Role of alveolar macrophage-T cell adherence in accessory cell function in human immunodeficiency virus-infected individuals

Alveolar macrophages from HIV-infected subjects are resistant to Mycobacterium tuberculosis in vitro

HIV-infected individuals frequently develop Mycobacterium tuberculosis (MTB) infection. Alveolar macrophages (AM) are the initial host defense against this organism. We measured MTB growth in AM from normal and HIV-infected subjects after in vitro exposure. Intracellular growth of MTB was reduced in AM from HIV-infected subjects compared with normal macrophages. This was confined to subjects with CD4 counts greater than 200/microl. Growth of avirulent mycobacteria in HIV macrophages was significantly less than virulent MTB. Because avirulent MTB is more sensitive to tumor necrosis factor-alpha (TNF-alpha), we examined the relationship between cytokine secretion and mycobacterial growth. Higher AM spontaneous TNF-alpha secretion was associated with reduced MTB growth in normal AM. This relationship was not seen in HIV-infected subjects, suggesting that other factors contributed to mycobacteria resistance. Mycobacteria-induced TNF-alpha secretion was inversely associated with growth in normal AM but not in HIV-infected subjects. Finally, binding and internalization of MTB was augmented in HIV macrophages compared with normal, demonstrating that reduced intracellular MTB growth was not due to impaired phagocytosis. In conclusion, the increased incidence of MTB infection in HIV-infected subjects does not appear to be due to a defect in macrophage innate immunity.

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.

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.

HIV and pulmonary immune responses

The lung is a central organ in human immunodeficiency virus (HIV)-induced pathophysiology, becoming infected during the asymptomatic period of the disease. The presence of HIV elicits a discrete virus-specific cytotoxic T lymphocyte (CTL)-mediated immune response in the pulmonary microenvironment. Here, Carlo Agostini and colleagues provide a framework for understanding the mechanisms underlying the spread of the retrovirus and the consequent progression of disease in patients with AIDS-associated lung involvement.