The role of the complement system in the neutrophil functions stimulatedin vitroby an alkali-insoluble cell wall fraction ofParacoccidioides brasiliensis

Abstract

We investigated the capacity of an alkali-insoluble cell wall polysaccharide fraction (FI) ofParacoeeidioides brasiliensis to induce rat polymorphonuclear neutrophil (PMN) migratory and chemiluminescence (CL) responses. Normal rat serum pre-incubated with F1 induced a chemotactic neutrophil response which was fully abolished by heat-inactivation. The participation of the alternative complement pathway was more effective than that of the classical pathway since depletion of factor B by heating at 50°C reduced PMN migration, whereas blockade of the classical pathway with EGTA left the migratory response practically unchanged. Opsonized serum F 1 induced a significant release of oxygen radicals from PMN as measured by CL. The complement system was also found to be involved in this activity since serum inactivation at 56°C altered the CL response. In addition to complementderived fragments, other serum opsonins, probably cross-reacting antibodies, were required for optimal interaction between PM N and opsonized particles. These results contribute to the understanding of the role of fungal components and of the complement system in the inflammatory response observed in paracoccidioidomycosis.Paracoccidioidomycosis or South American blastomycosis is a deep mycosis caused by the dimorphic fungus Paracoccidioides brasiliensis and is the most widespread systemic mycosis in South America [23]. The role of phagocytic cells in the host defense against this fungus is still not well understood. The importance of polymorphonuclear neutrophils (PMN) has been suggested by the finding of a massive infiltration of these cells at the inflammatory sites during the initial stage of the disease in man [12] as well as in experimentally infected animals [3,37]. The presence of PMN has also been detected in the suppurative region of the granulomatous lesions characteristic of the chronic phase of this mycosis [4,11]. A similar inflammatory response was also observed when animals were injected with isolated components of the fungus cell wall such as lipids and polysaccharides [36,37], suggesting that these substances may play an important role in the virulence and pathogenicity of P. brasiliensis. One of these components, the alkali-insoluble polysaccharide fraction (F1),was able to induce accumulation of PMN during the early phase of the inflammatory response in experimental models [3,11]. Furthermore, the F 1 fraction was shown to be able to activate the classical and alternative complement pathways of rats both in vivo and in vitro (L. S. P. Crott, R. T. P. Sobreira, C. L. Silva & J. E. Barbosa, unpublished results).

Structural and immunological studies of a pectin and a pectic arabinogalactan from Vernonia kotschyana Sch. Bip. ex Walp. (Asteraceae)

“…Through such activation, polysaccharides have shown to be able to increase leukocyte migration in vitro when incubated in the presence of serum. 44 In contrast to chemotaxis mediated by activation of complement, our study showed that both Vk100A2a and Vk100A2b were able to stimulate human leukocyte migration, independent of complement (Figs. 6 and 7).…”

The Paracoccidioides Cell Wall: Past and Present Layers Toward Understanding Interaction with the Host

“…Complement activation (Crott et al, 1997) and neutrophil chemotaxis (Crott et al, 1993) stimulated by F1 have been observed. It has been demonstrated by immunofluorescence that C3, C3a, C3d, C3g, C4, C5b-9, and factors H and B are present on the cell surface of P. brasiliensis yeasts (Munk and Silva, 1992) and that complement 3 and mannose receptors are important for phagocytosis by macrophages (Jiménez et al, 2006).…”