Cell-mediated immune response against mycolic acids of Mycobacteroides salmoniphilum in rainbow trout Oncorhynchus mykiss

Mycobacteriosis caused by Mycobacterium spp. causes economic damages to the world aquaculture industry. In mammals, mycolic acids contained in the cell wall of Mycobacterium spp. are presented by CD1b molecule as lipid antigens and induce cell-mediated immunity (CMI). Here, we investigated CMI responses against the mycolic acids of Mycobacterioides salmoniphilum in a CD1-lacking teleost fish, rainbow trout. After stimulation of trout leukocytes with mycolic acids, the number and percentage of CD8α⁺ T cells increased. Fish immunized with mycolic acids showed an up-regulation of IFN-γ. Further, in vitro re-stimulation of leukocytes derived from immunized fish resulted in proliferation of CD8α⁺ cells. These data suggest that mycolic acids are recognized as lipid antigens resulting in an activation of rainbow trout CD8α⁺ cells and up-regulation of the Th1 cytokine IFN-γ. The mycolic acids are promising candidates for vaccines to activate CD8α⁺ T cells against fish mycobacteriosis.

The antigenicity and cholesteroid nature of mycolic acids determined by recombinant chicken antibodies

Mycolic acids (MA) are major, species-specific lipid components of Mycobacteria and related genera. In Mycobacterium tuberculosis, it is made up of alpha-, methoxy- and keto-MA, each with specific biological functions and conformational characteristics. Antibodies in tuberculosis (TB) patient sera respond differently towards the three MA classes and were reported to cross-react with cholesterol. To understand the antigenicity and cholesterol cross-reactivity of MA, we generated three different chicken -derived phage-displayed single-chain variable fragments (scFv) that reacted similarly towards the natural mixture of MA, but the first recognized all three classes of chemically synthetic MAs, the second only the two oxygenated types of MAs and the third only methoxy MA. The cholesterol cross-reactivity was investigated after grafting each of the three scFv types onto two configurations of constant chain domains–CH1-4 and CH2-4. Weak but significant cross-reactivity with cholesterol was found only with CH2-4 versions, notably those two that were also able to recognize the trans-keto MA. The cholesteroid nature of mycobacterial mycolic acids therefore seems to be determined by the trans-keto MA subclass. The significantly weaker binding to cholesterol in comparison to MA confirms the potential TB diagnostic application of these antibodies.

CD1b-restricted GEM T cell responses are modulated by Mycobacterium tuberculosis mycolic acid meromycolate chains

Tuberculosis (TB), caused by Mycobacterium tuberculosis, remains a major human pandemic. Germline-encoded mycolyl lipid-reactive (GEM) T cells are donor-unrestricted and recognize CD1b-presented mycobacterial mycolates. However, the molecular requirements governing mycolate antigenicity for the GEM T cell receptor (TCR) remain poorly understood. Here, we demonstrate CD1b expression in TB granulomas and reveal a central role for meromycolate chains in influencing GEM-TCR activity. Meromycolate fine structure influences T cell responses in TB-exposed individuals, and meromycolate alterations modulate functional responses by GEM-TCRs. Computational simulations suggest that meromycolate chain dynamics regulate mycolate head group movement, thereby modulating GEM-TCR activity. Our findings have significant implications for the design of future vaccines that target GEM T cells.

Structure-function relationships of the antigenicity of mycolic acids in tuberculosis patients

Cell wall mycolic acids (MA) from Mycobacterium tuberculosis (M.tb) are CD1b presented antigens that can be used to detect antibodies as surrogate markers of active TB, even in HIV coinfected patients. The use of the complex mixtures of natural MA is complicated by an apparent antibody cross-reactivity with cholesterol. Here firstly we report three recombinant monoclonal scFv antibody fragments in the chicken germ-line antibody repertoire, which demonstrate the possibilities for cross-reactivity: the first recognized both cholesterol and mycolic acids, the second mycolic acids but not cholesterol, and the third cholesterol but not mycolic acids. Secondly, MA structure is experimentally interrogated to try to understand the cross-reactivity. Unique synthetic mycolic acids representative of the three main functional classes show varying antigenicity against human TB patient sera, depending on the functional groups present and on their stereochemistry. Oxygenated (methoxy- and keto-) mycolic acid was found to be more antigenic than alpha-mycolic acids. Synthetic methoxy-mycolic acids were the most antigenic, one containing a trans-cyclopropane apparently being somewhat more antigenic than the natural mixture. Trans-cyclopropane-containing keto- and hydroxy-mycolic acids were also found to be the most antigenic among each of these classes. However, none of the individual synthetic mycolic acids significantly and reproducibly distinguished the pooled serum of TB positive patients from that of TB negative patients better than the natural mixture of MA. This argues against the potential to improve the specificity of serodiagnosis of TB with a defined single synthetic mycolic acid antigen from this set, although sensitivity may be facilitated by using a synthetic methoxy-mycolic acid.

