Why does tuberculosis lead to specific inflammation?

When Mycobacterium tuberculosis infects humans, about 20% of those infected actually develop tuberculosis (TB). In Japan, the incidence of TB in 2008 was 24,760 cases (19.4/100,000 persons) and the rate has been decreasing gradually, but is still higher than in the USA, Holland, and Belgium, for example. Histologically, tuberculosis displays exudative inflammation, proliferative inflammation and productive inflammation depending on the time course. In productive inflammation, granulomatous lesions with necrotic centers are formed. The typical granulomas consist of epithelioid macrophages, Langhans' multinucleated giant cells, lymphocytes and fibroblasts, and the process of their formation involves many cytokines, chemokines and transcription factors. These findings have been derived primarily from animal experiments utilizing an airborne infection apparatus. The conditions for airborne infection have been described in detail elsewhere. This mini-review focuses on what has been found through animal experiments, and also indicates areas for which data are not currently available.

Hypothesis: an alternative pathway for the regulation of inflammation.

Regulation of inflammation is a crucial event since its alteration, such as in sepsis and chronic autoimmune (i.e. rheumatoid arthritis, lupus erythematosus) or infectious diseases (i.e. tuberculosis, leprosy), determines severe tissue damage. Although there is a general consensus that regulation of inflammation results from a balance between proinflammatory and antiinflammatory pathways, we arrived at the conclusion that well known chemoattractants/proinflammatory molecules such as bacterial formyl peptides or immune complexes (IC), could induce, paradoxically, strong antiinflammatory effects. Thus, we demonstrated that N-formyl-methionyl-leucyl-phenylalanine (FMLP) exerted a drastic antiinflammatory effect, inhibiting the secretion of tumor necrosis alpha (TNF-alpha) induced by lipopolysaccharides, a potent TNF-alpha inducer. We also determined that in human neutrophils FMLP and IC induced the downregulation of receptors for the Fc portion of IgG (FcgammaRII and FcgammaRIIIB). Moreover, FMLP inhibited interferon gamma (IFN-gamma)-induced FcgammaRI expression and IC downregulate class II molecules of the major histocompatibility complex on monocytes. Part of these effects were mediated by the release of aspartic-, serin-, or metalloproteases. All these results favor the postulation of a new concept on the regulation of inflammation carried out through an alternative and non conventional pathway, in which a chemoattractant/proinflammatory agent could, under certain circumstances, act as an antiinflammatory molecule.

Hypotesis: an alternative pathway for the regulation of inflammation

Hipótesis: una vía alternativa de regulación de procesos inflamatorios. La regulación de mecanismos inflamatorios es un evento crucial debido a que una alteración de los mismos, como sucede por ejemplo, en la sepsis, en enfermedades autoinmunes crónicas (artritis reumatoidea, lupus eritematoso) o en enfermedades infecciosas (tuberculosis, lepra), genera daños tisulares severos. Aunque hay un consenso general de que la regulación de procesos inflamatorios resulta de un balance entre vías proinflamatorias y antiinflamatorias, nosotros arribamos a la conclusión de que moléculas quimioatractantes / proinflamatorias como, por ejemplo, péptidos formilados bacterianos o complejos inmunes (CI), pueden también inducir, paradójicamente, potentes efectos ntiinflamatorios. Así, demostramos que el péptido formilado prototipo N-formilmetionil- leucil-fenilalanina (FMLP), ejerce un drástico efecto antiinflamatorio, inhibiendo la secreción de factor de necrosis tumoral alfa (TNF-α) inducido por lipopolisacáridos, un potente inductor de la secreción de TNF-α. También determinamos que el FMLP y los CI inducen la disminución de la expresión de receptores para el fragmento Fc de IgG (FcγRII and FcγRIIIB) en neutrófilos humanos. Más aún, el FMLP inhibe la inducción de la expresión de los FcγRI por interferón gamma (IFN-γ) y los CI disminuyen la expresión de moléculas de clase II del complejo mayor de histocompatibilidad en monocitos humanos. Parte de esos efectos fueron mediados por la liberación de aspártico-, serino-, o metaloproteasas. Todos estos resultados nos permiten especular sobre un nuevo concepto en el cual la regulación de los procesos inflamatorios también puede llevarse a cabo por una vía alternativa, no convencional, en la cual un agente quimioatractante / proinflamatorio, bajo determinadas circunstancias, puede actuar como una molécula antiinflamatoria.(AU)

Lysis of autologous macrophages pulsed with hsp10 from Mycobacterium leprae is associated to the absence of bacilli in leprosy.

