In this video from Cell Press, human neutrophils are seen phagocytosing the smooth spheres, which are beads coated with a fungal cell wall component, beta-1,6-glucan. (Rubin-Bejerano et al. 2007).
Fungi are eukaryotic heterotrophs that mostly reside in diverse aquatic to terrestrial niches where they function as part of the essential microbial ecosystems that cycle nutrients through the soil, water and atmosphere. Although fungi lack the metabolic diversity of bacteria, they are particularly adept at accessing nutrients through the decomposition of complex polymers found in wood and other plant tissues. Fungi were once classified as plants since they can be often observed growing in soil, but genetic analyses eventually determined they form a unique evolutionary grouping, and are in fact more closely related to animals than to plants. Well known examples are species that produce mushrooms, form part of lichen symbioses, and of course brewer’s yeast. Some species are also facultative and opportunistic pathogens such as Candida albicans and Aspergillus spp.
It seems the human innate immune system has evolved to recognize a structural feature common to most if not all fungal cells. In normal healthy people this can provide a rapid immune response to any potential fungal infection, and is probably why fungal infections are so uncommon despite the fact you are likely inhaling various fungal spores with each breath. The complete immunological story is more complicated than this experimental design encompasses however, as the authors note that fungal cell walls are complex structures composed of not only glucans, but also mannoproteins and other molecules. Intact fungal cell walls actually mask their glucans with mannoproteins, meaning that another as of yet uncharacterized immunological process is likely required to expose the beta-glucans in vivo prior to recognition and destruction.
Rubin-Bejerano I, Abeijon C, Magnelli P, Grisafi P, Fink GR. Phagocytosis by human neutrophils is stimulated by a unique fungal cell wall component. Cell Host Microbe. 2007;2(1):55-67. doi:10.1016/j.chom.2007.06.002