Trans-cyclopropanation of mycolic acids on trehalose dimycolate suppresses Mycobacterium tuberculosis -induced inflammation and virulence

Recent studies have shown that fine structural modifications of Mycobacterium tuberculosis cell envelope lipids mediate host cell immune activation during infection. One such alteration in lipid structure is cis-cyclopropane modification of the mycolic acids on trehalose dimycolate (TDM) mediated by proximal cyclopropane synthase of alpha mycolates (pcaA), a proinflammatory lipid modification during early infection. Here we examine the pathogenetic role and immunomodulatory function of mycolic acid cyclopropane stereochemistry by characterizing an M. tuberculosis cyclopropane-mycolic acid synthase 2 (cmaA2) null mutant (Delta cmaA2) that lacks trans-cyclopropanation of mycolic acids. Although titers of WT and Delta cmaA2 organisms were identical during mouse infection, Delta cmaA2 bacteria were hypervirulent while inducing larger granulomas than WT M. tuberculosis. The hypervirulence of the Delta cmaA2 strain depended on host TNF-alpha and IFN-gamma. Loss of trans-cyclopropanation enhanced M. tuberculosis-induced macrophage inflammatory responses, a phenotype that was transferable with petroleum ether extractable lipids. Finally, purified TDM lacking trans-cyclopropane rings was 5-fold more potent in stimulating macrophages. These results establish cmaA2-dependent trans-cyclopropanation of TDM as a suppressor of M. tuberculosis-induced inflammation and virulence. In addition, cyclopropane stereochemistries on mycolic acids interact directly with host cells to both positively and negatively influence host innate immune activation.

Of mice, men, and elephants: Mycobacterium tuberculosis cell envelope lipids and pathogenesis

Mycolic acids and structures attached to them constitute a major part of the protective envelope of Mycobacterium tuberculosis, and for this reason, their role in tuberculosis pathogenesis has been extensively studied. In this issue of the JCI, Rao et al. examine the effect of trans-cyclopropanation of oxygenated mycolic acids attached to trehalose dimycolate (TDM) on the murine immune response to infection (see the related article beginning on page 1660). Surprisingly, they found that an M. tuberculosis mutant lacking trans-cyclopropane rings was hypervirulent in mice. The recent recognition of a hypervirulence phenotype in mice associated with laboratory and clinical M. tuberculosis strains with altered cell wall components has provided new insights into how M. tuberculosis may establish persistent infection. However, to date, characterization of these bioactive products in pathogenesis has been largely reductionistic; the relationship of their effects observed in mice to the persistent infection and tuberculosis caused by M. tuberculosis observed in humans remains obscure.

The Mycobacterium tuberculosis cell wall component mycolic acid elicits pathogen-associated host innate immune responses

Recognition of conserved pathogen-associated molecular patterns constitutes a crucial step in the initiation of innate immune responses. We studied the contribution to the host-pathogen interaction of mycolic acid (MA), a major lipid component of the cell envelope of the macrophage intracellular pathogen Mycobacterium tuberculosis and other mycobacteria. MA administered to the peritoneal cavity or to the airways induced a unique macrophage morphotype, similar to the foamy macrophage derivatives observed in tuberculous granulomas and characterized by intracellular accumulation of neutral lipids and entry into mitosis. When assayed for production of inflammatory mediators, a conditioning rather than a direct activation of the MA-elicited foamy macrophages was observed. MA enabled production of IFN-gamma and myeloperoxidase, enhanced TNF-alpha production and suppressed IL-10 upon renewed exposure to innate triggers. Intratracheal instillation of MA mimicked additional features of the airway response to M. tuberculosis infection, namely a rapid but transient neutrophil influx and IL-6 production and a chronic IL-12 production. These MA-elicited cellular innate defenses and the accompanying formation of foamy macrophages identify for the first time the foamy macrophage morphotype as part of the host response to a pathogen-associated structure. Furthermore, these results characterize MA as a direct trigger of innate immunity, distinct from Toll-like receptor ligands.