Peripheral blood mononuclear cells from leprosy patients and normal individuals were analysed for their ability to lyse autologous macrophages pulsed with the Mycobacterium leprae 10 kDa heat shock protein (hsp10), an antigen considered to have an important role in the protective responses in leprosy. Strong cytotoxic responses, with an involvement of gammadelta T and class-I and class-II restricted alphabeta T cells and/or CD16+56+ cells, were observed in normal individuals, paucibacillary (PB) and those multibacillary (MB) patients with undetectable bacillary load. On the contrary, only a weak class-II restricted cytotoxic response was observed in those MB patients with positive bacillary load (MB(+)). Simultaneous addition of IFNgamma plus TNFalpha and IL-12 during hsp10 stimulation could partially upregulate the low cytotoxic response observed in MB(+) by enhancing class-II restricted T cell activity and by development of gammadelta T and/or CD16+56+ cell activity. Our results suggest that the ability to mount an effective cytotoxic response against hsp10-pulsed macrophages in leprosy patients is closely related to the patient's bacterial load and not to the clinical form of the disease.

Interleukin-12 amplifies the M. leprae hsp65-cytotoxic response in the presence of tumour necrosis factor-alpha and interferon-gamma generating CD56+ effector cells: interleukin-4 downregulates this effect.

Interleukin-12 (IL-12) is a major immunomodulatory cytokine that represents a functional bridge between the early resistance and the subsequent antigen specific adaptive immunity. TNF-alpha and IFN-gamma have an important role in the generation of hsp65 specific cytotoxic T lymphocytes (CTL) that lyse hsp65-pulsed autologous macrophages (hsp65 CTL). Since a positive feedback mechanism between TNF-alpha, IFN-gamma and IL-12 has been described, we undertook to evaluate the role of IL-12 on the hsp65 CTL generation in leprosy patients. Our results show that the presence of IL-12 during the first 24 h of the in vitro antigen stimulation amplifies the hsp65 cytotoxic response whenever both IFN-gamma and TNF-alpha are present. The addition of these three cytokines (CKs) was able to abrogate the inhibitory effect of IL-10 on hsp65 CTL in cells from paucibacillary patients (PB) but not that of IL-4 in PB and normal controls (N). Both IL-12 or anti IL-4 enhanced the cytotoxic activity in cells from multibacillary patients (MB). Anti IL-4 upregulated the binding of IFN-gamma and did not modify that of TNF-alpha so the low CTL activity could be as a result of IL-4 by a decrease of the IFN-gamma binding on MB cells. Cells from those MB patients taking thalidomide (MB-T) did neither bind IFN-gamma nor TNF-alpha even when antigen or anti-IL-4 were added, demonstrating that thalidomide inhibits either the in vitro binding or receptor expression of both TNF-alpha and IFN-gamma. Development of CD56 effector cells during the hsp65 stimulation was observed in PB and N by the addition of IL-12 plus TNF-alpha and IFN-gamma, while in MB and MB-T anti IL-4 was also required. So, the inhibitory effect of IL-4 on either production of IFN-gamma, TNF-alpha and/or IL-12 or their receptors could be the mechanism underlying the lack of the hsp65 CTL generation in cells from MB.

Inherited variability of tumor necrosis factor production and susceptibility to infectious disease.

Tumor necrosis factor (TNF) is a critical mediator of host defense against infection but may cause severe pathology when produced in excess. Individuals vary in the amount of TNF produced when their peripheral blood mononuclear cells are stimulated in vitro, and family studies indicate that much of this variability is genetically determined. Since the TNF response to infection is partly regulated at the transcriptional level, TNF promoter polymorphisms have been the subject of intense interest as potential determinants of disease susceptibility. A single nucleotide polymorphism at nucleotide -308 relative to the transcriptional start site has been associated with susceptibility to severe malaria, leishmaniasis, scarring trachoma, and lepromatous leprosy. Some experimental data indicate that this polymorphism acts to upregulate TNF transcription, but this remains controversial. Detailed analysis of multiple genetic markers at this locus and more sophisticated investigations of TNF transcriptional regulation, in different cell types and with a wide range of stimuli, are required to understand the molecular basis of these disease associations.

Roles of tumor necrosis factor-alpha and transforming growth factor-beta in regulating intercellular adhesion molecule-1 expression on murine peritoneal macrophages infected with M. leprae.

