A fraction of tubercle bacilli possessing primary toxicity

Cord factor as an invisibility cloak? A hypothesis for asymptomatic TB persistence

Mycobacterium tuberculosis (MTB) has long been known to persist in grossly normal tissues even in people with active lesions and granulomas in other parts of the body. We recently reported that post-primary TB begins as an asymptomatic infection that slowly progresses, accumulating materials for a massive necrotizing reaction that results in cavitation. This paper explores the possible roles of trehalose 6,6' dimycolate (TDM) or cord factor in the ability of MTB to persist in such lesions without producing inflammation. TDM is unique in that it has three distinct sets of biologic activities depending on its physical conformation. As a single molecule, TDM stimulates macrophage C-type lectin receptors including Mincle. TDM can also form three crystal like structures, cylindrical micelles, intercalated bilayer and monolayer, that have distinct non receptor driven activities that depend on modulation of interactions with water. In the monolayer form, TDM is highly toxic and destroys cells in minutes upon contact. The cylindrical micelles and an intercalated bilayer have surfaces composed entirely of trehalose which protect MTB from killing in macrophages. Here we review evidence that these trehalose surfaces bind water. We speculate that this immobilized water constituites of an "invisibility cloak" that facilitates the persistence of MTB in multiple cell types without producing inflammation, even in highly immune individuals.

TB research at UT-Houston--a review of cord factor: new approaches to drugs, vaccines and the pathogenesis of tuberculosis

Tuberculosis remains a major threat as drug resistance continues to increase. Pulmonary tuberculosis in adults is responsible for 80% of clinical cases and nearly 100% of transmission of infection. Unfortunately, since we have no animal models of adult type pulmonary tuberculosis, the most important type of disease remains largely out of reach of modern science and many fundamental questions remain unanswered. This paper reviews research dating back to the 1950's providing compelling evidence that cord factor (trehalose 6,6 dimycolate [TDM]) is essential for understanding tuberculosis. However, the original papers by Bloch and Noll were too far ahead of their time to have immediate impact. We can now recognize that the physical and biologic properties of cord factor are unprecedented in science, especially its ability to switch between two sets of biologic activities with changes in conformation. While TDM remains on organisms, it protects them from killing within macrophages, reduces antibiotic effectiveness and inhibits the stimulation of protective immune responses. If it comes off organisms and associates with lipid, TDM becomes a driver of tissue damage and necrosis. Studies emanating from cord factor research have produced (1) a rationale for improving vaccines, (2) an approach to new drugs that overcome natural resistance to antibiotics, (3) models of caseating granulomas that reproduce multiple manifestations of human tuberculosis. (4) evidence that TDM is a key T cell antigen in destructive lesions of tuberculosis, and (5) a new understanding of the pathology and pathogenesis of postprimary tuberculosis that can guide more informative studies of long standing mysteries of tuberculosis.

The influence of thymic and bursal lymphoid systems in avian tuberculosis

Intact and immunologically deficient chickens inoculated with M avium were examined for structural changes in the spleen, the tuberculin reactions and antibody formation. Intravenous inoculation caused miliary tuberculosis of spleen and liver but not brain; intracerebral inoculation caused massive lymphocytic tuberculosis meningitis with later spread to spleen and liver. Neonatal bursectomy and thymectomy did not significantly alter the disease in terms of survival and lesion structure. Cortisone induced earlier development of lesions.In spleen, bacilli were first seen 5 days after inoculation in macrophages in the lymphoid sheath-particularly in capsules of germinal centers. Subsequent lesions were tubercles in the lymphoid sheath, hyperplasia of penicillar arteriolar sheaths, lymphoid atrophy and amyloid deposition. Tubercles were composed of infected macrophages located centrally and surrounded by lighter noninfected macrophages. Cell membranes were extensively interwined where these cells were in contact. Mycobacteria were present within dense, membrane-bound residual bodies.Antibody was first detected 8 days after inoculation in intact birds and persisted throughout the disease. Tuberculin reactions were mixtures of a perivascular monocytic response (delayed hypersensitivity) which developed early and was absent terminally, and a vasculonecrotic response which developed later and persisted to death of the bird. Both reactions occurred in the absence of detectable antibody in bursectomized birds.

