Cryptococcemia in primary HIV infection.

Opportunistic infections have been reported infrequently in primary HIV infection. We report a case of cryptococcemia in primary HIV infection. To our knowledge there has not been such a case reported. Our case highlights the need for clinicians to be wary of other opportunistic infections, including cryptococcosis, in primary HIV infection.

Acanthamoeba encephalitis: isolation of genotype T1 in mycobacterial liquid culture medium.

We report a case of Acanthamoeba encephalitis diagnosed from an antemortem brain biopsy specimen, where the organism was first isolated in mycobacterial liquid medium and first identified by using a sequence generated by a commercial panfungal sequencing assay. We correlate susceptibility results with clinical outcome.

Impaired complement-mediated phagocytosis by HIV type-1-infected human monocyte-derived macrophages involves a cAMP-dependent mechanism.

HIV-1 infection of cells of macrophage lineage impairs a number of effector functions performed by these cells, including phagocytosis of opsonized pathogens. In this study we investigate the effects of HIV-1 on the mechanism of complement (C')-mediated phagocytosis by human monocyte-derived macrophages (MDM). Using C'-opsonized sheep red blood cells (sRBC) as targets, we demonstrate that phagocytosis is inhibited by HIV-1 infection in vitro. Inhibition is not due to downregulation of surface C' receptors (R) or altered binding of C'-opsonized targets to HIV-1-infected MDM, suggesting a postreceptor-mediated mechanism of suppression. Having shown that increased levels of intracellular cAMP in uninfected MDM inhibit phagocytosis, we demonstrate that HIV-1 infection of MDM is associated with increased intracellular cAMP. Using the adenylate cyclase inhibitors 2',5'-dideoxyadenosine and MDL-12,330A, we show that phagocytosis by HIV-1- infected MDM can be restored by inhibition of cAMP production. Defective phagocytosis by HIV-1-infected MDM did not correlate with prostaglandin secretion, and was less in uninfected MDM within the HIV-1-infected cell culture suggesting a minimal bystander effect. Inhibition required viral entry but not active viral replication, as shown by use of the antiretroviral drug lamivudine. Hence, our study suggests that HIV-1 impairs C'R-mediated phagocytosis in MDM by elevating intracellular cAMP levels, independent of prostaglandin secretion, and contributes to our understanding of how HIV-1 impairs cell-mediated immunity.

Adverse effects of antiretroviral drugs on HIV-1-infected and -uninfected human monocyte-derived macrophages.

Antiretroviral drugs approved for treatment of HIV-1 infection include nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs). Use of these drugs in combinations (highly active antiretroviral therapy) has delayed disease progression. However, long-term therapy is associated with potentially serious adverse effects. NRTIs are thought to contribute to these adverse effects via depletion of mtDNA. Inasmuch as macrophages (major targets for HIV-1) are highly metabolically active with large numbers of mitochondria, we investigated the effects of NRTIs (didanosine, stavudine, lamivudine, and zidovudine) on the viability and function of HIV-1-infected and -uninfected human monocyte-derived macrophages (MDMs). We demonstrate that the combinations didanosine/stavudine and lamivudine/zidovudine decrease mtDNA content in MDMs, with HIV-1-infected MDMs displaying a greater reduction than uninfected cells. This decrease correlated with decreased complement-mediated phagocytosis (C'MP) by MDMs, a process dependent on mitochondrial function. Inasmuch as PIs have previously been reported to interact with cellular proteases and given that cellular proteases are involved in the phagocytic process, we investigated the effects of the PI indinavir on C'MP. We demonstrate that indinavir augments C'MP by uninfected MDMs, but not HIV-1-infected MDMs. This study provides additional understanding on the effects of commonly used antiretroviral drugs on cellular immune function.

Phagocytosis stimulates mobilization and shedding of intracellular CD16A in human monocytes and macrophages: inhibition by HIV-1 infection.

Surface and intracellular staining coupled with flow cytometric analysis was used to show for the first time that human macrophages and a minor subset of peripheral blood monocytes have an internal pool of CD16A, which is mobilized and shed during Fc receptor for immunoglobulin G-mediated phagocytosis. Human immunodeficiency virus type 1 (HIV-1) infection of monocyte-derived macrophages in vitro led to a reduction in the phagocytosis-induced up-regulation in CD16A shedding. These results suggest that monocytes and macrophages may be a source of soluble CD16A, which is elevated in the serum of patients in a variety of disease states and that the mobilization and shedding of CD16A in response to phagocytosis are disrupted by HIV-1 infection.

Phagocytic efficiency of monocytes and macrophages obtained from Sydney blood bank cohort members infected with an attenuated strain of HIV-1.

Defective function of monocyte-derived macrophages contributes to HIV-1 pathogenesis. We found that phagocytosis of the opportunistic pathogens Mycobacterium avium complex and Toxoplasma gondii was impaired in monocytes obtained from individuals infected with wild-type strains of HIV-1 but generally not in monocytes collected over a 6-year period from Sydney Blood Bank Cohort (SBBC) members infected with nef/long terminal repeats (LTR) region-defective strains of HIV-1. However, longitudinal analysis of phagocytosis in 1 SBBC member, C54, showed the development of defective engulfment of opportunistic pathogens at the most recent time points, coincident with the development of further molecular deletions in the nef/LTR region. Another SBBC member, C98, underwent bronchoscopy, which provided material to examine phagocytic signaling in alveolar macrophages. In contrast to normal phagocytic efficiency of C98's monocytes (over a 6-year period), defective signaling events during FcgammaR-mediated phagocytosis by C98's alveolar macrophages were observed. High basal phosphorylation within HIV-infected macrophages correlated with colocalization of tyrosine-phosphorylated proteins with HIV-1 p24 antigen rather than around the phagocytic targets as observed in uninfected cells. Thus, although phagocytic efficiency appears to be generally unimpaired in monocytes from SBBC members, evidence of impairment in recent samples from 1 SBBC member, coincident with further genetic changes within the virus, and abnormal phagocytic signaling in alveolar macrophages from another SBBC member may herald loss of attenuation of those strains.

Defective phagocytosis by human monocyte/macrophages following HIV-1 infection: underlying mechanisms and modulation by adjunctive cytokine therapy.

Defective immunological function of cells of the macrophage lineage contributes considerably to the pathogenesis of HIV-1 infection. Impairment of phagocytosis of opportunistic pathogens such as Mycobacterium avium complex (MAC), Pneumocystis carinii, Toxoplasma gondii or Candida albicans by peripheral blood monocytes, tissue macrophages and monocyte-derived macrophages following in vivo and in vitro HIV-1 infection is well documented. The development of opportunistic infections due to these pathogens in HIV-infected individuals at late stages of disease is attributed to defective monocyte/macrophage function. The mechanisms whereby HIV-1 impairs phagocytosis are not well known. A number of phagocytic receptors normally mediate engulfment of specific opportunistic pathogens by cells of macrophage lineage; distinct mechanisms are triggered by pathogen-receptor binding to promote cytoskeletal rearrangements and engulfment. This review focuses on the signalling events occurring during Fcgamma receptor- and complement receptor-mediated phagocytosis, and considers the mechanisms by which HIV-1 inhibits those signalling events. Since macrophage function is enhanced by cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-gamma (IFN-gamma), the use of these immunomodulators is of potential interest as adjunctive immunotherapy in immunosuppressed individuals. In this review we present examples of clinical applications of GM-CSF and IFN-gamma therapy for the treatment of opportunistic infections in HIV-infected individuals receiving antiretroviral drugs.