Impaired IgG production in the lungs of HIV-infected individuals

Pulmonary Immune Dysregulation and Viral Persistence During HIV Infection

Despite the success of antiretroviral therapy (ART), people living with HIV continue to suffer from high burdens of respiratory infections, lung cancers and chronic lung disease at a higher rate than the general population. The lung mucosa, a previously neglected HIV reservoir site, is of particular importance in this phenomenon. Because ART does not eliminate the virus, residual levels of HIV that remain in deep tissues lead to chronic immune activation and pulmonary inflammatory pathologies. In turn, continuous pulmonary and systemic inflammation cause immune cell exhaustion and pulmonary immune dysregulation, creating a pro-inflammatory environment ideal for HIV reservoir persistence. Moreover, smoking, gut and lung dysbiosis and co-infections further fuel the vicious cycle of residual viral replication which, in turn, contributes to inflammation and immune cell proliferation, further maintaining the HIV reservoir. Herein, we discuss the recent evidence supporting the notion that the lungs serve as an HIV viral reservoir. We will explore how smoking, changes in the microbiome, and common co-infections seen in PLWH contribute to HIV persistence, pulmonary immune dysregulation, and high rates of infectious and non-infectious lung disease among these individuals.

Pathogenesis of HIV-Related Lung Disease: Immunity, Infection, and Inflammation

Despite anti-retroviral therapy (ART), human immunodeficiency virus-1 (HIV)-related pulmonary disease continues to be a major cause of morbidity and mortality for people living with HIV (PLWH). The spectrum of lung diseases has changed from acute opportunistic infections resulting in death to chronic lung diseases for those with access to ART. Chronic immune activation and suppression can result in impairment of innate immunity and progressive loss of T cell and B cell functionality with aberrant cytokine and chemokine responses systemically as well as in the lung. HIV can be detected in the lungs of PLWH and has profound effects on cellular immune functions. In addition, HIV-related lung injury and disease can occur secondary to a number of mechanisms including altered pulmonary and systemic inflammatory pathways, viral persistence in the lung, oxidative stress with additive effects of smoke exposure, microbial translocation, and alterations in the lung and gut microbiome. Although ART has had profound effects on systemic viral suppression in HIV, the impact of ART on lung immunology still needs to be fully elucidated. Understanding of the mechanisms by which HIV-related lung diseases continue to occur is critical to the development of new preventive and therapeutic strategies to improve lung health in PLWH.

The Role of Transforming Growth Factor Beta-1 in the Progression of HIV/AIDS and Development of Non-AIDS-Defining Fibrotic Disorders

Even after attainment of sustained viral suppression following implementation of highly active antiretroviral therapy, HIV-infected persons continue to experience persistent, low-grade, systemic inflammation. Among other mechanisms, this appears to result from ongoing microbial translocation from a damaged gastrointestinal tract. This HIV-related chronic inflammatory response is paralleled by counteracting, but only partially effective, biological anti-inflammatory processes. Paradoxically, however, this anti-inflammatory response not only exacerbates immunosuppression but also predisposes for development of non-AIDS-related, non-communicable disorders. With respect to the pathogenesis of both sustained immunosuppression and the increased frequency of non-AIDS-related disorders, the anti-inflammatory/profibrotic cytokine, transforming growth factor-β1 (TGF-β1), which remains persistently elevated in both untreated and virally suppressed HIV-infected persons, may provide a common link. In this context, the current review is focused on two different, albeit related, harmful activities of TGF-β1 in HIV infection. First, on the spectrum of anti-inflammatory/immunosuppressive activities of TGF-β1 and the involvement of this cytokine, derived predominantly from T regulatory cells, in driving disease progression in HIV-infected persons via both non-fibrotic and profibrotic mechanisms. Second, the possible involvement of sustained elevations in circulating and tissue TGF-β1 in the pathogenesis of non-AIDS-defining cardiovascular, hepatic, pulmonary and renal disorders, together with a brief comment on potential TGF-β1-targeted therapeutic strategies.

