Role of T cell subsets in the modulation of Mycobacterium avium growth within human monocytes

Safety and efficacy of treatment using interleukin-2 in a patient with idiopathic CD4(+) lymphopenia and Mycobacterium avium-intracellulare

We present the case of a 39-year-old white man with a Myobacterium avium-intracellulare pulmonary infection found to have a CD4(+) count of 172 cells/mm(3) and diagnosed subsequently with idiopathic CD4(+) lymphopenia (ICL). After receiving clathromycin for 4 months with minimal improvement, the patient was started on pegylated subcutaneous interleukin (IL)-2 at 600,000 units daily. Later, he received incrementally higher pegylated IL-2 doses until he reached a maintenance dose 3 months later of 11 million units weekly divided into three equal doses. After 5 months of therapy, the patient's chronic cough resolved completely, sputum cultures became negative for Myobacterium avium-intracellulare and the CD4(+) T cell count increased to 553 cells/mm(3). After 35 months of well-tolerated IL-2 treatments and no recurrence of any opportunistic infections, IL-2 treatment was stopped. CD4(+) counts 6 and 9 months after discontinuing IL-2 treatment were 596 and 378 cells/mm(3) respectively, and he remains asymptomatic. This report supports IL-2 treatment for ICL-associated opportunistic infections as a safe and potentially efficacious treatment option, especially when combined with more traditional treatment regimens.

Toll-like receptor genes are differentially expressed at the sites of infection during the progression of Johne's disease in outbred sheep

Toll-like receptors (TLR) are engaged by ligands on microbial pathogens to initiate innate and adaptive immune responses. Little is known about TLR involvement during infection with Mycobacterium avium subsp. paratuberculosis (M. ptb), the cause of Johne's disease in ruminants, although there is a profound immunopathological response in affected animals. We have analyzed the expression of 10 TLR genes relative to validated reference genes at predilection sites in ileum, jejunum and associated lymph nodes as well as in peripheral blood, to determine if TLR expression is altered in response to infection with M. ptb in outbred sheep. Previously unexposed animals from two flocks and animals from three naturally infected flocks were used with restricted maximum likelihood linear mixed modeling applied to determine significant differences. These were related to the pathologies observed at different stages of infection in exposed sheep, after allowing for other sources of variation. In most cases there were differences in TLR expression between early paucibacillary and multibacillary groups when compared to uninfected sheep, with most TLRs for the paucibacillary group having lower expression levels than the multibacillary group. Increased expression of TLR1-5, and 8 was observed in ileum or jejunum, and TLR1-4, 6, and 8 in mesenteric lymph nodes. There was a trend for increased expression of TLR1, 2, and 6-8 in PBMCs of exposed compared to non-exposed animals. Further study of TLR expression in Johne's disease in ruminants is warranted as these observed differences may help explain pathogenesis and may be useful in the future diagnosis of M. ptb infection.

Activation of p38 MAPKalpha by extracellular pressure mediates the stimulation of macrophage phagocytosis by pressure

We have previously demonstrated that constant 20 mmHg extracellular pressure increases serum-opsonized latex bead phagocytosis by phorbol 12-myristate 13-acetate (PMA)- differentiated THP-1 macrophages in part by inhibiting focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Because p38 MAPK is activated by physical forces in other cells, we hypothesized that modulation of p38 MAPK might also contribute to the stimulation of macrophage phagocytosis by pressure. We studied phagocytosis in PMA-differentiated THP-1 macrophages, primary human monocytes, and human monocyte-derived macrophages (MDM). p38 MAPK activation was inhibited using SB-203580 or by p38 MAPKalpha small interfering RNA (siRNA). Pressure increased phagocytosis in primary monocytes and MDM as in THP-1 cells. Increased extracellular pressure for 30 min increased phosphorylated p38 MAPK by 46.4 +/- 20.5% in DMSO-treated THP-1 macrophages and by 20.9 +/- 9% in primary monocytes (P < 0.05 each). SB-203580 (20 microM) reduced basal p38 MAPK phosphorylation by 34.7 +/- 2.1% in THP-1 macrophages and prevented pressure activation of p38. p38 MAPKalpha siRNA reduced total p38 MAPK protein by 50-60%. Neither SB-203580 in THP-1 cells and peripheral monocytes nor p38 MAPK siRNA in THP-1 cells affected basal phagocytosis, but each abolished pressure-stimulated phagocytosis. SB-203580 did not affect basal or pressure-reduced FAK activation in THP-1 macrophages, but significantly attenuated the reduction in ERK phosphorylation associated with pressure. p38 MAPKalpha siRNA reduced total FAK protein by 40-50%, and total ERK by 10-15%, but increased phosphorylated ERK 1.4 +/- 0.1-fold. p38 MAPKalpha siRNA transfection did not affect the inhibition of FAK-Y397 phosphorylation by pressure but prevented inhibition of ERK phosphorylation. Changes in extracellular pressure during infection or inflammation regulate macrophage phagocytosis by a FAK-dependent inverse effect on p38 MAPKalpha that might subsequently downregulate ERK.