Profiles of intercellular adhesion molecule-1 (ICAM-1) expression on murine peritoneal macrophages (M phi s) infected with Mycobacterium leprae during cultivation were examined with special reference to the regulatory effects of tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta). When M phi s were infected with M. leprae or stimulated with heat-killed M. leprae at day 0, their ICAM-1 expression, measured in terms of the ratio of M phi s positively stained with anti-ICAM-1 antibody (Ab), rapidly increased, peaking during days 1 to 3 and thereafter fell, returning to the normal level by day 7. The addition of TNF-alpha or anti-TGF-beta Ab inhibited the middle phase (day 7) downregulation of M phi ICAM-1 expression, although the late-phase (day 14) downregulation of ICAM-1 was not prevented by them. M. leprae-infected M phi s released small amounts of TNF-alpha and significant amounts of TGF-beta into the culture medium. This may indicate that M. leprae-infected M phi s produced the majority of TNF-alpha in a membrane-bound form. Alternatively, endogenous TNF-alpha might upregulate M phi ICAM-1 expression even at very low concentrations. In any case, these findings indicate the central roles of TNF-alpha and TGF-beta in the early phase upregulation and the middle-to-late phase downregulation, respectively, of ICAM-1 expression by M. leprae-infected M phi s.

Spontaneous apoptosis in peripheral blood mononuclear cells of leprosy patients: role of cytokines.

Peripheral blood mononuclear cells from leprosy patients underwent spontaneous apoptosis upon culture for 24 h. The apoptosis was inhibited by anti-TNFalpha antibodies and to a certain extent by anti-IL-1alpha and IL-6, thus showing that T(H)2-type cytokines (mainly TNFalpha) are responsible for inducing apoptosis. This cytokine-mediated apoptosis could be inhibited by ionomycin and zinc, thereby suggesting that these metal ions can be used to decrease the levels of these inflammatory cytokines in various diseases.

Roles of tumor necrosis factor-alpha and transforming growth factor-beta in regulating intercellular adhesion molecule-1 expression on murine peritoneal macrophages infected with M. Leprae

Profiles of intercellular adhesion molecule-1 (ICAM-1) expression on murine peritoneal macrophages (M phi s) infected with Mycobacterium leprae during cultivation were examined with special reference to the regulatory effects of tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta). When M phi s were infected with M. leprae or stimulated with heat-killed M. leprae at day 0, their ICAM-1 expression, measured in terms of the ratio of M phi s positively stained with anti-ICAM-1 antibody (Ab), rapidly increased, peaking during days 1 to 3 and thereafter fell, returning to the normal level by day 7. The addition of TNF-alpha or anti-TGF-beta Ab inhibited the middle phase (day 7) downregulation of M phi ICAM-1 expression, although the late-phase (day 14) downregulation of ICAM-1 was not prevented by them. M. leprae-infected M phi s released small amounts of TNF-alpha and significant amounts of TGF-beta into the culture medium. This may indicate that M. leprae-infected M phi s produced the majority of TNF-alpha in a membrane-bound form. Alternatively, endogenous TNF-alpha might upregulate M phi ICAM-1 expression even at very low concentrations. In any case, these findings indicate the central roles of TNF-alpha and TGF-beta in the early phase upregulation and the middle-to-late phase downregulation, respectively, of ICAM-1 expression by M. leprae-infected M phi s.

[The expression of ICAM-1 on macrophages stimulated with Mycobacterium avium complex and its control by some regulatory cytokines].

The interaction of LFA-1 on T lymphocytes with ICAM-1 on antigen presenting cells (APCs) is critical in determining conjugate formation between the APCs and T cells as well as activation of T cells. Recently, it was found that stimulation of THP-1 cells, a human monocyte M phi cell line, with Mycobacterium tuberculosis or its lipoarabinomannan, elicited the increase in the ICAM-1 expression. In addition, in cases of lepromatous leprosy patients with a serious defect in the M. leprae antigen-specific cellular immunity, keratinocytes in the leprosy lesions were lacking in the ICAM-1 expression. Therefore, ICAM-1 seems to participate in the host response to mycobacterial infections. Here, we studied the mode of the expression of ICAM-1 molecules on murine peritoneal M phis in response to stimulation with M. avium complex (MAC). In addition, the regulatory effect of some cytokines including TNF-alpha, IL-10, and transforming growth factor-beta (TGF-beta) on the ICAM-1 expression was studied. Monolayer cultures of peptone-starch induced murine peritoneal M phis were cultured in RPMI-1640 medium in the presence of MAC with or without test agents. At intervals, the M phis were stained with anti-ICAM-1 antibody (Ab) and then treated with alkaline phosphatase (Ap)-conjugated anti-1g Ab. After color development with NBT-BCIP substrate, percentage of the blue-stained (ICAM-1 positive) M phis was determined microscopically. The concentrations of TNF-alpha, IL-10, and TGF-beta in the M phi culture fluid was measured by ELISA using capture Ab, biotin-labelled capping Ab, and Ap-conjugated streptavidin. When M phis infected with MAC organisms were cultured in RPMI medium containing 10% fetal bovine serum or in serum-free GPI medium, a significant increase in their ICAM-1 expression was observed, reaching the peak at days 1 to 3, thereafter rapidly decreased and returned to the normal level by day 14. Further addition of TNF-alpha caused no significant change in the mode of the MAC-induced expression of ICAM-1. A transient increase in the IL-10 production of MAC-infected M phis was observed during the first 3-days cultivation, as in the case of TNF-alpha. On the other hand, TGF-beta production of the Mø population was initiated from day 3, and therafter increased gradually until day 14. ICAM-1 expression of the MAC-infected M phis was not influenced by the addition of IL-10, while anti-IL-10 Ab retarded the decline of ICAM-1 expression at day 7. On the other hand, the addition of TCF-beta attenuated the MAC infection-induced increase in the ICAM-1 expression significantly. In addition, anti-TGF-beta Ab significantly delayed the reduction of the ICAM-1 expression of MAC-infected M phis during days 3 to 7. These results indicate that, in the MAC-infected M phis. TGF-beta rather than IL-10 play important roles as a mediators for the late-phase down-regulation of ICAM-1 expression which had been transiently elevated by the action of TNF-alpha in the early phase of the Mø cultivation.

