Increased expression and occupancy of receptors for tumour necrosis factor on blood monocytes from tuberculosis patients

Mycobacterium avium subspecies paratuberculosis infection of cattle does not diminish peripheral blood-derived macrophage mycobactericidal activity

Ruminants infected with Mycobacterium avium subspecies paratuberculosis consistently develop a multibacillary form of disease that is centered on the ileum. Mechanisms responsible for failure of macrophage function during multibacillary disease are incompletely characterized. Our data suggest that mycobactericidal functions are present, and potentially enhanced, in monocyte-derived macrophages from M. avium subsp. paratuberculosis infected cattle. Addition of CD4(+) T cells from infected animals to autologous in vitro infected macrophages did not increase bacterial killing. In contrast, CD4(+) T cells from non-infected animals did increase bacterial killing in autologous macrophages. In macrophages from both infected and non-infected cattle, bacterial killing appeared to be independent of interferon-gamma (IFN-gamma) and nitric oxide production.

The 75-kD tumour necrosis factor (TNF) receptor is specifically up-regulated in monocytes during Q fever endocarditis

Q fever is an infectious disease caused by Coxiella burnetii, an obligate intracellular microorganism that inhabits monocytes/macrophages. The dysregulated production of TNF-alpha in Q fever endocarditis has been associated with defective killing of C. burnetii by patient monocytes. As soluble receptors for TNF-alpha (TNF-R55 and TNF-R75) regulate TNF-alpha activity, we investigated their release by monocytes in Q fever. Spontaneous and C. burnetii-stimulated release of TNF-R75, but not of TNF-R55, was up-regulated in patients with ongoing endocarditis compared with controls. The increase in TNF-R75 release was related to the activity of Q fever endocarditis, since TNF-R75 release was similar in patients with cured endocarditis and controls. While spontaneous release of TNF-R75 by monocytes from patients with ongoing Q fever endocarditis occurred without changes in its membrane expression, C. burnetii increased the surface expression of TNF-R75. In addition, TNF-R75 transcripts were increased in resting and C. burnetii-stimulated monocytes from patients with ongoing endocarditis. On the other hand, TNF-R75 release was not related to TNF-alpha secretion. These results indicate that the modulation of TNF-R75 is a critical feature of the pathophysiology of Q fever endocarditis.

Examining a paradox in the pathogenesis of human pulmonary tuberculosis: immune activation and suppression/anergy

Protective immunity against Mycobacterium tuberculosis (MTB) in animal models is based on cell-mediated immunity (CMI), involving bi-directional interactions between T cells and cells of the monocyte/macrophage (MO/MA) lineage. Key factors include MO-derived interleukin (IL)-12 and tumor necrosis factor (TNF)-alpha as well as T cell derived IL-2 and interferon (IFN)-gamma. These cytokines appear particularly crucial in the induction of MA-mediated elimination of mycobacteria. Several lines of evidence indicate that similar mechanisms are operating in humans. During active pulmonary tuberculosis (PTB), signs of both immune depression and immune activation are concomitantly present. Decreased tuberculin skin test reactivity in vivo and deficient IFN-gamma production by MTB-stimulated mononuclear cells in vitro are observed. On the other hand, the serum levels of several cytokines, including TNF, and other inflammatory mediators are increased and circulating MO and T cell show phenotypic and functional evidence of in vivo activation. In this review, we will discuss the evidence for three models, which could explain this apparent paradox: 1. Stimulation of the T cell-suppressive function from MO/MA; 2. Intrinsic T cell refractoriness, possibly associated with tendency to apoptosis (programmed cell death), and 3. Compartmentalization and redistribution of immune responses to the site of disease. The opportunistic behavior of MTB during human immunodeficiency virus (HIV) infection can be explained by suppression of type-1 responses at the level of antigen-presenting cells, CD4 T cells and effector macrophages. The ominous prognostic significance of intercurrent PTB during HIV infection seems primarily due to prolonged activation of HIV replication in macrophages. Supportive immune therapy during PTB could aim at correcting the type-1 deficiency either by IFN-gamma inducers (e.g. IL-12, IL-18) or by neutralizing the suppressive cytokines transforming growth factor beta (TGF-beta) and IL-10. Alternatively, inflammatory over-activity could be reduced by neutralizing TNF. Finally, anti-apoptotic therapies (e.g. IL-15) might be considered.