Atypical bacterial pneumonia in the HIV-infected population

Human immunodeficiency virus (HIV)-infected individuals are more susceptible to respiratory tract infections by other infectious agents (viruses, bacteria, parasites, and fungi) as their disease progresses to acquired immunodeficiency syndrome. Despite effective antiretroviral therapy, bacterial pneumonia (the most frequently occurring HIV-associated pulmonary illness) remains a common cause of morbidity and mortality in the HIV-infected population. Over the last few decades, studies have looked at the role of atypical bacterial pneumonia (i.e. pneumonia that causes an atypical clinical presentation or responds differently to typical therapeutics) in association with HIV infection. Due to the lack of available diagnostic strategies, the lack of consideration, and the declining immunity of the patient, HIV co-infections with atypical bacteria are currently believed to be underreported. Thus, following an extensive database search, this review aimed to highlight the current knowledge and gaps regarding atypical bacterial pneumonia in HIV. The authors discuss the prevalence of Chlamydophila pneumoniae, Mycoplasma pneumoniae, Coxiella burnetii, Legionella species and others in the HIV-infected population as well as their clinical presentation, methods of detection, and treatment. Further studies looking at the role of these microbes in association with HIV are required. Increased knowledge of these atypical bacteria will lead to a more rapid diagnosis of these infections, resulting in an improved quality of life for the HIV-infected population.

Maternal HIV infection associated with reduced transplacental transfer of measles antibodies and increased susceptibility to disease

BACKGROUND

Transplacental transfer of measles antibodies from mother to fetus is important in protecting against measles during early infancy. Changes in population immunity against measles in adults, including waning of immunity among HIV-infected pregnant women, could affect passive immunity acquired in utero by newborns.

OBJECTIVES

To evaluate the effect of maternal HIV infection on transplacental transfer of measles antibody in mother-newborn dyads in a setting of high maternal HIV prevalence.

STUDY DESIGN

Serum at birth was obtained from 303 mother-newborn dyads, including 196 HIV-infected and 107 HIV-uninfected women, and tested for measles IgG antibodies by ELISA. Seronegativity was defined as antibody levels <150mIU/ml and seroprotective titers as ≥330mIU/ml.

RESULTS

HIV-infected and -uninfected women had similar measles antibody titers, however, cord-blood titers were lower among HIV-exposed (788.06mIU/ml) compared to HIV- unexposed newborns (1306.6mIU/ml; p≤0.001), due to lower transplacental antibody transfer ratio in HIV-exposed (0.63) than in HIV-unexposed newborns (0.97; p≤0.001). Maternal age <25years of age was associated with lower antibody titers and lower percentage with seroprotective titer, as well as less likelihood of their newborns having seroprotective titers (70.2% vs. 86.5%; p=0.001).

CONCLUSIONS

Lower levels of measles antibody in HIV-exposed newborns and in younger women <25years old, increases the susceptibility of their newborns to developing measles. This suggest a need to re-evaluate measles immunization of women of child bearing age and the timing of measles vaccination among infants in settings with a high prevalence of maternal HIV-infection.

Hidden risks for pneumonia in Malawi

Domestic smoke exposure and early HIV infection are critical but unseen risk factors for pneumonia. This paper reviews how recent research in Malawi and elsewhere contributes to an understanding of the possible immunological mechanisms underlying these risks.

Human Immunodeficiency Virus Infection and Host Defense in the Lungs

Immunosuppression associated with human immunodeficiency virus (HIV) infection impacts all components of host defense against pulmonary infection. Cells within the lung have altered immune function and are important reservoirs for HIV infection. The host immune response to infected lung cells further compromises responses to a secondary pathogenic insult. In the upper respiratory tract, mucociliary function is impaired and there are decreased levels of salivary immunoglobulin A. Host defenses in the lower respiratory tract are controlled by alveolar macrophages, lymphocytes, and polymorphonuclear leukocytes. As HIV infection progresses, lung CD4 T cells are reduced in number causing a lack of activation signals from CD4 T cells and impaired defense by macrophages. CD8 T cells, on the other hand, are increased in number and cause lymphocytic alveolitis. Specific antibody responses by B-lymphocytes are decreased and opsonization of microorganisms is impaired. These observed defects in host defense of the respiratory tract explain the susceptibility of HIV-infected persons for oropharyngeal candidiasis, bacterial pneumonia, Pneumocystis pneumonia, and other opportunistic infections.

