Identification of Mycobacterium tuberculosis Clinical Isolates with Altered Phagocytosis by Human Macrophages Due to a Truncated Lipoarabinomannan

Abstract

Phenotypically distinct clinical isolates of Mycobacterium tuberculosis are capable of altering the balance that exists between the pathogen and human host and ultimately the outcome of infection. This study has identified two M. tuberculosis strains (i.e. HN885 and HN1554) among a bank of clinical isolates with a striking defect in phagocytosis by primary human macrophages when compared with strain Erdman, a commonly used laboratory strain for studies of pathogenesis. Mass spectrometry in conjunction with NMR studies unequivocally confirmed that both HN885 and HN1554 contain truncated and more branched forms of mannose-capped lipoarabinomannan (ManLAM) with a marked reduction of their linear arabinan (corresponding mainly to the inner Araf-␣(135)-Araf unit) and mannan (with fewer 6-Manp residues and more substitutions in the linear Manp-␣(136)-Manp unit) domains. The truncation in the ManLAM molecules produced by strains HN885 and HN1554 led to a significant reduction in their surface availability. In addition, there was a marked reduction of higher order phosphatidyl-myo-inositol mannosides and the presence of dimycocerosates, triglycerides, and phenolic glycolipid in their cell envelope. Less exposed ManLAM and reduced higher order phosphatidylmyo-inositol mannosides in strains HN885 and HN1554 resulted in their low association with the macrophage mannose receptor. Despite reduced phagocytosis, ingested bacilli replicated at a fast rate following serum opsonization. Our results provide evidence that the clinical spectrum of tuberculosis may be dictated not only by the host but also by the amounts and ratios of surface exposed mycobacterial adherence factors defined by strain genotype.Tuberculosis causes immense morbidity and mortality worldwide (1). The causative bacterium, Mycobacterium tuberculosis, is phagocytosed by and grows within host macrophages. Our recent studies (2, 3) have led to the conclusion that M. tuberculosis is adapting to the human host by cloaking its cell envelope molecules with terminal mannosylated (i.e. Man-␣(132)-Man) oligosaccharides that resemble the glycoforms of mammalian mannoproteins (4). These molecules include the abundant mannose-capped lipoarabinomannan (ManLAM), 2 lipomannan (LM), and phosphatidyl-myo-inositol mannosides (PIMs), which play a central role in M. tuberculosis immunopathogenesis (5). ManLAM and higher order PIMs (i.e. PIM 5 and PIM 6 ) have exposed Man-␣(132)-Man nonreducing termini that engage the mannose receptor (MR) on human macrophages during phagocytosis (3, 6, 7) and dictate the intracellular fate of M. tuberculosis by regulating formation of the unique vesicular compartment in which M. tuberculosis survives within the human host (2, 3).To date, studies of M. tuberculosis phagocytosis have focused largely on use of the common laboratory virulent strains Erdman and H 37 R v and the attenuated strain H 37 R a . Recently, banks of clinical isolates have been characterized in an attempt to link epidemiology and genetic analyses in order to better understand...

Broadening Our View About the Role of Mycobacterium tuberculosis Cell Envelope Components During Infection: A Battle for Survival

“…As a consequence, mycobacteria develop aqueous channels formed by porin molecules in the cell wall structure. Other distinguishing cell wall components of M.tb include ManLAM, LM, PIMs, and a peripheral layer of lipids such as trehalose mycolates (trehalose dimycolate or TDM, trehalose monomycolate or TMM), lipooligosaccharides (LOSs), phenolic glycolipids [PGLs, described in some M.tb clinical isolates (Reed et al, 2004;Torrelles et al, 2008b)], acyl trehaloses (diacylor DAT and triacyl-or TAT), triglycerides and sulfolipids (SLs) (Brennan & Nikaido, 1995;Muñoz et al, 1997aMuñoz et al, , 1997b. Recently, the role for individual components of the cell wall has been elucidated, and much emphasis has been placed on the identification and characterization of various genes that encode enzymes involved in the synthesis of the cell wall constituents.…”

“…PGLs have been found in the Canetti strain of M.tb (Daffe et al, 1987) (PGL-Tb), however, serodiagnostic studies have shown that there were large variations among tuberculous patients in the response to this antigen (Daffe et al, 1991). This is likely due to large differences in phenolglycolipid amounts produced by different M.tb strains (Cho et al, 1992;Torrelles et al, 2008b). Recently, the hypervirulent phenotype observed in several strains of M.tb (i.e.…”

“…In this context, hypervirulent M.tb strains of the Beijing family (Tsenova et al, 2005) are shown to contain large amounts of triglycerides (Reed et al, 2007), and some of them also contain the PGL-TB (Reed et al, 2004). M.tb clinical isolates deficient in ManLAM and PIMs surface exposure, but presenting in their cell wall large quantities of triglycerides, PGL-TB, and dimycocerosates, are also shown to have reduced phagocytosis but faster intracellular growth rate in human macrophages (Torrelles et al, 2008b). These studies performed by Schlesinger and colleagues concluded that the clinical spectrum of TB is not only dictated by the host but also it may be related to the amounts and ratios of specific surface-exposed M.tb adherence factors defined by M.tb strain genotype (Torrelles et al, 2008b;.…”

“…M.tb clinical isolates deficient in ManLAM and PIMs surface exposure, but presenting in their cell wall large quantities of triglycerides, PGL-TB, and dimycocerosates, are also shown to have reduced phagocytosis but faster intracellular growth rate in human macrophages (Torrelles et al, 2008b). These studies performed by Schlesinger and colleagues concluded that the clinical spectrum of TB is not only dictated by the host but also it may be related to the amounts and ratios of specific surface-exposed M.tb adherence factors defined by M.tb strain genotype (Torrelles et al, 2008b;. Is this M.tb genotypic/phenotypic adaptation due to their multiple passages through the host?…”

“…(Torrelles et al, 2008b), and how this may impact the infection outcome . In light of these findings, we need to be careful in considering which cell wall components are heavily present on the surface of the M.tb strain(s) studied and their implications in the host cell phenotype observed.…”