Nocardia fractions, NLD and NWSM, induce tumor necrosis factor-alpha secretion in human monocytes: role of protein kinase C

Early intracellular trafficking of Waddlia chondrophila in human macrophages

Waddlia chondrophila is an obligate intracellular bacterium considered as a potential agent of abortion in both humans and bovines. This member of the order Chlamydiales multiplies rapidly within human macrophages and induces lysis of the infected cells. To understand how this Chlamydia-like micro-organism invades and proliferates within host cells, we investigated its trafficking within monocyte-derived human macrophages. Vacuoles containing W. chondrophila acquired the early endosomal marker EEA1 during the first 30 min following uptake. However, the live W. chondrophila-containing vacuoles never co-localized with late endosome and lysosome markers. Instead of interacting with the endosomal pathway, W. chondrophila immediately co-localized with mitochondria and, shortly after, with endoplasmic reticulum- (ER-) resident proteins such as calnexin and protein disulfide isomerase. The acquisition of mitochondria and ER markers corresponds to the beginning of bacterial replication. It is noteworthy that mitochondrion recruitment to W. chondrophila inclusions is prevented only by simultaneous treatment with the microtubule and actin cytoskeleton-disrupting agents nocodazole and cytochalasin D. In addition, brefeldin A inhibits the replication of W. chondrophila, supporting a role for COPI-dependent trafficking in the biogenesis of the bacterial replicating vacuole. W. chondrophila probably survives within human macrophages by evading the endocytic pathway and by associating with mitochondria and the ER. The intracellular trafficking of W. chondrophila in human macrophages represents a novel route that differs strongly from that used by other members of the order Chlamydiales.

Waddlia chondrophila enters and multiplies within human macrophages

Waddlia chondrophila is an obligate intracellular bacterium of the Chlamydiales order. W. chondrophila has been isolated twice from aborted bovine foetuses and a serological study supported the abortigenic role of W. chondrophila in bovine species. Recently, we observed a strong association between the presence of anti-Waddlia antibodies and human miscarriage. To further investigate the pathogenic potential of W. chondrophila in humans, we studied the entry and the multiplication of this Chlamydia-like organism in human macrophages. Confocal and electron microscopy confirmed that W. chondrophila is able to enter human monocyte-derived macrophages. Moreover, W. chondrophila multiplied readily within macrophages. The proportion of infected macrophages increased from 13% at day 0 to 96% at day 4, and the mean number of bacteria per macrophage increased by 3logs in 24h. Intracellular growth of W. chondrophila was associated with a significant cytopathic effect. Thus, W. chondrophila may enter and grow rapidly within human macrophages, inducing lysis of infected cells. Since macrophages are one of the major components of the innate immune response, these findings indirectly suggest the possible human pathogenicity of W. chondrophila.

Fumonisin B1-induced apoptosis is associated with delayed inhibition of protein kinase C, nuclear factor-kappaB and tumor necrosis factor alpha in LLC-PK1 cells

Fumonisin B1 (FB1), the most potent of the fumonisin mycotoxins, is a carcinogen and causes a wide range of species-specific toxicoses. FB1 modulates the activity of protein kinase C (PKC), a family of phospholipid-dependent serine/threonine kinases that play important role in modulating a variety of biologic responses ranging from regulation of cell growth to cell death. Although it has been demonstrated that FB1 induces apoptosis in many cell lines, the precise mechanism of apoptosis is not fully understood. In this study, we investigated the membrane localization of various PKC isoforms, PKC enzyme activity, and its downstream targets, namely nuclear factor-kappa B (NF-kappaB), tumor necrosis factor alpha (TNFalpha), and caspase 3, in porcine renal epithelial (LLC-PK1) cells. FB1 repressed cytosol to membrane translocation of PKC-alpha, -delta, -epsilon, and -zeta isoforms over 24-72 h. The FB1-induced membrane PKC repression was corroborated by a concentration-dependent decrease in total PKC activity. Exposure of cells to phorbol 12-myristate 13-acetate (PMA) for this duration also resulted in repressed PKC membrane localization and activity comparable to FB1. Exposure of cells to FB1 (10 microM) was associated with inhibition of cytosol to nuclear translocation of NF-kappaB and NF-kappaB-DNA binding at 72 h. The expression of TNFalpha was significantly inhibited at 24 and 48 h in response to 1 and 10 microM FB1. Increased caspase 3 activity was observed in LLC-PK1 cells exposed to > or =1 microM FB1 at 48 h. PMA also increased the caspase 3 activity at 24 and 48 h. Results suggest that FB1-induced apoptosis involves the activation of caspase 3, which is associated with the repression of PKC and possibly its down-stream effectors, NF-kappaB and TNFalpha.