Some biological properties of BCG after the extraction of lipids: the power to irritate tissues, the ability to prepare for and to evoke Bail's phenomenon, and the power to sensitize to tuberculin

Mycobacterium tuberculosis var. bovis BCG was treated with lipid solvents according to Macheboeuf's method and five progressively more fully extracted bacillary residues were obtained. Electron-microscope examination, together with the biological properties studied, showed that a major transformation was brought about in the bacillary residues by methanol extraction. The biological properties of the residues were studied quantitatively in guinea pigs. The power to irritate tissues (i.e., to produce tuberculous-like lesions in tissues), the ability to prepare for and to evoke Bail's phenomenon (i.e., reaction to the intraperitoneal introduction of bacillary bodies in a sensitized guinea pig characterized by an immediate leucocytic response and death within a few hours), and the power to sensitize to tuberculin were directly proportional to the lipid contents of the bacillary bodies and decreased as the extraction progressed. The residues with the lower lipid contents were less irritant, less sensitizing, and less reactive. However, these properties never completely disappeared. The role of the lipids as related to the above properties of mycobacteria was thus indirectly established. With the doses and the routes of injection used, no obvious toxic effects in normal guinea pig were observed.

Studies on tubercle bacillus-monocyte relationship. II. Induction of monocyte degeneration by bacteria and culture filtrate: specificity of serum and monocyte effects on resistance to degeneration

Studies of virulent, attenuated, and avirulent strains of tubercle bacilli have demonstrated the proficiency of virulent strains to effect degeneration of normal monocytes cultivated in the presence of normal serum. Attenuated strains were less active in this respect, and avirulent bacilli failed to induce monocytic degeneration. Comparison of the effects of virulent H37Rv with O.T., P.P.D., and a culture filtrate of H37Rv revealed a similarity in action of H37Rv and its filtrate. The action of O.T. and P.P.D. differed from that of H37Rv in that the greatest effect of H37Rv was upon normal cells as opposed to the effect of O.T. and P.P.D. upon immune cells. Additionally, it was demonstrated that immune serum (anti-BCG) protected immune cells against H37Rv but not against O.T. or P.P.D. The protection of immune cells by heterologous antisera (anti-Salmonella and anti-ovalbumin) as well as by homologous antiserum (anti-BCG) against the degenerative effects of H37Rv indicated a non-specificity in action of serum factors. The ability of the monocytes of animals immunized with BCG and the failure of monocytes of animals immunized with Salmonella rutgers to withstand parasitization with H37Rv, when both types of monocytes were cultivated in immune (anti-BCG) serum, indicated a specificity of cellular resistance.

Antituberculous immunity induced by methanol extracts of tubercle bacilli; its enhancement by adjuvants

It is possible to prepare from tubercle bacilli a fraction soluble in methanol which is capable of eliciting in mice a marked degree of resistance against virulent tuberculous infection. The immunity was evident whether the infective dose was large and caused a disease with a rapid course, or was very small and caused a disease of many months duration. Active material has been obtained by extraction with methanol at 55 degrees C. of bacterial cells killed with 2 per cent phenol, and washed with acetone. The methanol extracts used in the present study have been prepared from the phenol-killed cells of a culture of BCG, and of the avirulent culture H37Ra. Vaccination of mice bas been carried out by the intraperitoneal route, and the challenge infection (with a highly virulent bovine culture), by the intravenous route. Weight for weight, the protective activity of the methanol extract is smaller than that of the bacterial cells from which it is extracted, but its primary toxicity for mice is also considerably lower. The protective activity can be increased, and the immunity prolonged, by using certain adjuvants as vehicle for injection of the vaccine. An oil adjuvant mixture, and small amounts of a highly purified preparation of the somatic antigen of typhoid bacilli, have been found capable of enhancing and prolonging the antituberculous immunity induced by the methanol extract. Under appropriate conditions the resistance resulting from intraperitoneal injection of the methanol extract is of the same order as that which follows vaccination with whole killed tubercle bacilli or with living BCG.

Antituberculous immunity induced in mice by vaccination with killed tubercle bacilli or with a soluble bacillary extract

It proved possible to increase the resistance of mice to tuberculous infection by vaccinating them with a suspension of avirulent tubercle bacilli killed by exposure to 2 per cent phenol. This increase in resistance was demonstrated by two different techniques: (a) observation of survival time of vaccinated animals following challenge infection with a large dose of virulent bacilli, and (b) determination of numbers of virulent bacilli in the spleens of animals 2 weeks after injection of a small infective dose. The minimum protective dose of vaccine corresponded to approximately one-tenth the acutely toxic dose. Addition of an adjuvant to the bacillary suspension markedly increased both the protective effectiveness of the vaccine and the duration of the immunity. It enhanced also the toxicity of the vaccine in approximately the same proportion. However, other lines of evidence suggested that toxicity and protective activity were independent one from the other and were the manifestations of different bacillary constituents. Extraction with absolute methanol released from the bacillary bodies a crude soluble fraction possessing low, if any, toxicity, yet capable of eliciting in mice a state of increased resistance to virulent infection. The protective activity of this methanol-soluble fraction was low; it accounted for only a small part of the total protective activity of the original material.