Figure 2. HIV infecting a mucosal site. HIV particles (red) can penetrate the epithelium of the female genital tract as early as a few hours after infection. This microscopic image shows a section of human ectocervical tissue from routine hysterectomy surgery that was exposed to HIV in vitro for four hours. The cell nuclei are shown in blue and the cell surfaces in green. This image was provided by the laboratory of Tom Hope at Northwestern University.