Potent Inhibition of Neutrophil Migration by Cryptococcal Mannoprotein-4-Induced Desensitization

Abstract

Cryptococcal capsular Ags induce the production of proinflammatory cytokines in patients with cryptococcal meningitis. Despite this, their cerebrospinal fluid typically contains few neutrophils. Capsular glucuronoxylomannan is generally considered to mediate the inhibition of neutrophil extravasation. In the current study, culture supernatant harvested from the nonglucuronoxylomannan-producing strain CAP67 was found to be as potent as supernatant from wild-type strains in preventing migration. We identified capsular mannoprotein (MP)-4 as the causative agent. Purified MP-4 inhibited migration of neutrophils toward platelet-activating factor, IL-8, and fMLP, probably via a mechanism involving chemoattractant receptor cross-desensitization, as suggested by its direct chemotactic activity. Supporting this hypothesis, MP-4 elicited Ca2+ transients that were inhibited by preincubation with either fMLP, IL-8, or C5a, but not platelet-activating factor, and vice versa. Moreover, MP-4 strongly decreased the neutrophil surface expression of L-selectin and induced shedding of TNF receptors p55/p75, whereas CD11b/18 increased. Finally, MP-4 was clearly detectable in both serum and cerebrospinal fluid of patients suffering from cryptococcal meningitis. These findings identify MP-4 as a novel capsular Ag prematurely activating neutrophils and desensitizing them toward a chemoattractant challenge.

Chemotaxis Inhibitory Protein of Staphylococcus aureus Binds Specifically to the C5a and Formylated Peptide Receptor

“…Bordetella pertussis, for example, produces pertussis toxin that inhibits GPCRs by ADP-ribosylation of the G protein (17) and Porphyromonas gingivalis produces a proteinase, which cleaves the C5aR (18). Furthermore, different cell wall components of Cryptococcus neoformans are described to inhibit neutrophil chemotaxis toward IL-8, fMLP, and C5a (19,20), whereas endotoxins of Gram-negative bacteria down-regulate CXC and CC chemokine receptor expression (21,22).…”

O-Acetylation of Cryptococcal Capsular Glucuronoxylomannan Is Essential for Interference with Neutrophil Migration

“…Here, we investigated the contribution of O-acetylation and xylose to the interference of GXM with the chemokinesis of neutrophils (10,11,14) and the process of neutrophil adhesion to the endothelium (20,21). We compared chemically deacetylated GXM and GXM deficient in either O-acetyl or xylose derived from cas1⌬ and uxs1⌬ mutant strains, respectively, with GXM from the corresponding isogenic strains.…”

“…Moreover, in vitro as well as in vivo, GXM has been shown to interfere with the migration of leukocytes toward chemotactic stimuli and inflammatory sites (9 -14), and different mechanisms contribute to this phenomenon. First, cryptococcal GXM impairs neutrophil migration toward chemoattractants (10,11,14), despite adequate stimulation of chemokine production (8,11,15). A combination of the intrinsic chemoattracting properties of circulating GXM (10,16) and down-regulation of chemokine receptors (17) will prevent leukocytes from leaving the bloodstream and migrating toward inflammatory sites.…”

“…Second, polysaccharides interfere with leukocyte adhesion to the endothelium. GXM has been demonstrated to induce L-selectin shedding (14,18), to bind CD18 (19), and to actually impair both phases of neutrophil adhesion to the endothelium, namely the initial rolling (20) as well as subsequent firm binding to the endothelium (21).…”

Production of Extracellular Polysaccharides by CAP Mutants of Cryptococcus neoformans

“…Carbohydrate content ranged between 400 and 4,000 g per fraction, except for GSU growth medium, which was too low to be accurately determined. The purified GXM and GalXM fractions were obtained via different purification protocols (15,20) and enable a comparison of monosaccharide compositions between polysaccharide fractions purified via different methods. ser., serotype; TR, trace.…”