Occurrence and specificity of human natural and in vitro induced antibodies to Nocardia opaca antigens

Nocardia opaca, a Gram-positive bacterium, is a potent source of immunostimulatory substances. Screening of sera of adult human donors revealed that all sera tested contained antibodies reactive with isolated Nocardia fractions (Nocardia delipidated cell mitogen, NDCM; Nocardia lysozyme digest, NLD; Nocardia water-soluble mitogen, NWSM; and fraction B). The respective values of reciprocal titres for IgM and IgG were in the range of 100 to 12,800, and 10 to 320 for IgA antibody isotypes, when NLD or fraction B were used as antigens in enzyme-linked immunosorbent assay (ELISA) tests. The level of antibodies directed to NDCM, a potent polyclonal B cell activator, was found to be the lowest. In vitro spontaneous as well as NDCM-induced production of antibodies to NDCM by human peripheral blood lymphocytes involved mainly the IgM class. Western-blot analysis demonstrated that antibodies in normal human sera react with nocardial antigens of molecular mass approximately 60, 40, 20 and 15-10 kDa. The same antigens were also recognized by rabbit and mouse hyperimmune sera, also confirming the immundominancy of these nocardial antigens in other species. The presence of anti-nocardia antibodies in human sera and their production by both stimulated and non-stimulated lymphocytes points to the natural sensitization of humans either by ubiquitous no-cardial components or by cross-reactive bacterial or food antigens.

Upregulation of tumor necrosis factor alpha and interleukin-1 beta in Q fever endocarditis

The occurrence of Q fever endocarditis likely involves some alterations in the responses of monocytes, the in vivo targets of Coxiella burnetii. To test this hypothesis, the production of the inflammatory cytokines tumor necrosis factor alpha, interleukin-1 beta, and interleukin-6 was assessed in monocytes from patients with Q fever endocarditis. Spontaneous transcription and secretion of tumor necrosis factor and interleukin-1 were significantly higher in patient monocytes than in healthy controls. The interleukin-6 transcripts were also upregulated in patient cells. Moreover, in patients with recent endocarditis exhibiting high titers of immunoglobulin G directed to C. burnetii in phase I, monocytes released significantly higher levels of tumor necrosis factor and interleukin-1 than in patients with stabilized endocarditis. Immunoglobulin G titers and the overproduction of tumor necrosis factor and interleukin-1 were significantly correlated. Hence, the overproduction of inflammatory cytokines might be a marker of disease activity.

Expression of TNF-alpha in pig fetal cells stimulated in vitro

Macrophages and lymphocytes of pig fetuses stimulated in vitro with bacterial mitogens such as lipopolysaccharide and Nocardia opaca delipidated cell mitogen showed a high TNF-alpha cytoplasmic expression. TNF-alpha was detected by immunofluorescence in peripheral blood lymphocytes and lymphocytes from the thymic region as early as at 34 d of gestation. Macrophages were the main producers of TNF-alpha at later developmental stages.

Immunomodulation by bacterial fractions

The cells of Nocardia opaca are a source of potent immunostimulating substances, differing in solubility and in the presence or absence of peptidoglycan. Three classes of N. opaca fractions have been investigated: (1) NDCM (Nocardia delipidated cell mitogen), the starting fraction; (2) PG (peptidoglycan)-containing fractions: CW (cell walls), PG, and fractions containing soluble PG derivatives such as NWSM (Nocardia water soluble mitogen) and NSPD (Nocardia soluble peptidoglycan derivative); and (3) soluble fractions devoid of PG, such as NWSMP (NWSP-pellet) and CyI (cytoplasmic membrane). This report summarizes our results on the relationship between the structure of N. opaca fractions and their stimulatory activities on mouse, rabbit, germ-free piglet and human lymphocytes and monocytes/macrophages. The studies of biological properties of these compounds are the result of an extensive collaborative effort of several teams.

Treatment of radiation disease by Nocardia fraction: possible effect of inflammatory cytokines

Nocardia delipidated cell mitogen (NDCM) derived from Nocardia opaca, given 2 h after whole-body gamma irradiation (2.5 Gy) to germ-free piglets in amounts of 1 mg/kg via a stomach tube, prevented the loss of B-cells in the spleen, intestinal mucosa, and mesenteric lymph nodes when recorded on day 8 after irradiation. NDCM and/or formolized Enterococcus faecalis strain (Ef) applied intraperitoneally also 2 h after irradiation increased the survival rate in mice irradiated with 8.3 Gy and 8.5 Gy doses. The number of nucleated bone marrow cells and the content of RNA in the spleen were significantly higher in rats given immunostimulators NDCM and Ef after irradiation with 5.0 Gy. The effect is presumed to be a consequence of stimulated production of inflammatory cytokines.

Protein tyrosine kinases and TNF alpha secretion in human monocytes

The role of protein tyrosine kinases (PTK) in TNF alpha secretion by human monocytes was investigated in this report. We showed that an immunomodulator such as Nocardia lysozyme digest (NLD) and a particulate agonist, zymosan, stimulated an increase in tyrosine phosphorylation of several endogenous substrates including 53-56 kDa protein which was the predominant phosphoprotein. In addition, NLD and zymosan induced TNF alpha secretion which was impaired by a PTK inhibitor, tyrphostin. We suggest that a cascade of kinases including PTK is involved in NLD and zymosan signalling.