Crystals in atherosclerotic lesions: real or artefact?

Atherosclerotic lesions were obtained from man during surgery and from cholesterol-fed rabbits. They were maintained at about 37 degrees C during handling. Smears were prepared on glass slides and these were examined microscopically at 37 degrees C. Solid rhomboidal or thick needle-like crystals were present at 37 degrees C but increased in numbers or in size or both on cooling. Staining studies and measurement of melting point (133-153 degrees C) suggested that such crystals are composed largely of free cholesterol or a related sterol. Liquid crystals exhibiting conic focal (Maltese cross) anisotropism were present at 37 degrees C and did not appreciably increase in either size or numbers on cooling. Staining studies and their resistance to digitonin suggested that these Maltese cross crystals are largely esterified cholesterol. Thin needle-like crystals arranged like feathers or in rosettes were seen in smears of adipose tissue and were attributed to triglycerides.