Activation of human neutrophils by Mycobacterium tuberculosis-derived sulfolipid-1

Abstract

The principal sulfatide of a group of acidic lipids from virulent Mycobacterium tuberculosis, sulfolipid-1 (SL-1), stimulates neutrophil superoxide (O2-) generation and, at lower concentrations, primes neutrophil response to several other metabolic agonists including FMLP, and PMA. These responses to SL-1 were examined in relation to diacylglycerol (DAG) generation, Ca2+ availability and activation of guanine nucleotide binding proteins to clarify the signal transduction pathways involved. Pertussis toxin inhibited the ability of SL-1 to both stimulate neutrophils directly and to prime neutrophils for subsequent responses induced by PMA, suggesting a role for one or more guanine nucleotide regulating proteins in both responses. SL-1 induced a rise in neutrophil DAG levels. DAG generation was inhibited by pretreatment of cells with pertussis toxin. Depletion of extracellular Ca2+ ablated O2- release induced by stimulatory levels of SL-1 but did not inhibit the priming effect induced by substimulatory concentrations of the lipid. Investigation of the activation of the neutrophil NADPH oxidase in a cell-free system revealed that the SL-1-priming effect was associated with translocation of the soluble cytosolic factors required for activation of the enzyme. Cytosolic factor translocation was not observed in pertussis toxin pretreated cells. Our results provide evidence for the role of a guanine nucleotide binding protein in both priming and direct activation of neutrophils by SL-1. This G protein regulates both SL-1-induced DAG generation and cytosolic cofactor translocation involved in neutrophil activation and priming. The multiplicity of effects of SL-1 on signal transduction pathways leading to phagocyte activation and priming may exert a profound influence on the pathogenicity of M. tuberculosis.