Specific immunoglobulin from the sera of patients with antibodies to Aspergillus and from antisera raised in rabbits to Aspergillus fumigatus fractions bound almost exclusively to the mycelial wall, as shown by immunogold labelling of ultra-thin sections. Different layers of the wall were labelled, depending on the source of the antigen used to produce antibody. Internal, cytoplasmic components were generally not labelled, except with antisera raised to crude wall material and to a Concanavalin A (ConA)-binding fraction of a water-soluble preparation.Numerous antigens have been obtained from Aspergillus fumigatus mycelium by cell breakage followed by separation and fractionation of water-soluble and wall extracts [1,2,8,14,20]. These water-soluble antigens are frequently called 'intracellular' extracts without any demonstration of their localization. With Candida albicans and Cladosporium cladosporioides, it has been shown that wall antigens are released by cell disruption and are present in the water-soluble extract [4,16].There have been very few studies which have dealt with the cellular localization of A. fumigatus antigens. Mycelial surface structures have been used as antigens to detect specific anti-Aspergillus antibodies by indirect immunofluorescence techniques [5,21].Using cryosections of formaldehyde-treated mycelium as antigens, reactivity of sera from human subjects was shown to involve both wall and cytoplasmic components by indirect immunofluorescence [19]. These studies indicated that the whole mycelium (inner and outer walls and cytoplasm) contains reactive antigens.Previously, antisera raised in rabbits to partially purified fractions of A. fumigatus were shown to differ in their ability to bind to surface antigens of the intact mycelium [6, 13]. The antisera also recognized different antigenic moieties in A. fumigatus preparations when analysed by combined SDS-PAGE and immunoblotting [10]. These antisera, when used in conjunction with immunoelectronmicroscopy (IEM), could serve as tools to identify different antigens and their subcellular location in the mycelium. At the same time, binding studies with sera from patients with aspergillosis would help to pinpoint immunodominant antigens. 73 Med Mycol Downloaded from informahealthcare.com by McMaster University on 12/26/14For personal use only.