Understanding the function of CD1-restricted T cells

CD1 molecules bind foreign lipid antigens as they survey the endosomal compartments of infected antigen-presenting cells. Unlike T cells that recognize CD1-restricted foreign lipids, CD1-restricted T cells that are self-antigen-reactive function as 'auto-effectors' that are rapidly stimulated to carry out helper and effector functions upon interaction with CD1-expressing antigen-presenting cells. The functional distinctions between subsets of CD1-restricted T cells, and the pathways by which these cells both influence the inflammatory and tolerogenic effects of dendritic cells and activate natural killer cells and other lymphocytes, provide insight into how CD1-restricted T cells regulate antimicrobial responses, antitumor immunity and the balance between tolerance and autoimmunity.

Immunomagnetic separation of scum-forming bacteria using polyclonal antibody that recognizes mycolic acids

Mycolic acid-containing bacteria (mycolata) are thought to be involved in scum formation in aeration basins of activated sludge plants due to their ability to produce biosurfactants and their cell surface hydrophobicity. To isolate these bacteria, immunomagnetic separation (IMS) using an anti-mycolic acid polyclonal antibody was investigated. IMS that targeted Gordonia amarae SC1 exhibited a 100% recovery at 5x10(3) CFU ml(-1). At cell concentration of 7.8x10(6) CFU ml(-1), the recovery was lowered, but 80% of cells were still captured. Effect of bead concentrations on the recovery of SC1 at 10(6) CFU ml(-1) was examined. The results showed that addition of more than 6-7x10(6) beads for 1x10(6) CFU reached a maximum recovery (83%). Furthermore, the IMS procedure optimized with SC1 cells was tested with another mycolata. The results suggested that variation of the recovery for each mycolata is dependent on the specificity of the polyclonal antibody and that mycolata which are recognized by the antibody can be recovered by this procedure.

Prevalence of anti-mycolic acid antibodies in patients with pulmonary tuberculosis co-infected with HIV

Isolation and purification of mycolic acids from Mycobacterium tuberculosis have allowed them to be applied as antigen in an ELISA-based assay to detect specific antibodies in human sera. Tuberculosis patients have previously been shown to contain antimycolic acids antibodies. The aim of this study was to determine whether human immunodeficiency virus (HIV) co-infection increases false-negative testing rate and whether other random diseases for which hospitalisation is normally required will contribute to false-positive results. Sera from 118 human subjects were tested for the presence of antibodies to mycolic acids; 59 were patients with proven pulmonary tuberculosis and 59 were control hospitalised patients without evidence of tuberculosis. Each group consisted of HIV-seropositive and HIV-seronegative subjects. The endpoint was the detection of specific antibodies to mycolic acids in the sera, before and after precipitation of immune complexes. The two groups of subjects were well matched for age, gender, race and HIV status. On average, humans infected with Mycobacterium tuberculosis showed a specific antibody response to mycolic acids that was not affected by low CD4 T-lymphocyte counts in HIV-seropositive patients but was compromised by various other serious diseases.

Mycolic acids from Mycobacterium tuberculosis: purification by countercurrent distribution and T-cell stimulation

Bacterial cell wall lipids are recognized as immunostimulatory molecules which make an important component of vaccines against bacterial diseases. Even mycolic acids, forming the waxy outer layer of the bacilli which cause tuberculosis, have been shown to stimulate human CD4/8 double negative T-cells. The role of these cells in resistance to tuberculosis is currently still debated. In this work, a method is described to purify mycolic acids from bacterial crude extracts in a single step using countercurrent distribution. Mycolic acids obtained in this way approach 100% purity and stimulate both double negative and CD4 positive T-cells in peripheral blood leucocytes obtained from healthy human donors. Stimulation of CD4 cells by mycolic acid antigens has not been reported before, emphasizing the potential importance of mycolic acids in the context of the fight against tuberculosis.

Fine specificity of TCR complementarity-determining region residues and lipid antigen hydrophilic moieties in the recognition of a CD1-lipid complex

alphabeta TCR can recognize peptides presented by MHC molecules or lipids and glycolipids presented by CD1 proteins. Whereas the structural basis for peptide/MHC recognition is now clearly understood, it is not known how the TCR can interact with such disparate molecules as lipids. Recently, we demonstrated that the alphabeta TCR confers specificity for both the lipid Ag and CD1 isoform restriction, indicating that the TCR is likely to recognize a lipid/CD1 complex. We hypothesized that lipids may bind to CD1 via their hydrophobic alkyl and acyl chains, exposing the hydrophilic sugar, phosphate, and other polar functions for interaction with the TCR complementarity-determining regions (CDRs). To test this model, we mutated the residues in the CDR3 region of the DN1 TCR beta-chain that were predicted to project between the CD1b alpha helices in a model of the TCR/CD1 complex. In addition, we tested the requirement for the negatively charged and polar functions of mycolic acid for Ag recognition. Our findings indicate that the CDR loops of the TCR form the Ag recognition domain of CD1-restricted TCRs and suggest that the hydrophilic domains of a lipid Ag can form a combinatorial epitope recognized by the TCR.

