Electron microscopic studies of complexes of Haemophilus infuenzae, type b, with specific antibodies.

Complexes of cells with and without intact capsular material were prepared with type specific antisera. Thin sections of positively stained specimens were prepared and examined in the electron microscope. In the absence of capsular material the antibodies were observed bound close to one another in the immediate area of the bacterial cell wall. When capsular antigen was present the antibodies were farther separated from one another in the complex and appeared to be attached at random sites along the capsular polymers with occasional individual particles being observed. This positive staining approach appears to be a useful method to observe the molecular structure of precipitated immune complexes.