumonia (PCP) remains the most common opportunistic pathogen in AIDS patients, though its incidence on bronchoscopy has declined and empiric therapy often occurs without a specific diagnosis. Changes in the management of patients with PCP have included different dosages and routes of administration for chemotherapy, improved overall survival, and a recent increase in the number of patients surviving episodes of respiratory failure. In addition, infection with mycobacteria tuberculosis (M.Tb.) has emerged as a major public health problem. The pattern of M.Tb. is distinct from non-immunocompromised patients though response to therapy usually occurs.