Evidence for human CD4+ T cells in the CD1-restricted repertoire: derivation of mycobacteria-reactive T cells from leprosy lesions

Both the CD4-CD8- (double negative) and CD4-CD8+ T cell lineages have been shown to contain T cells which recognize microbial lipid and glycolipid Ags in the context of human CD1 molecules. To determine whether T cells expressing the CD4 coreceptor could recognize Ag in the context of CD1, we derived CD4+ T cell lines from the lesions of leprosy patients. We identified three CD4+ Mycobacterium leprae-reactive, CD1-restricted T cell lines: two CD1b restricted and one CD1c restricted. These T cell lines recognize mycobacterial Ags, one of which has not been previously described for CD1-restricted T cells. The response of CD4+ CD1-restricted T cells, unlike MHC class II-restricted T cells, was not inhibited by anti-CD4 mAb, suggesting that the CD4 coreceptor does not impact positive or negative selection of CD1-restricted T cells. The CD4+ CD1-restricted T cell lines produced IFN-gamma and GM-CSF, the Th1 pattern of cytokines required for cell-mediated immunity against intracellular pathogens, but no detectable IL-4. The existence of CD4+ CD1-restricted T cells that produce a Th1 cytokine pattern suggests a contributory role in immunity to mycobacterial infection.

Anti-cord factor (trehalose 6,6'dimycolate) IgG antibody in tuberculosis patients recognizes mycolic acid subclasses

The detection of anti-cord factor (trehalose 6,6'-dimycolate) IgG antibody in active (smear-and/or culture-positive) and inactive (smear-and culture-negative) tuberculosis patients is a useful serodiagnostic tool that can be used for early clinical diagnosis of the disease. We estimated the titers of anticord factor IgG antibody in the sera of tuberculosis patients, and compared them with those of Mycobacterium avium-infected patients. Most of the serum samples obtained from the tuberculosis patients were highly reactive against M. tuberculosis (MTB) cord factor isolated from M. tuberculosis H37Rv, a human-type mycobacterial strain, whereas they were less reactive against M. avium (MAC) cord factor. Similarly, most of the serum samples of the MAC-infected patients were highly reactive against MAC cord factor and less reactive against MTB cord factor. These results suggest that anti-cord factor IgG antibody recognizes the mycolic acid subclasses as an epitope which comprises cord factor, since MTB and MAC cord factor differ in mycolic acid subclasses and molecular species composition. To clarify the exact antigenic epitope in cord factor and to find out a more sensitive and specific diagnostic test antigen, we examined the reactivity of patients' sera to glycolipids containing trehalose (cord factor and sulfolipid) obtained from various mycobacterial species. Furthermore, the reactivity of human antisera to various mycolic acid subclasses (alpha-, methoxy and keto mycolic acids) of MTB cord factor was compared. We found that anti-cord factor IgG antibody in the sera of human tuberculosis patients most strikingly recognized methoxy mycolic acid in the cord factor of M. tuberculosis, whereas it recognized alpha- and keto mycolic acids weakly. Pre-absorption studies of antibody with MTB cord factor or methoxy mycolic acid methyl ester showed that anti-cord factor antibody was absorbed partially, but consistently. This is the first report describing that the specific subclass of mycolic acid from mycobacteria is antigenic in the humoral immune system of human tuberculosis infection.

