Scanning electron microscopy of guinea pig alveolar macrophages: in vitro phagocytosis of Mycoplasma pneumoniae.

The scanning electron microscopic appearance of guinea pig alveolar macrophages during in vitro antibody-mediated phagocytosis of Mycoplasma pneumoniae is described. This study utilizes the ability of M. pneumoniae to attach to and replicate on a glass cover slip surrounding a monolayer of macrophages without inducing phagocytosis despite multiple points of interaction between organisms and macrophage filopodia. The addition of specific anti-M. pneumoniae serum to this system evokes a sequence of macrophage surface morphologic changes accompanied by engulfment of the surrounding mycoplasmas. The sequence of changes occurring over the 90 minutes subsequent to the addition of antiserum were visualized well with the scanning electron microscope and included the early appearance of elongated, rigid filopodia, the internalization of M. pneumoniae by ruffled membrane extensions, and finally the appearance of highly spread cells surrounded by large areas of cover slip cleared of M. pneumoniae.