Mycobacterial lipoarabinomannan: an extraordinary lipoheteroglycan with profound physiological effects

Detailed structural and functional studies over the last decade have led to current recognition of the mycobacterial lipoarabinomannan (LAM) as a phosphatidylinositol anchored lipoglycan with diverse biological activities. Fatty acylation has been demonstrated to be essential for LAM to maintain its functional integrity although the focus has largely been on the arabinan motifs and the terminal capping function. It has recently been shown that the mannose caps may be involved not only in attenuating host immune response, but also in mediating the binding of mycobacteria to and subsequent entry into macrophages. This may further be linked to an intracellular trafficking pathway through which LAM is thought to be presented by CD1 to subsets of T-cells. The implication of LAM as major histocompatibility complex (MHC)-independent T-cell epitope and the ensuing immune response is an area of intensive studies. Another recent focus of research is the biosynthesis of arabinan which has been shown to be inhibitable by the anti- tuberculosis drug, ethambutol. The phenomenon of truncated LAM as synthesized by ethambutol resistant strains provides an invaluable handle for dissecting the array of arabinosyltransferases involved, as well as generating much needed structural variants for further structural and functional studies. It is hoped that with more systematic investigations based on clinical isolates and human cell lines, the true significance of LAM in the immunopathogenesis of tuberculosis and leprosy can eventually be explained.      

Characterization of the effect of LPS on dendritic cell subset discrimination in spleen

The Gram‐negative bacterial endotoxin lipopolysaccharide (LPS) is a potent inflammatory mediator and a leading cause of bacterial sepsis. While LPS is known to activate antigen‐presenting cells, here we find that LPS down‐regulates expression of CD11c and CD11b on splenic dendritic cell subsets, thus confounding the ability to identify these subsets following treatment. This has implications with regard to tracking the response to LPS in terms of the cell subsets involved, and should be considered whenever such studies are undertaken.     

The Growth of the Shoot Apex of Chenopodium rubrum L. Treated with a Florigenic Extract from Flowering Tobacco Plants: Preliminary Anatomical Observations

Anatomical changes in the shoot apex of Chenopodium rubrum L.treated with an extract from flowering tobacco plants and cultivatedin non-inductive conditions are described. They are comparedwith the anatomy of non-treated vegetative apices and with apicesof plants induced with a short day. Treatment with the extractresulted in both activation of cell division in the upper partof the apex and in apex elongation. Acceleration of leaf primordiainitiation and stimulation of branching took place. The effectcorresponds to the sequence of changes in photoperiodically-inducedplants but is more pronounced. Elongation following 10^–4M GA₃ treatment was of a differentnature; there was only a slight stimulation in the upper partof the apex in contrast with a strong stimulation of growthin length in the lower internodes. These preliminary resultssuggest a similarity between apical changes evoked by a stimulusproduced by short days and an exogenously applied floral stimulus.The changes differed from those caused by exogenous phytohormones. Key words: Chenopodium rubrum, florigen, shoot apex