The molecular basis of CD1-mediated presentation of lipid antigens

The CD1 family of proteins mediates a newly described pathway for presentation of lipids and glycolipids for specific recognition by T cells. All four of the known human CD1 proteins (CD1a, CD1b, CD1c and CD1d) as well as murine CD1d have now been shown to mediate T-cell recognition of lipid or glycolipid antigens. These antigens include naturally occurring foreign glycolipids from intracellular pathogens or synthetic glycolipids that are related in structure to mammalian glycolipids. The CD1b and CD1d-presented antigens differ in their fine structures but reveal a general motif in which a rigid hydrophilic cap is bound to two aliphatic hydrocarbon chains. Different T-cell populations recognize individual antigens without cross-reactivity to closely related antigen structures or CD1 isoforms, documenting the complexity and fine specificity of CD1-mediated T-cell responses. Mapping of the molecular determinants of recognition for CD1b and CD1d-presented antigens reveals that T cells discriminate the fine structure of the hydrophilic cap of the antigen, but both the length and structure of the lipid chains may be altered without loss of recognition. This pattern of lipid antigen recognition may be accounted for by a simple molecular mechanism of presentation that parallels the known mechanism for presentation of peptides, but solves the special problems related to the hydrophobic chemical nature of the lipid antigens. We propose that CD1 binds antigen by accommodating the two lipid tails within the hydrophobic groove of its two membrane distal domains, positioning the rigid hydrophilic cap of the antigen on the solvent-exposed surface of the CD1 protein, where it can directly contact the T-cell antigen receptor. This model provides a molecular basis for recognition of a new and diverse set of T-cell antigens contained within the lipid bilayers of cellular membranes.

Production and partial characterization of antibody to cord factor (trehalose 6,6'-dimycolate) in mice

Antibody production against the trehalose 6,6'-dimycolate (TDM, cord factor) of Rhodococcus ruber, a non-pathogenic species of the Actinomycetales group, was investigated in mice by repeated intraperitoneal injection of TDM in water-in-oil-in-water micelles without carrier protein. The antigenic TDM was isolated and purified chromatographically from the chloroform-methanol extractable lipids of R. ruber. The hydrophobic moiety of this TDM was composed of two molecules of monoenoic or dienoic alpha-mycolic acids with a carbon chain length ranging from C44 to C48 centering at C46. To detect the antibody, an enzyme-linked immunosorbent assay (ELISA) system was employed using plastic plates coated with TDM. The antibody reacted against the TDM of R. ruber. The antibody was reactive in similar fashion against glycosyl monomycolates differing in the carbohydrate moiety, such as that of glucose mycolate (GM) and mannose mycolate (MM), obtained from R. ruber. Moreover, the antibody reacted against mycolic acid methyl ester itself when it was used as the antigen in ELISA, and trehalose did not absorb the antibody to TDM or inhibit the reaction. These results indicate that the epitope of TDM recognized by the antibody is mycolic acid, an extremely hydrophobic part of the molecule. Next, we prepared monoclonal anti-TDM antibody (moAb) in mice myeloma cells to examine its biological activities and the role of humoral immunity in mycobacterial infection. MoAb reacted against the TDM, glycosyl mycolate, and mycolic acid methyl ester in ELISA in the same manner as our polyclonal antibody did. The administration of moAb suppressed granuloma formation in the lungs, spleen, and liver induced by TDM and inhibited the production of interleukin-1 (IL-1) and chemotactic factor, which is reported to precede granuloma formation.

Production and partial characterization of anti-cord factor (trehalose-6,6'-dimycolate) IgG antibody in rabbits recognizing mycolic acid subclasses of Mycobacterium tuberculosis or Mycobacterium avium

An ELISA with cord factor (trehalose-6,6'-dimycolate) is useful for the serodiagnosis of tuberculosis. To clarify the exact antigenic epitope in cord factor, recognized by a rabbit anti-cord factor IgG antibody, and to ascertain the most sensitive and specific diagnostic test antigen, rabbits were immunized with two kinds of cord factors isolated from Mycobacterium tuberculosis or Mycobacterium avium and the reactivities of the sera were tested against cord factors or the component mycolic acid methyl esters by ELISA. The serum from rabbits immunized with M. tuberculosis cord factor was highly reactive against M. tuberculosis cord factor, but less reactive against M. avium cord factor. In contrast, the serum from rabbits immunized with M. avium cord factor was highly reactive against M. avium cord factor but less reactive against M. tuberculosis cord factor. Moreover, the serum from rabbits immunized with M. tuberculosis cord factor reacted against mycolic acid methyl esters, especially methoxy mycolic acid methyl ester. On the other hand, the serum from rabbits immunized with M. tuberculosis cord factor was less reactive against trehalose-6-monomycolate and not reactive against sulfolipid (2,3,6,6'-tetraacyl trehalose 2'-sulfate). From these results, it was concluded that the anti-cord factor IgG antibody, produced experimentally in rabbits, recognized the differences in the cord factor structures, i.e. the hydrophobic moiety rather than the carbohydrate moiety. It was also noted that the serum from rabbits immunized with M. tuberculosis cord factor was highly reactive against methoxy mycolic acid as an epitope. This paper is the first to describe how the anti-cord factor IgG antibody can recognize the mycolic acid subclasses, which differ according to the species of mycobacteria.

