Fig 2. Microscopic observations of Pneumocystis.

(A, G) Cushion’s data, electron micrsocopy (except [D] and [E] [differential interference contrast], and [F] [Diff-Quik staining, bright field]). (A) A trophic form tightly interdigitated with the host’s alveolar epithelial pneumocytes type I (top arrow). This trophic form also shows fusion with a second trophic form at the level of the cell membrane as well as possibly at the level of the nuclear membrane (middle arrow). (B) Endogeny with four daughter cells within a trophic form. The daughter cells are numbered on the image. Note the absence of cell wall (arrow). (C, D) Rounded ascopsores within an ascus. (E, F) Elongated and condensed ascopsores within an ascus. (G) Collapsed crescent ascus with rounded trophic forms associated. The latter correspond supposedly to released ascopsores. A rent in the ascus cell wall is highlighted by the arrow. (H) Dividing or mating trophic forms; the white rounded structures are supposedly a vacuole (drawn from the electron microscopic image of Fig 4 of [13]). (I) Supposedly mating trophic forms showing fusion of nuclei in dark gray suggesting karyogamy (from Fig 3 of [13]). (J) Karyokinesis within a trophic form; the spindles poles are in dark gray; the white rounded structure is supposedly a vacuole (from Fig 5 of [9]). (K) Synaptonemal complex shown in dark gray in a young ascus (from Fig 2 of [16]). (L) P. murina cell population from resected infected lungs. Green, anti-p57 surface glycoprotein specific to ascospores; magenta, anti-glucan; blue, DNA stained with DAPI. An ascus putatively releasing ascopsores is shown within the boxed area (adapted from [23]). (M) Parentheses-like structures on P. jirovecii asci. The arrow points to this structure of a single ascus. Grocott’s methenamine silver staining (Institute of Microbiology, Lausanne University Hospital). (N) Ascus stained with an antibody conjugated to Alexafluor 594 raised against 1,3-β glucan featuring a circular structure [15]. Alexafluor 594, fluorescent dye; Diff-Quik, modified Giemsa stain; p57, surface glycoprotein with a molecular weight of 57 kDa.