Mycobacterium avium infection and modulation of human macrophage gene expression

Mycobacterium avium is a facultative intracellular pathogen cleared rapidly via intact host defense mechanisms. In the absence of adequate T cell function, as occurs in HIV-1-induced immunodeficiency, M. avium becomes an opportunistic infection with uncontrolled replication and reinfection of macrophage hosts. How M. avium infects, survives, and replicates in macrophages without signaling an effective microbicidal counterattack is unresolved. To address whether M. avium signals the expression of molecules, which influence mycobacterial survival or clearance, human monocyte-derived macrophage cultures were exposed to M. avium. Within minutes, M. avium, or its cell wall lipoarabinomannan, binds to the adherent macrophages and induces a spectrum of gene expression. In this innate response, the most abundant genes detected within 2 h by cDNA expression array involved proinflammatory chemokines, cytokines including TNF-alpha and IL-1, and adhesion molecules. Associated with this rapid initial up-regulation of recruitment and amplification molecules was enhanced expression of transcription factors and signaling molecules. By 24 h, this proinflammatory response subsided, and after 4 days, when some bacteria were being degraded, others escaped destruction to replicate within intracellular vacuoles. Under these conditions, inducible NO synthase was not up-regulated and increased transferrin receptors may facilitate iron-dependent mycobacterial growth. Sustained adhesion molecule and chemokine expression along with the formation of multinucleated giant cells appeared consistent with in vivo events. Thus, in the absence of T lymphocyte mediators, macrophages are insufficiently microbicidal and provide a nonhostile environment in which mycobacteria not only survive and replicate, but continue to promote recruitment of new macrophages to perpetuate the infection.

Expression of IL-18 by Mycobacterium avium-infected human monocytes; association with M. avium virulence

Disseminated Mycobacterium avium infection is the most frequent bacterial infection in patients with advanced AIDS and also associated with interferon-gamma (IFN-gamma) or IL-12 receptor deficiency. IFN-gamma is a key cytokine in host defence against M. avium infection. Expression of IL-18, a potent IFN-gamma inducer, and IFN-gamma by human monocytes after infection with M. avium was examined. Monocytes were co-cultured with isogenic smooth-transparent (SmT: virulent) or smooth-domed (SmD: avirulent) M. avium strains (10 organisms per monocyte). Infection with the SmD strain induced significantly higher concentration of IL-18 and IFN-gamma in culture supernatants than did the SmT strain. IFN-gamma production in response to M. avium was partially inhibited by anti-human IL-18 MoAb. Both recombinant human IL-12 (77 +/- 42 pg/ml, control versus 1492 +/- 141 pg/ml, cultures with IL-12 1 ng/ml) and IL-18 (126 +/- 37 pg/ml, control versus 2683 +/- 864 pg/ml, cultures with IL-18 10 ng/ml) augmented M. avium-induced IFN-gamma production. Freshly isolated uninfected monocytes expressed constitutive levels of IL-18. Following infection with M. avium, enhancement of IL-18 mRNA expression peaked at 3-6 h. IL-18 protein was detected in monocyte lysates as early as 1 h after infection with both SmT and SmD M. avium strains by Western blotting. Higher IL-18 expression by monocytes infected with the avirulent strain may result in more IFN-gamma production, thus modulating its pathogenicity. Local induction of IL-18 may be important both for M. avium pathogenicity and host defence and become a potential candidate for immunotherapy.