Uptake and processing of glycosylated mycolates for presentation to CD1b-restricted T cells

Antigen presenting cells (APCs) expressing CD1b mediate the specific T cell recognition of mycobacterial lipid antigens. These lipid antigens require internalization by APCs prior to presentation, but the detailed mechanisms of uptake and intracellular processing are not known. Here we have examined several steps in the presentation of two related classes of CD1b-presented antigens, free and glycosylated mycolates. T cell recognition of glucose monomycolate (GMM) was blocked by agents that fix APC membranes or neutralize the pH of endosomes, indicating a requirement for GMM uptake into an acidic compartment prior to recognition. Different T cell lines responded to free mycolate or GMM without crossreactivity, yet both antigens were taken up by APCs at the same rate. This demonstrated that differential recognition of these antigens resulted from T cell specificity for their hydrophilic caps and that APCs were unable to interconvert these antigens by enzymatic or chemical deglycosylation or glycosylation. APCs were also unable to cleave mycobacterial trehalose dimycolate (TDM) at its most chemically labile linkages to yield antigenic free mycolates or GMM. Our results indicate that these mycolate-containing antigens are resistant to chemical or enzymatic cleavage by APCs, suggesting that molecular trimming is not a universal feature of lipid antigen processing.

Structural requirements for glycolipid antigen recognition by CD1b-restricted T cells

The human CD1b protein presents lipid antigens to T cells, but the molecular mechanism is unknown. Identification of mycobacterial glucose monomycolate (GMM) as a CD1b-presented glycolipid allowed determination of the structural requirements for its recognition by T cells. Presentation of GMM to CD1b-restricted T cells was not affected by substantial variations in its lipid tails, but was extremely sensitive to chemical alterations in its carbohydrate or other polar substituents. These findings support the view that the recently demonstrated hydrophobic CD1 groove binds the acyl chains of lipid antigens relatively nonspecifically, thereby positioning the hydrophilic components for highly specific interactions with T cell antigen receptors.

Recognition of a lipid antigen by CD1-restricted alpha beta+ T cells

Major histocompatibility complex (MHC) class I and class II molecules bind immunogenic peptides and present them to lymphocytes bearing the alpha beta T-cell antigen receptor (TCR). An analogous antigen-presenting function also has been proposed for the non-MHC-encoded CD1 molecules, a family of non-polymorphic, beta 2-microglobulin-associated glycoproteins expressed on most professional antigen-presenting cells. In support of this hypothesis, CD1 molecules are recognized by selected CD4-CD8- alpha beta or gamma delta TCR+ T-cell clones, and we have recently shown that CD1 molecules restrict the recognition of foreign microbial antigens by alpha beta TCR+ T cells. But the substantial structural divergence of CD1 from MHC class I and class II molecules, raises the possibility that the antigens presented by the CD1 system may differ fundamentally from those presented by MHC-encoded molecules. Here we report that a purified CD1b-restricted antigen of Mycobacterium tuberculosis presented to alpha beta TCR+ T cells is mycolic acid, a family of alpha-branched, beta-hydroxy, long-chain fatty acids found in mycobacteria. This example of non-protein microbial antigen recognition suggests that alpha beta TCR+ T cells recognize a broader range of antigens than previously appreciated and that at least one member of the CD1 family has evolved the ability to present lipid antigens.

Evaluation of the use of 5-mycoloyl-beta-arabinofuranosyl-(1-->2)-5-mycoloyl- alpha-arabinofuranosyl-(1-->1')-glycerol in serodiagnosis of Mycobacterium avium-intracellulare complex infection

5-Mycoloyl-beta-arabinofuranosyl-(1-->2)-5-mycoloyl-alpha-ar abinofuranosyl-(1-->1')-glycerol, an antigenic glycolipid from the Mycobacterium avium-intracellulare complex (MAC) was examined for its applicability to the serodiagnosis of MAC infection by ELISA. Serum IgM antibody titres against this glycolipid in healthy controls, pulmonary tuberculosis patients and sputum-MAC-culture-negative MAC patients were generally below the cut-off point (ELISA-negative), whereas most of the MAC-culture-positive MAC patient sera were ELISA-positive (93.5%) and their titres were often very high. Thus, high serum IgM titres against this glycolipid may be said to imply that the MAC disease is in an active phase.

