Talaromyces marneffeilaccase modifies THP-1 macrophage responses

Abstract

Talaromyces (Penicillium) marneffei is an emerging opportunistic pathogen associated with HIV infection, particularly in Southeast Asia and southern China. The rapid uptake and killing of T. marneffei conidia by phagocytic cells along with the effective induction of an inflammatory response by the host is essential for disease control. T. marneffei produces a number of different laccases linked to fungal virulence. To understand the role of the various laccases in T. marneffei, laccase-encoding genes were investigated. Targeted single, double and triple gene deletions of laccases encoding lacA, lacB, and lacC showed no significant phenotypic effects suggesting redundancy of function. When a fourth laccase-encoding gene, pbrB, was deleted in the DlacA DlacB DlacC background, the quadruple mutant displayed delayed conidiation and the conidia were more sensitive to H 2 O 2 , sodium dodecyl sulfate (SDS), and antifungal agents than wild-type and other transformants. Conidia of the quadruple mutant showed marked differences in their interaction with the human monocyte cell line, THP-1 such that phagocytosis was significantly higher when compared with the wild-type at one and 2 hours of incubation while the phagocytic index was significantly different from 15 to 120 minutes. In addition, killing of the quadruple mutant by THP-1 cells was more efficient at 2 and 4 hours of incubation. The levels of the proinflammatory cytokines TNF-a, IL-1b and IL-6 from THP-1 cells infected with the quadruple mutant were also significantly increased in comparison with wild-type. The results demonstrate that production of laccases by T. marneffei actually promotes the pathogen's resistance to innate host defenses.

Laccase Properties, Physiological Functions, and Evolution

“…To understand the role of laccase in virulence of T. marneffei, single, double, triple, and quadruple deletions of genes encoding lacA, lacB, lacC, and pbrB laccases were obtained. Only conidia from the quadruple mutant showed increased sensitivity to the antifungal agents and vulnerability to phagocytosis and killing by monocyte cell line THP-1 [188,190]. These results suggest that the laccase of T. marneffei promotes resistance of this pathogen to host immune defenses [188].…”

“…Only conidia from the quadruple mutant showed increased sensitivity to the antifungal agents and vulnerability to phagocytosis and killing by monocyte cell line THP-1 [188,190]. These results suggest that the laccase of T. marneffei promotes resistance of this pathogen to host immune defenses [188]. The pigment or other laccase products reduce immune recognition, potentially interfering with signaling pathways in monocytes [190].…”

“…Infection of AIDS patients caused by Talaromyces marneffei suggests a potential role of laccase in the virulence of this opportunistic pathogen [188][189][190]. A possible mechanism is associated with the production of a red soluble pigment by both yeast and mold forms of T. marneffei.…”

Role of laccase in the virulence ofTalaromyces marneffei:A common link between AIDS-related fungal pathogens?

“…For example, AIDS-related responses to C. neoformans have a minimal, but retained macrophage signaling component that contributes significantly to pathology during anti-retroviral-associated immune reconstitution syndromes. 24,25 Degradation of these residual macrophage responses by fungal laccases as demonstrated by Sapmak et al, 21 may thus provide a key common factor in determining the prevalence of laccase-expressing fungal pathogens in AIDS-related infections. Thus, further study of laccases in T. marneffei may provide molecular and immunological clues as to why saprophytic organisms have become such potent AIDS-related pathogens.…”

“…Thus, in the present study, Sapmak and collegues 21 undertook the formidable task of constructing a quadruple mutant of the fungus, to test the role of laccases in the virulence of the organism. Despite the technical challenges of such transformations in T. marneffei genetic backgrounds, for which limited experience (and transformation markers) existed for the fungus, deletion strains were obtained after multiple transformations which showed robust wild-type growth rates.…”