Photomicrographs of human PBMCs in cultures infected with M fermentans (Mi strain). (A) PBMCs cultured in suspension without infection of mycoplasma for 5 days. Some macrophages attached to the surface of the flask. (B) PBMC culture infected by mycoplasma for 4 weeks. Small clumps of cell aggregates were found in culture, and these cells later became immortalized. (C) PBMCs in a culture infected by mycoplasma for 8 weeks. The rapidly proliferating cells formed large cell aggregates. (D) PBMCs immortalized by mycoplasmal infection after 4-month culture. Many of the rapidly dividing cells became individually separated, many others aggregated into small clumps. Original magnification × 100 (A-B,D) and × 40 (C). The images were captured on an inverted phase contrast microscope Nikon Diaphot (Nikon, Tokyo, Japan) equipped with a Polaroid camera Nikon UFX-II and Photo Eyepiece objective lens CF PL 2.5× (Nikon). Original magnification was × 80 (A, B, D) and × 40 (C), under an achromatic objective lens with numerical aperture of 0.4 and 0.3, respectively.