TGF-β1 epigenetically modifies Thy-1 expression in primary lung fibroblasts

Idiopathic pulmonary fibrosis is a progressive lung disease that increases in incidence with age. We identified a profibrotic lung phenotype in aging mice characterized by an increase in the number of fibroblasts lacking the expression of thymocyte differentiation antigen 1 (Thy-1) and an increase in transforming growth factor (TGF)-β1 expression. It has been shown that Thy-1 expression can be epigenetically modified. Lung fibroblasts (PLFs) were treated with TGF-β1 ± DNA methyltransferase (DNMT) inhibitor 5-aza-2'-deoxycytidine (5-AZA) and analyzed for Thy-1 gene and protein expression, DNMT protein expression, and activity. α-Smooth muscle actin (α-SMA) and collagen type 1 (Col1A1) gene and protein expression was assessed. PLFs were transfected with DNMT1 silencing RNA ± TGF-β1. TGF-β1 inhibited Thy-1 gene and protein expression in PLFs, and cotreatment with 5-AZA ameliorated this effect and appeared to inhibit DNMT1 activation. TGF-β1 induced Thy-1 promoter methylation as assessed by quantitative methyl PCR. Treatment with 5-AZA attenuated TGF-β1-induced Col1A1 gene and protein expression and α-SMA gene expression (but not α-SMA protein expression). Inhibiting DNMT1 with silencing RNA attenuated TGF-β1-induced DNMT activity and its downstream suppression of Thy-1 mRNA and protein expression as well as inhibited α-SMA mRNA and Col1A1 mRNA and protein expression, and showed a decreased trend in Thy-1 promoter methylation. Immunofluorescence for α-SMA suggested that 5-AZA inhibited stress fiber formation. These findings suggest that TGF-β1 epigenetically regulates lung fibroblast phenotype through methylation of the Thy-1 promoter. Targeted inhibition of DNMT in the right clinical context might prevent fibroblast to myofibroblast transdifferentiation and collagen deposition, which in turn could prevent fibrogenesis in the lung and other organs.

Plasma LL-37 correlates with vitamin D and is reduced in human immunodeficiency virus-1 infected individuals not receiving antiretroviral therapy

Low levels of the vitamin D-regulated antimicrobial peptide cathelicidin (LL-37) may negatively impact the immune status of human immunodeficiency virus-1 (HIV-1) infected individuals (HIV+). We compared plasma LL-37 levels in healthy controls (HIV-) and HIV+ individuals on or off antiretroviral therapies (ARTs) (ART+ and ART-, respectively), and evaluated the relationship between vitamin D and LL-37 levels. In this cross-sectional study, levels of LL-37, 25-hydroxycholecalciferol [25(OH)D3] and 1,25-dihydroxycholecalciferol [1,25(OH)2D3] were measured from an initial cohort of 18 healthy controls and 10 HIV+/ART- individuals. Because this cohort lacked HIV+/ART+ subjects, LL-37 was also quantified from a second cohort of 10 HIV+/ART- and 13 HIV+/ART+ individuals. LL-37 levels were significantly lower in the HIV+/ART- group compared to the healthy controls (P = 0.01). A direct relationship was observed between LL-37 and both 25(OH)D3 and 1,25(OH)2D3. The level of 25(OH)D3 was predictive of higher LL-37 (P = 0.04) and for any given level of 25(OH)D3, HIV+/ART- subjects averaged 20 % lower LL-37 compared to the healthy controls (P = 0.045). For any given level of 1,25(OH)2D3, HIV+/ART- subjects averaged 25% lower LL-37 compared to the healthy controls (P = 0.018), although 1,25(OH)2D3 was not predictive of higher LL-37 (P = 0.28). Finally, LL-37 levels were significantly lower in the HIV+/ART- group compared to the HIV+/ART+ group from the second cohort (P = 0.045). Untreated HIV infection may contribute to lower LL-37 levels, independent of vitamin D levels. ART treatment may potentially mitigate this decrease in LL-37 levels.

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.