Granuloma formation and hemopoiesis induced by C36-48-mycolic acid-containing glycolipids from Nocardia rubra

As previously reported (I. Yano, I. Tomiyasu, S. Kitabatake, and K. Kaneda, Acta Leprologica 2:341-349, 1984), Nocardia rubra, one of the nonpathogenic actinomycetes, possesses three classes of mycolic acid-containing glycolipid, i.e., glucose mycolate, trehalose dimycolate, and trehalose monomycolate. The carbon chain length of their mycolic acids is shorter (C36-48) than that in mycobacteria (longer than C70), and the glycolipid consists of only alpha-mycolic acid. One intravenous administration of 500 micrograms of each purified glycolipid to ICR mice in the form of water-in-oil-in-water emulsion without any protein antigens caused prominent granuloma formation in the lungs, spleen, and liver. The lung index in the treated mice was about 3.5 times larger than that in the control mice (given water-in-oil-in-water emulsion only) at 1 week after the injection and then rapidly declined, while spleen and liver indices peaked at 2 weeks after the injection and persisted longer. The granuloma consisted of macrophages, some of which phagocytized glycolipid micelles, lymphocytes, monocytes, and neutrophils. In addition, many small hemopoietic islands were observed in the liver sinusoids, where various immature blood cells were trapped by the prominent cytoplasmic projections of Kupffer cells. The granuloma formation and hemopoiesis observed here are considered to be the most characteristic morphological expression of macrophage activation in these organs. This is the first report to show that such histological changes can be induced by chemically defined and homogeneous mycolic acid-containing glycolipids other than those of mycobacteria.

Migration of natural suppressor cells from bone marrow to peritoneal cavity by live BCG

Delayed-type hypersensitivity (DTH) responses were suppressed in mice inoculated with bone marrow cells from mice that had been injected with 10(8) colony-forming units (CFU) of live BCG. Upon analysis of this DTH-suppression by the use of a macrophage migration inhibition (MI) assay, the in vitro correlate of DTH, suppressor macrophages in the peritoneal cavity were found to play an important role in DTH suppression. However, neither suppression of DTH nor production of suppressor macrophages was observed in mice inoculated with bone marrow cells from mice that had been injected with methotrexate (MTX), a folic acid antagonist, and 10(8) CFU of live BCG. Moreover, suppressor cells against the MI activity of peritoneal exudate cells from BCG cell wall-immunized mice existed in bone marrow cells from normal mice, natural suppressor (NS) cells, and they were sensitive to MTX. In addition, these NS cells phagocytized carbonyl iron particles, were adherent to Sephadex G-10, and had Fc receptors, but they had no B or T cell markers, suggesting that these cells belonged to a macrophage compartment. From this evidence, we hypothesized that the origin of suppressor macrophages in the peritoneal cavity induced by live BCG injection was MTX-sensitive NS cells in bone marrow, and that these NS cells were stimulated by a small dose of live BCG trapped in bone marrow after i.v. injection of a high dose of live BCG and migrated from bone marrow to the peritoneal cavity.

Regulation of antibody response in different immunoglobulin classes. VI. Selective suppression of IgE response by administration of antigen-conjugated muramylpeptides

The suppressive effect of antigen-conjugated muramylpeptides or 6-O-mycoloyl muramylpeptides selectively on the induction of IgE antibody response was demonstrated. Preadministration of DNP-mycoloyl muramylpeptides completely inhibited the induction of the anti-DNP IgE antibody response with DNP-ovalbumin (DNP-OA). The selective suppression of the IgE response was due to the induction of DNP-specific suppressor T cells by DNP-mycoloyl muramylpeptides, and the suppressor cells were shown to be radiosensitive. Preadministration of OA-conjugated muramylpeptides partially inhibited the primary and secondary induction of an anti-OA IgE antibody response. The suppressor effect was also due to the induction of OA-specific suppressor T cells. Application of allergen-conjugated muramylpeptides as therapeutic agents in human allergic diseases was suggested.

