FIG 1.

Plasmodium sporozoites (SPZs) primarily invade the distal lateral lobes. Representative images of the entire depth (maximum intensity projection [MIP]) or partial depth (subset MIP) or single-slice confocal images of salivary glands (SGs) stained with DAPI (DNA, red), WGA (chitin/O-GlcNAcylation, blue), and either GFP (panels A and C to D; SPZs, green) or CSP (panel B; a SPZ protein, green) 18 to 24 days postinfection with P. berghei. Scale bar length units are micrometers. (A) Low and high magnification of SG with only the distal lobes infected and showing where SPZs were found: in secretory cell cytoplasms (panel ii, arrows), in secretory cavities (panel ii, arrowheads), in large, central, fluid-filled lumens (panel iii, arrows), in locations associated with the basement membrane (panel iv-vi, arrows), and rarely, inside the salivary duct (panel iv inset, arrow). The contrast in the inset in panel iv was uniformly enhanced to highlight the salivary duct SPZ and in panels v to vi to highlight the SPZs and secretory cell cytoplasms. The basement membrane (from the DIC channel; not shown) is marked by a dashed line (panels v and vi). (B) Representative images of PL (panel i) and M (panel ii) lobe infections. Multiple SPZs are observable (asterisks). (C) Number of lobes of different types imaged in this study (top) and number of SG lobes harboring parasites out of total infected SGs (bottom). (D) Total lobes imaged (left) and number of lobes imaged from uninfected SGs (right). (E) SG SPZ numbers differed from lobe to lobe, even within a single mosquito. A single SPZ was observed in one DL lobe (panel ii), in proximity to a fused salivary duct (panel iii). In another DL lobe from that mosquito, about 10 SPZs were oriented toward an irregular, round lumen (panel iv, arrow). Some infected lobe regions contained accumulations of what was likely shed CSP (panel iv, asterisk). (F) Representative image from a SG with secretory cell cytoplasms filled with SPZs (see the full lobe image in Fig. 4A and the description in the corresponding figure legend) that was used to determine that ∼40 sporozoites can occupy the cytoplasmic volume of a typical SG secretory cell (n = 25 cells). In this lobe, SPZs inside secretory cavities (slice image, asterisks) were easily discernible and were excluded from cytoplasmic SPZ counts. Two cells are outlined in white dashes. (G) Frequency and distribution of SPZs observed inside the salivary duct.