Bacterial pneumonia among HIV-infected patients: decreased risk after tobacco smoking cessation. ANRS CO3 Aquitaine Cohort, 2000-2007

BACKGROUND

Bacterial pneumonia is still a substantial cause of morbidity and mortality in HIV-infected patients in the era of combination Antiretroviral Therapy. The benefit of tobacco withdrawal on the risk of bacterial pneumonia has not been quantified in such populations, exposed to other important risk factors such as HIV-related immunodeficiency. Our objective was to estimate the effect of tobacco smoking withdrawal on the risk of bacterial pneumonia among HIV-infected individuals.

METHODOLOGY/PRINCIPAL FINDINGS

Patients of the ANRS CO3 Aquitaine Cohort with >or= two visits during 2000-2007 and without bacterial pneumonia at the first visit were included. Former smokers were patients who stopped smoking since >or= one year. We used Cox proportional hazards models adjusted on CD4+ lymphocytes (CD4), gender, age, HIV transmission category, antiretroviral therapy, cotrimoxazole prophylaxis, statin treatment, viral load and previous AIDS diagnosis. 135 cases of bacterial pneumonia were reported in 3336 patients, yielding an incidence of 12 per thousand patient-years. The adjusted hazard of bacterial pneumonia was lower in former smokers (Hazard Ratio (HR): 0.48; P = 0.02) and never smokers (HR: 0.50; P = 0.01) compared to current smokers. It was higher in patients with <200 CD4 cells/microL and in those with 200 to 349 CD4 cells/microL (HR: 2.98 and 1.98, respectively; both P<0.01), but not in those with 350 to 499 CD4 cells/microL (HR: 0.93; P = 0.79), compared to those with >or=500 CD4 cells/microL. The interaction between CD4 cell count and tobacco smoking status was not statistically significant.

CONCLUSIONS/SIGNIFICANCE

Smoking cessation dramatically reduces the risk of bacterial pneumonia, whatever the level of immunodeficiency. Smoking cessation interventions should become a key element of the clinical management of HIV-infected individuals.

Changing global epidemiology of pulmonary manifestations of HIV/AIDS

Tremendous advances have occurred in the care of patients with HIV/AIDS resulting from the advent of highly active antiretroviral therapy (HAART). This has led to differences in the presentations of HIV-related pulmonary disease. Infections such as bacterial pneumonias, particularly Streptococcus pneumoniae, remain commonplace, while opportunistic agents such as Pneumocystis jirovecii remain a concern in patients without adequate access to optimal medical care. The tuberculosis epidemic, once thought to be slowing, has been re-energized by the spread of HIV, particularly in sub-Saharan Africa. Unusual inflammatory responses due to a phenomenon of immune reconstitution, are now recognized as a consequence of HAART, with a reported incidence of IRIS in this setting ranges from 7 to 45% in retrospective reviews. Noninfectious pulmonary conditions such as chronic obstructive lung disease and pulmonary malignancies are gaining prominence as patients are accessing antiretroviral care and enjoying significantly extended survival.

Utilization of Fc receptors as a mucosal vaccine strategy against an intracellular bacterium, Francisella tularensis

Numerous studies have demonstrated that targeting Ag to Fc receptors (FcR) on APCs can enhance humoral and cellular immunity. However, studies are lacking that examine both the use of FcR-targeting in generating immune protection against infectious agents and the use of FcRs in the induction of mucosal immunity. Francisella tularensis is a category A intracellular mucosal pathogen. Thus, intense efforts are underway to develop a vaccine against this organism. We hypothesized that protection against mucosal infection with F. tularensis would be significantly enhanced by targeting inactivated F. tularensis live vaccine strain (iFt) to FcRs at mucosal sites, via intranasal immunization with mAb-iFt complexes. These studies demonstrate for the first time that: 1) FcR-targeted immunogen enhances immunogen-specific IgA production and protection against subsequent infection in an IgA-dependent manner, 2) FcgammaR and neonatal FcR are crucial to this protection, and 3) inactivated F. tularensis, when targeted to FcRs, enhances protection against the highly virulent SchuS4 strain of F. tularensis, a category A biothreat agent. In summary, these studies show for the first time the use of FcRs as a highly effective vaccination strategy against a highly virulent mucosal intracellular pathogen.

