The constituents of the melanin complex from mycelial forms of Fonsecaea pedrosoi were partially characterized. The pigment was mainly accumulated on large alkali-extractable, electron-dense cytoplasmic bodies (melanosomes) and, apparently, on the outer layer of the cell wall as external deposits within verrucose outgrowths. Using electron microscopy and Thiky's periodate/thiosemicarbazide/silver proteinate staining method, glycogenlike particles were also detected at the periphery of the cells. Melanin constituents comprised aromatic and aliphatic/glycosidic structures with a predominance of the latter. Infrared spectra showed the presence of hydroxyl, carbonyl and carboxyl groups. The aliphatic/glycosidic moiety consisted of fatty acids and polysaccharides with protein, in a ratio protein/polysaccharide 1 : 15. Rhamnose, mannose, galactose and glucose (in the ratio 1 : 2: 4: 3.5) were the constituents of the polysaccharide. Lipid components included even-numbered, saturated and unsaturated fatty acids (in the ratio 2: 1) ranging from C16 to Cis. Palmitic and oleic acids were the prominent fatty acids. Aspartic and glutamic acids, leucine, glycine and alanine were the major amino acids. Nonpigmented cells of F.pedrosoi were studied for comparison with the pigmented forms: they did not accumulate acidinsoluble precursors of melanin.

The influence of growth conditions, as well as of propranolol on Fonsecaea pedrosoi morphogenesis was established using the chemically defined media of Czapeck-Dox (CD) and Butterfield (BF). Mycelial growth of F. pedrosoi in both media was obtained at room temperature (25 degrees C) for 14 days, without shaking, whereas conidia formed at 37 degrees C, for 4 days, in shaken cultures and could be isolated free from the mycelium by filtration in gauze. At low pH (2.5-3.0), there appeared sclerotic cells attached to normal hyphae. When propranolol ws added to the CD medium moniliform hyphae were observed, whereas this drug in the BF medium induced formation of sclerotic cells. Ultrastructural examination revealed that the propranolol-induced sclerotic cells were very similar to those observed in infected tissues.

Conidial forms of Fonsecaeapedrosoi, grown under conditions where melanin was or was not synthesized, were allowed to interact with normal and cytochalasin treated macrophages. Melaninfree conidia were more infective to the macrophages. Treatment of macrophages with either cytochalasin B or D before the interaction decreased, but did not totally prevent their infection by the fungi. This inhibitory effect was higher (approximately 90%) if E pedrosoi was grown under conditions where melanin was not synthesized. When melanin-containing conidia were used, the inhibitory effect of the cytochalasin on the infection was lower (approximately 50%). At least two mechanisms of infection of the host cell were observed: typical phagocytosis and another process in which the fungi played a more active role. Infection by E pedrosoi was also observed in the nonprofessional phagocytic MDCK epithelial cell line. Two types of cytoplasmic vacuoles which contained parasites were seen in thin sections of host cells infected with E pedrosoi: a 'tight' type and a 'loose' type. At least 200 conidia-containing vacuoles were analysed by transmission electron microscopy. The 'tight' type was observed in 75% of the vacuoles of non-treated macrophages, suggesting an association with classical phagocytosis. On the other hand, the 'loose' type vacuole was seen in 75% of the vacuoles present in cytochalasin treated macrophages and seemed to be related to induced phagocytosis or active penetration by the fungi.Fonsecaea pedrosoi, a polymorphic pathogenic fungus, is one of the aetiologic agents of chromoblastomycosis, a chronic disease usually limited to the skin and subcutaneous tissue [25]. Tissue forms comprise hypha! segments and brown, thick-walled sclerotic bodies, while culture forms are mainly filamentous with hyphae and conidia. Chromoblastomycosis is thought to be initiated by traumatic implantation of hyphae or conidia into the skin. The disease progresses slowly and any hyphae or conidia inoculated deeply within the skin of a patient tend to disappear so that only sclerotic forms are observed [9]. F. pedrosoi, like other dematiaceous fungi pathogenic for humans, usually forms a dark pigment, generally referred to as melanin, which is deposited on the fungal cell wall and in cytoplasmic structures [1,12].We have already demonstrated that mouse peritoneal resident macrophages have little or no cytotoxic effect on E pedrosoi [13]. During the phagocytic process, melaninpigmented particles are released by the fungus. These particles can be then seen in the same phagocytic vacuoles that contain ingested fungi, as well in other small cytoplasmic vacuoles [13]. It has been suggested that melanin present in the cell wall of fungi, may protect them against destruction by phagocytes, providing resistance to microbial lysis [24].

sites have developed mechanisms for evading this fate. Toxoplasma gondii [12], Mycobacterium leprae [25], Rickettsiae and Chlamydia [29,31] are ingested by macrophages and block the process of L-P fusion, whereas Trypanosoma cruzi disrupts the 373