Thalidomide reduces tumour necrosis factor-alpha production by human alveolar macrophages

Overexuberant production of tumour necrosis factor-alpha (TNF-alpha) by macrophages and other cells is thought to contribute to the development of permanent lung damage in many inflammatory conditions. There is a need for an agent, without the side-effects of corticosteroids, which can reduce the production of TNF-alpha by macrophages activated by disease. This study evaluated the effect of thalidomide on lipopolysaccharide (LPS)-induced TNF-alpha production by human alveolar macrophages obtained from patients with tuberculosis and a group of other diseases associated with macrophage activation. Alveolar macrophages obtained by bronchoalveolar lavage from 31 patients (tuberculosis = 12, sarcoidosis = 3, lung cancer = 5, chronic bronchitis = 5, pneumonia = 6) were stimulated with LPS alone or LPS in combination with either thalidomide or dexamethasone. Cell-associated TNF-alpha, as measured by immunochemistry, and TNF-alpha released by macrophages, as assessed by ELISA, were markedly increased when cells were incubated with LPS (P < 0.05), and both were decreased following addition of thalidomide (P < 0.05) or dexamethasone (P < 0.05) to amounts similar to those observed when macrophages were incubated with medium alone. Similarly, TNF-alpha mRNA as measured by in situ hybridization was increased following incubation with LPS (P < 0.05), but this increase was prevented by addition of thalidomide (P < 0.05) or dexamethasone (P < 0.05). The ability of thalidomide to reduce LPS-induced TNF-alpha production by alveolar macrophages was the same when cells from patients with tuberculosis (a disease associated with TNF-alpha production) and cells from patients with the other conditions were compared. The ability of thalidomide to reduce TNF-alpha production by human alveolar macrophages from patients with active lung disease suggests that thalidomide and its analogues may have potential as drugs to reduce TNF-alpha production in disease.

Modulation of monocyte antigen-presenting capacity by tumour necrosis factor-alpha (TNF): opposing effects of exogenous TNF before and after an antigen pulse and the role of TNF gene activation in monocytes

We have previously shown that exogenous human recombinant tumour necrosis factor-alpha (rTNF), added before an antigen pulse, enhanced antigen presentation by human blood monocytes. The present study shows that, surprisingly, rTNF added after an antigen (PPD) pulse inhibited, while anti-TNF monoclonal antibody (mAb) enhanced, antigen presentation. mAbs htr-9 against p55 TNF receptor type I (TNF-RI) abrogated rTNF enhancing effect on PPD presentation and decreased presenting activity of untreated monocytes while utr-1 mAb, against p75 TNF receptor type II (TNF-RII), reversed the inhibitory effect of rTNF given after antigen pulse. PPD and rTNF when added singly induced TNF-mRNA accumulation in monocytes. Pretreatment of monocytes with rTNF followed by a PPD pulse caused an enhancement of TNF-mRNA accumulation. However, when post-treatment with rTNF was applied to PPD-pulsed monocytes, then inhibition of TNF gene expression was seen. This may point to the role of endogenously generated TNF in regulation of antigen-presenting capacity of monocytes. These studies indicate that TNF is an important regulator of monocyte antigen-presenting capacity and that the level of TNF gene activation in monocytes may be associated with their ability to present nominal antigen.

Altered expression of CD11/CD18 on the peripheral blood phagocytes of patients with tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis, is characterized by granulomatous lesions made up of epithelioid cells, giant cells and mononuclear leucocytes. Cell-cell adhesion is important in granuloma formation and in the leucocyte migration which accompanies it. We have recently shown increased expression of the adhesion molecules CD11/CD18 (LeuCAMs, beta 2 integrins) on peripheral blood leucocytes from patients with sarcoidosis (Shakoor & Hamblin, 1992). Here we have studied the expression of CD11/CD18 and CD29 (VLA beta 1 integrin) on the peripheral blood leucocytes of 10 TB patients by flow cytometry. The density (expressed as mean fluorescence intensity) of CD11b on monocytes and polymorphs was increased (P < 0.005), as was CD11c (P < 0.005) and CD18 (P < 0.05) on polymorphs. CD11a expression was significantly reduced on polymorphs (P < 0.05). No differences were found in the expression of CD29, the percentages of cells expressing any molecule and, in contrast to sarcoidosis, the density of any molecule on lymphocytes. Although the cytokine tumour necrosis factor (TNF) has been implicated in the process of up-regulation, an ELISA for TNF failed to detect significant levels in plasma. The results suggest increased peripheral phagocyte CD11/CD18 expression is a feature of TB, which may contribute to the pathological processes involved.