Lipoglycans are putative ligands for the human pulmonary surfactant protein A attachment to mycobacteria - Critical role of the lipids for lectin-carbohydrate recognition

The human pulmonary surfactant protein A (hSP-A) has been implicated in the early capture and phagocytosis of the pathogenic Mycobacterium tuberculosi s by alveolar macrophages. In this report, we examined the interaction of a lveolar proteinosis patient hSP-A with Mycobacterium bovis EGG, the vaccina ting strain, as a model of pathogenic mycobacteria, and Mycobacterium smegm atis, a nonpathogenic strain. me found that hSP-A binds to the surface of M ., bovis BCG;, but also to a slightly lesser extent, to M. smegmatis, indic ating that hSP-A does not discriminate between virulent and nonpathogenic s trains. Among the various glycoconjugates isolated from the mycobacterial e nvelope, we found that the best ligands are the two major lipoglycans: the mannosylated lipoarabinomannan (ManLAM) and the lipomannan, In contrast, th e mannose-capped arabinomannan, structurally close to the ManLAM, as well a s the LAMs from the non pathogenic M. smegmatis are poorly recognized by hS P-A, These results clearly show that the presence of both the terminal mann ose residues and the phophatidyl-myo-inositol anchor are necessary to achie ve the highest binding affinity. Selective removal of either the terminal m annose or the acyl residues esterifying the glycerol moiety of the ManLAM a brogates the interaction with hSP-A, further supporting the notion that the hSP-A recognition of the carbohydrate epitopes of the lipoglycans is depen dent of the presence of the fatty acids.