Detection of pulmonary Mycoplasma pneumoniae infections in HIV-infected subjects using culture and serology

OBJECTIVE

The true prevalence of Mycoplasma pneumoniae infections involving the respiratory tracts of HIV-infected individuals is still unclear. This study examined the prevalence of M. pneumoniae in 100 HIV-infected individuals at an AIDS care center in Chennai, India, using conventional laboratory techniques and interpretation criteria.

METHODS

Diagnosis was based on culture, cold agglutination test, and commercial enzyme-linked immunosorbent assay (ELISA) for the qualitative determination of IgM antibodies against M. pneumoniae. The efficacies of the different diagnostic procedures used in the study were analyzed.

RESULTS

The prevalence of M. pneumoniae was 31% by culture and 21% by IgM ELISA. Cough (p=0.03, OR 3.8, 95% CI 1-17.8), myalgia (p=0.04, OR 2.5, 95% CI 1-6.6), rales (p=0.04, OR 2.4, 95% CI 1-6.6), and cervical adenopathy (p=0.03, OR 2.7, 95% CI 1-7.1) were the symptoms that significantly corroborated culture positivity. Patients positive for M. pneumoniae by culture or IgM antibody had significantly greater CD4+ T-cell depletion and anemia than those without any evidence of infection.

CONCLUSIONS

This study provides the means to diagnose M. pneumoniae infection and information on the prevalence of the pathogen in HIV-infected individuals in resource constrained settings. Although modern molecular techniques may provide more insight into the prevalence of M. pneumoniae in HIV-infected individuals, conventional methods can still be used in diagnosis.

Seroprevalence of Mycoplasma pneumoniae in HIV-infected patients using a microparticle agglutination test

Mycoplasma pneumoniae is increasingly recognized as a common and important pathogen in community settings, and is responsible for various pulmonary and extrapulmonary conditions in the normal population. However, the seroepidemiology of acute M. pneumoniae infection in HIV-infected individuals is still unclear worldwide. This study examined the seroprevalence of antibodies to M. pneumoniae in HIV-infected patients admitted with respiratory complaints at a tertiary AIDS care centre in Chennai, India. A commercial gelatin microparticle agglutination test (Serodia-Myco II, Fujirebio) was used for the determination of antibodies against M. pneumoniae in acute serum specimens. Of the 200 HIV-infected patients with underlying pulmonary conditions tested, 34 (17 % positivity; 95 % CI 12-23 %) had antibodies specific to M. pneumoniae, while among the 40 patients with no underlying pulmonary symptoms, five (12.5 % positivity; 95 % CI 4-27 %) had evidence of anti-M. pneumoniae antibody. This shows that the incidence of M. pneumoniae seropositivity is greater in patients with underlying pulmonary complaints. Most positive titres were found in the age group 28-37 years in the symptomatic and symptom-free groups (64.7 and 60 %, respectively). The positive titres ranged from 40 to >20 480. High titres (> or =320) were found in 10 out of the 39 patients (25.6 %). This seroprevalence study reports a 16.2 % prevalence of M. pneumoniae infections in HIV-infected patients by a particle agglutination test.

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.

Serosurveillance of acute Mycoplasma pneumoniae infection among HIV infected patients with pulmonary complaints in Chennai, Southern India

BACKGROUND

The true seroepidemiology of acute Mycoplasma pneumoniae infection in HIV infected individuals is ambiguous.

METHODS

This study examined the serosurveillance of IgM antibodies to M. pneumoniae in HIV infected patients presenting with pulmonary symptoms at a tertiary AIDS care center in Chennai, Southern India, using cold-haemagglutination test and commercial enzyme linked immunosorbent assay in acute serum specimens.

RESULTS

One hundred HIV infected patients had enrolled in the study; 21 (21%) were positive for M. pneumoniae IgM antibodies by ELISA and 34 (34%) showed evidence of cold hemagglutinins.

CONCLUSION

This serosurveillance study reports a 21% prevalence of M. pneumoniae IgM antibody among HIV infected patients with pulmonary symptoms by ELISA and non-specific diagnosis was confirmed in 34% of the cases screened. Determination of cold agglutination titer could be used as a substitute to other expensive procedures in limited resource settings and third-world nations to diagnose M. pneumoniae infections for prompt initiation of therapy, as CAT has been found to be 100% sensitive and 84% specific in the diagnosis of M. pneumoniae infection.

