Biochemical basis for the killing ofCryptococcus neoformansby rat peritoneal cells

Abstract

The biochemical basis of peritoneal cell cytotoxicity for (,'ryptoc~Jccus ne~/brmans was studied by, meast.ring the killing of the yeast by' peritoneal resident cells and peritoneal exudate cells obtained from normal and proteose peptone-rejected animals, respectively. Bolfi cell populations killed ('. ,e~?/brmcm.v to an equivalent extent after 3 h incubation. Exudale cells showed anti-cryptococcal activity from the first hour of" incubation. ~hile no killing was observed with resident cells betk~re 3 h. Both ceil populations triggered a respiratory burst in response to opsonized ('. He~/~Jrmcm,v as indicated by, the fact that killing of the yeast was inhibited by' scavengers of reactive oxygen intermediates {ROD. C. ,eqibrmans susceptibility to H2()~ alld hydroxyl radicals in cell-free systems is demonstrated by, incubating a yeast suspension with different concentrations of H_~O2 and Fenton's reagents, respectively'. These restllts suggest that oxygen metabolites play an active role in ('. ne0/i,mans killing.Cryptococcus neoformans is a pathogenic yeast causing disease predominantly in immunosuppressed patients [21,22]. Since the beginning of the human immunodeficiency virus epidemic the frequency of cryptococcosis has increased dramatically and constitutes a significant medical problem because the mechanisms of host defence against C. neoJbrmans are not well understood [6]. Clinical and experimental studies have shown that an adequate cell-mediated immune (CMI) response is critical for effective host defence against cryptococcosis [5,13]. Much research has been directed at determining the specific cell phenotype(s) ultimately responsible for effector cell activity against C. neoformans. Hill [13] has demonstrated that CD4 + T-cells caused multinucleated giant cells to form around C neq/brmans and confine the yeast within the primary site of infection in the respiratory tract, lnterferon-?,-activated rat alveolar macrophages showed anti-cryptococcal activity [21]: human peripheral blood mononuclear cells stimulated with heat-killed C neoJormans in vitro and then challenged with an inoculum of live C. neoformans, killed the encapsulated organism better than unstimulated cells [16]. Natural killer (NK) cells [12] have demonstrable activity against C. neoformans in in vivo murine models. On the other hand, T-suppressor cells have been reported to be induced by C neoformans in rat and murine models [4,19,20,25]. These results suggest that the CMI response to cryptococcal antigen is a complex sequence of events and involves multiple cell populations and soluble factors.Killing of C neoformans has been reported by several authors using different cell populations [61,21], even though the biochemical basis of cytotoxicity for the encapsulated yeast remains obscure. Phagocytes, such as neutrophils and macrophages, undergo an oxidative burst in response to phagocytic or membrane stimuli with the generation and release of a variety of reactive oxygen intermediates (ROD. This 405 Med Mycol Downloaded from informahealthca...

Mechanisms for Induction of Immunosuppression during Experimental Cryptococcosis: Role of Glucuronoxylomannan

“…We also observed that following infection there is a change in the behavior of the population in the accessory cells, as reflected by the modification of several functions, such as phagocytosis, lytic activity, and antigen presentation (26). On the other hand, we observed killing of C. neoformans by an NADPH oxidase-dependent mechanism (27). We have recently demonstrated that the proliferative response to mitogens of spleen mononuclear (Spm) cells from C. neoformans-infected rats dramatically decreased in the suppressor period postinfection (28).…”

“…Cultures were grown on Sabouraud glucose agar slants at 37°C, maintained by weekly subculture on the same medium, and periodically checked for assimilation pattern, urease production, and virulence. For each infection, yeast cells were harvested from a 3-day culture at 37°C and the precise number of viable cells was determined by triplicate counting of the colony forming units (CFU) on Sabouraud agar after 48 -72 h of incubation at room temperature (27).…”

An Innate Immune System Cell Is a Major Determinant of Species-Related Susceptibility Differences to Fungal Pneumonia

“…These studies were performed with AM from normal noninfected rats in the absence of exogenous cytokine stimulation and would appear to highlight intrinsic differences between rat and mouse AM. Oxidative killing of C. neoformans is an important mechanism of action for immune effector cells (30,31). Rat AM incubated with catalase and superoxide dismutase showed an increase in cryptococcal lysate fungal burden, suggesting the importance of H 2 O 2 and reactive oxygen intermediates in limiting intracellular growth.…”

Rat eosinophils stimulate the expansion of Cryptococcus neoformans-specific CD4+ and CD8+ T cells with a T-helper 1 profile

“…6 Moreover, the NADPH oxidase system was also found to be very important in the mechanism of C. neoformans killing by rat peritoneal cells, with the superoxide anion, hydrogen peroxide (H 2 O 2 ) and the hydroxyl radical being involved in this process. 7 Eosinophils, in contrast, are implicated as effector cells in helminthic infections, releasing their many cytoplasmic granules, containing toxic molecules, in response to antigenic stimuli. 8 Moreover, they notably contribute to allerAna P. Garro, Laura S. Chiapello, José L. Baronetti and Diana T. Masih…”