Tumour necrosis factor-alpha (TNF-alpha) synthesis is associated with the skin and peripheral nerve pathology of leprosy reversal reactions.

Leprosy may be complicated by episodes of increased cell-mediated immunity towards Mycobacterium leprae (reversal reactions) which result in severe local immunopathology in skin lesions and peripheral nerves. Using in situ hybridization and MoAb techniques we have demonstrated TNF-alpha mRNA and TNF-alpha protein in macrophages infiltrating leprosy skin and peripheral nerve. Levels of TNF-alpha mRNA are significantly increased in reactional skin and nerve, particularly in borderline tuberculoid patients. TNF-alpha mRNA and TNF-alpha protein levels are higher in reactional nerves then reactional skin. In both reactional skin and nerve TNF-alpha mRNA is more abundant than TNF-alpha protein; this may reflect the rapid turnover of TNF-alpha protein in an immunologically dynamic situation, such as is seen in reversal reaction. Our findings emphasize the importance of documenting both mRNA and protein production when assessing the role of cytokines in pathology. The leprosy reversal reaction may be regarded as a useful model of tissue immunopathology in which TNF-alpha is generated as part of the host response to infection, but also produces local tissue damage.

Nerve lesions induced by macrophage activation.

The neuropathies associated with infectious processes, including leprosy, retroviral infections and Chagas' disease, represent the largest group of neuropathies in the world. Segmental demyelination and axonal degeneration of nerve fibres are associated with inflammatory infiltrates which contain a large number of mononuclear phagocytes. In order to learn more about the role played by macrophage activation in the nerve lesions observed in inflammatory neuropathies, we have performed a morphological study of nerves injected with products of activation of macrophages including proteolytic enzymes and cytokines (tumour necrosis factor and alpha beta-interferon). We have also studied the effects on nerve fibres of macrophages activated by ingestion of proteose-peptone, a foreign protein, and in the course of a delayed-type hypersensitivity (DTH) reaction. We have found that proteases and urokinase were potent demyelinating agents and that activated macrophages were also able to induce significant demyelination of neighbouring fibres. In contrast, injection of TNF alpha induced more severe nerve lesions consisting of axonal degeneration of the majority of nerve fibres. We thus conclude that infected macrophages which penetrate the endoneurium and macrophages activated in a DTH reaction can both cause neuropathy.

The role of monokines in granuloma formation in mice: the ability of interleukin 1 and tumor necrosis factor-alpha to induce lung granulomas.

Granulomatous inflammation is associated with many significant human diseases, including tuberculosis, leprosy, sarcoidosis, parasite infection, and berylliosis. Very little is known about the basic mechanism of this type of inflammation. In the present study, we showed that pulmonary granulomas were induced in mice by the intratracheal injection of agarose beads coupled to recombinant interleukin 1 (IL-1) or tumor necrosis factor-alpha (TNF-alpha). Histologically, the bulk of granulomas was composed of macrophages and their derivatives. In contrast, the inflammatory reactions induced by beads coupled to either recombinant IL-2 or murine interferon-gamma were considerably smaller than those induced by beads coupled to monokines. These results suggest that macrophages and monokines such as IL-1 and TNF-alpha, but not T cell-derived lymphokines, play an essential role in granuloma formation.