Requirement of interleukin 17 receptor signaling for lung CXC chemokine and granulocyte colony-stimulating factor expression, neutrophil recruitment, and host defense

Bacterial pneumonia is an increasing complication of HIV infection and inversely correlates with the CD4(+) lymphocyte count. Interleukin (IL)-17 is a cytokine produced principally by CD4(+) T cells, which induces granulopoiesis via granulocyte colony-stimulating factor (G-CSF) production and induces CXC chemokines. We hypothesized that IL-17 receptor (IL-17R) signaling is critical for G-CSF and CXC chemokine production and lung host defenses. To test this, we used a model of Klebsiella pneumoniae lung infection in mice genetically deficient in IL-17R or in mice overexpressing a soluble IL-17R. IL-17R-deficient mice were exquisitely sensitive to intranasal K. pneumoniae with 100% mortality after 48 h compared with only 40% mortality in controls. IL-17R knockout (KO) mice displayed a significant delay in neutrophil recruitment into the alveolar space, and had greater dissemination of K. pneumoniae compared with control mice. This defect was associated with a significant reduction in steady-state levels of G-CSF and macrophage inflammatory protein (MIP)-2 mRNA and protein in the lung in response to the K. pneumoniae challenge in IL-17R KO mice. Thus, IL-17R signaling is critical for optimal production of G-CSF and MIP-2 and local control of pulmonary K. pneumoniae infection. These data support impaired IL-17R signaling as a potential mechanism by which deficiency of CD4 lymphocytes predisposes to bacterial pneumonia.

BAL and serum IgG levels in healthy asymptomatic HIV-infected patients

OBJECTIVES

To determine if the increased susceptibility to bacterial infection in asymptomatic HIV-infected patients is associated with decreased total IgG or IgG2 levels in lung epithelial lining fluid.

BACKGROUND

A decrease in lung IgG levels or subtypes has been proposed as contributing to the increased risk of bacterial lung infections in HIV-infected patients. Previous studies measuring lung lavage IgG concentrations have been inconsistent.

METHODS

Twenty-three HIV patients and 25 control subjects underwent BAL. Both patient groups were of similar age, and had similar pulmonary function studies and body mass index. Smokers were equally represented in both groups, and the majority of subjects in both groups were male. Total IgG and IgG2 levels in lavage fluid were assayed in both cohorts and compared using a two-tailed Student's t test.

RESULTS

The lung lining fluid IgG level in HIV-infected patients was 0.19 +/- 0.13 microg/microg of protein (mean +/- SD) vs 0.11 +/- 0.09 microg/microg of protein in control subjects (p < 0.05). The IgG(2) level in HIV patients was 0.034 +/- 0.038 microg/microg of protein and 0.014 +/- 0.01 microg/microg of protein in control subjects (p = 0.054). Lavage IgG levels reflected serum IgG values (correlation coefficient, 0.56; p < 0.001) but did not correlate with lung immunoglobulin-producing cells.

CONCLUSIONS

The increased susceptibility to bacterial pneumonia in asymptomatic HIV-infected individuals is neither explained by depressed total IgG levels nor a deficiency in IgG(2) levels in the lungs. The strong correlation between serum and lavage IgG levels suggests that lavage IgG derives from serum.

The growth and the control of human immunodeficiency virus in the lung: implications for highly active antiretroviral therapy

In recent years, it has become apparent that the lung is an important niche for the proliferation of human immunodeficiency virus (HIV), which may have implications for highly active antiretroviral therapy (HAART). The lung itself is a major site for the opportunistic infections associated with the progression to acquired immune deficiency syndrome (AIDS), specifically Pneumocystis carinii, Myobacterium tuberculosis and pyogenic bacteria. These cases of active pulmonary complications are direct indicators of enhanced progression to AIDS-defining illness and increased morbidity and mortality. It is therefore essential that the interaction between the lung and HIV is fully understood. Recent research indicates the lung may be a major sanctuary for the virus, with distinct evolution and replication in contrast to other target organs for HIV. In this review, we will discuss the recent findings of HIV infection, evolution, host factors involved in the control of HIV within the lung and the impact this may have on current therapy.