Adjuvant activity of synthetic 6-O-"mycoloyl"-N-acetylmuramyl-L-alanyl-D-isoglutamine and related compounds

Adjuvant and antitumor activities of synthetic 6-O-"mycoloyl"-N-acetylmuramyl-L-alanyl-D-isoglutamine were examined. All the synthetic 6-O-corynomycoloyl-, 6-O-mocardomycoloyl-, and 6-O-mycoloyl-N-acetylmuramyl-L-alanyl-D-isoglutamine were active as adjuvants for cell-mediated immune responses. However, 6-O-mycoloyl-N-acetylmuramyl-L-alanyl-D-isoglutamine was less active as an adjuvant on circulating antibody formation. It was shown that pyrogenic activity of N-acetylmuramyldipeptide was reduced by 6-O-acylation with mycolic acid, but not with nocardomycolic or corynomycolic acid. Tumor-suppression activity was observed by the synthetic 6-O-mycoloyl-N-acetylmuramyl-L-alanyl-D-isoglutamine by using transplantable tumor in syngenic mice.

Adjuvant activity of 6-O-mycoloyl-N-acetylmuramuyl-L-alanyl-D-isoglutamine

Immunological properties of synthetic 6-O-mycoloyl-N-acetylmuramyl-L-alanyl-D-isoglutamine (6-O-mycoloyl-N-acetylmuramyldipeptide) and 6-O-mycoloyl-N-acetylmuramic acid were examined in guinea pigs and mice in comparison with those of BCG cell-wall skeleton, N-acetylmuramyl-L-alanyl-D-isoglutamine, and 6-O-stearoyl-N-acetylmuramyl-L-alanyl-D-isoglutamine. 6-O-Mycoloyl-N-acetylmuramyldipeptide showed a potent adjuvant activity for the induction of delayed type hypersensitivy to N-acetyl-L-tyrosine-3-azobenzene-4'-arsonic acid (ABA-N-acetyltyrosine). It was also found that 6-O-mycoloyl-N-acetylmuramyldipeptide treated with oil droplets or suspended in phosphate-buffered saline was as effective as oil-attached BCG cell-wall skeleton for the generation of cell-mediated cytotoxic effector cells to mastocytoma P815-X2 cells in the spleen of C57BL/6J mice in vivo. However, 6-O-mycoloyl-N-acetyl-muramyldipeptide was less active as adjuvant than BCG cell-wall skeleton and N-acetylmuramyldipeptide in enhancing the circulating antibody formation to T-independent antigen, 2,4-dinitrophenyl-lysyl (DNP-Lys)-Ficoll in vivo, and on the generation of helper function of carrier-primed T-cells, and was inactive as a mitogen on normal mouse spleen cells. On the other hand, although 6-O-mycoloyl-N-acetylmuramic acid was shown to be inactive as adjuvant on immune systems described above, it was active as a mitogen on normal mouse spleen cells.

Immunotherapy with nonviable microbial components

Structural components of microorganisms have been studied for immunopotentiating effect with the aid of transplantable (line 10) tumors in syngeneic guinea pigs. Microbial components were associated with oil droplets, suspended in Tween-saline, and injected intralesionally. BCG cell walls, given in this way, produced regression and cure of 50-60% of established tumors, as did viable BCG. Lipid extraction markedly reduced the tumor-regressing potency of cell walls, but P3, a trehalose mycolate present in the extract, restored full activity to the cell wall residue. P3 alone was nonsensitizing and had no antitumor activity, but it enhanced the latter property of various other microbial products. For example, the cure rates produced by cell walls of M. tuberculosis, M. bovis, M. phlei, or M. smegmatis were enhanced from 20-60% to as much as 90% by addition of P3. P3 also conferred antitumor activity on products from unrelated microbes, such as cell walls of E. coli, and in combination with endotoxins from rough Re mutant salmonellae, it produced cure rates of up to 93%. These results suggest that P3 is essential to the immunopotentiating activity of mycobacteria and that it may be broadly applicable in immunotherapy of cancer with microbial agents.

Mitogenic activity of the cell walls of mycobacteria, nocardia, corynebacteria and anaerobic coryneforms

The mitogenic activity of the cell walls prepared from Mycobacterium bovis BCG, Nocardia rubra, Corynebacterium diphtheriae PW8, and four species of Propionibacterium, Corynebacterium parvum ATCC 11829, Propionibacterium acnes C7, Propionibacterium granulosum ATCC 25564 and Propionibacterium avidum ATCC 25577, were investigated. These cell walls were active as mitogens on normal spleen cells, anti-O sera-treated spleen cells, macrophage-depleted spleen cells of C57BL/6J mice and cortisone-treated thymocytes of C57BL/6J mice. It was also shown that these cell walls were mitogenic on spleen cells and macrophage-depleted spleen cells of congenitally athymic (nude) mice. The above results suggest that the cell walls investigated in this study act as mitogens on both thymus-derived lymphocytes (T-cells) and bone marrow-derived lymphocytes (B-cells).