Phagocytosis and microbicidal capacity of human monocytes in the course of HIV infection

Microglia activation mediates fibrillar amyloid-β toxicity in the aged primate cortex

The amyloid-β peptide (Aβ) plays a central role in the pathogenesis of Alzheimer's disease (AD). The fibrillar form of Aβ (fAβ) exerts toxic effects on neurons through mechanisms not well understood. We have shown that the aged primate cortex is selectively vulnerable to fAβ toxicity at low concentrations. In addition to neuronal loss, fAβ induced massive activation of microglia in the aged rhesus cortex. We now demonstrate that inhibition of microglia activation abolishes fAβ toxicity. Injection or pump delivery of macrophage/microglia inhibitory factor (MIF) significantly reduced activation of microglia and the volume of damage caused by fAβ. Microglia isolated from aged rhesus cortex produced substantial reactive oxygen species when stimulated by fAβ, which was inhibited by MIF in a dose-dependent manner. This is the first definitive in vivo demonstration that the fAβ-induced microglia activation and inflammation mediate, at least in part, its toxic effects on neurons. Combined with our earlier observations, these findings suggest that aged primate microglia may display an exaggerated inflammatory response to fAβ when compared with young microglia.

Increase in the immunogenicity of HIV peptide antigens by chemical linkage to polytuftsin (TKPR40)

The use of synthetic peptide antigens in human prophylaxis still suffers from the very important problem of finding suitable carriers devoid of side effects. A desirable carrier for use in humans would be poorly immunogenic by itself, yet it would enhance the immune response to the peptide antigen. In the study reported herein, we examined the role of polytuftsin (TKPR40), a synthetic polymer of the natural immunomodulator tuftsin, as a carrier for synthetic peptides of HIV derived from the gp41 and gp120 proteins. Chimeric immunogens were constructed by chemical linkage between synthetic peptides of HIV and polytuftsin. These were employed for immunization of mice of different MHC haplotypes, and the humoral and cellular immune responses developed against the peptides were assessed by measuring total IgG, IgG, subclasses, T-cell proliferation, and in vitro cytokine release. A significantly stronger immune response was observed in mice immunized with the peptide-polytuftsin conjugates than in mice receiving the peptide dimers (peptide-peptide). Peptide-polytuftsin conjugates induced IgG2a and IgG2b isotype switching after both primary and secondary immunization. In addition, there was a positive correlation between the amounts of cytokines and the shift in the IgG isotypes. These data suggest that the use of polytuftsin as a carrier may increase the immune response against poorly immunogenic synthetic peptides.

The effects of HIV viral load on the phagocytic activity of monocytes activated with lipopolysaccharide from oral microorganisms

A study was undertaken to determine whether viral load status in HIV+ patients has any potential effect on monocyte phagocytic function both before and after challenge of the monocytes with lipopolysaccharide (LPS) isolated from oral microorganisms. LPS of two putative periodontal pathogens Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) was prepared. Whole blood samples in EDTA were collected from 30 HIV+ patients presenting for dental care at the University of Maryland. Control samples were prepared from appropriate uninfected individuals. Viral load was determined using quantitative RT-PCR (Amplicor, Roche Diagnostics). Phagocytic function was determined using FITC labeled Saccharomyces species in resting isolated monocytes and in cells after 24 h stimulation with 1 microgram/ml of LPS of P. gingivalis or F. nucleatum. Immunohistochemical staining was performed for complement receptor CR-1 (CD-35) on phagocyte cells. In HIV+ patients with high viral load (> 10,000 copies/ml), 13.5% of isolated resting monocytes demonstrated phagocytic activity, while 23% of the resting control monocytes from non-infected individuals showed phagocytic function. When the monocytes were stimulated with 1 microgram/ml of LPS of F. nucleatum, phagocytic activity was observed in 18.5% of monocytes in patients with high viral load, 33.5% with moderate viral load (400-10,00 copies/ml) and 51% with low viral load (<400 copies/ml), while 62% of the control monocytes demonstrated phagocytic activity. Stimulation of monocytes with LPS of P. gingivalis showed similar results. Complement receptor CD-35 showed a 50% decrease in expression in HIV+ patients with high viral load. A progressive decrease in monocyte/macrophage phagocytic function and CD-35 expression with and without oral LPS activation occurs after HIV infection and this trend appears to be accentuated in patients with high viral load. This relationship may contribute to increased susceptibility to oral opportunistic infections in advanced HIV+ patients.

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

The effects of colony stimulating factors on human monocyte cell function

We used a panel of functional assays to compare directly the pattern and potency of GM-CSF and M-CSF on monocyte activity associated with cell-mediated immune defense. GM-CSF and M-CSF were found to be equivalent both in their capacity to stimulate human monocyte functions in vitro and in their pattern of monocyte activation. The two CSFs were effective in inducing monocyte chemotaxis towards either fMLP or LTB4 at equivalent concentrations across a panel of donors. GM-CSF and M-CSF demonstrated equipotency in the induction of monocyte phagocytosis of heat-killed baker's yeast and in the regulation of the hexose-monophosphate shunt (NBT reduction). Both were also found to be equivalent in preventing steroid (dexamethasone)-induced suppression of monocyte anti-bacterial (Candida albicans) and anti-fungal (Staphylococcus aureus) phagocytic capacities. GM-CSF was somewhat more effective than M-CSF in stimulating monocyte C. albicans killing at a lower E:T ratio.