Osmiophilic cytoplasmic inclusions in the lymph node post-capillary venules of the guinea pig.

A hitherto unknown pleomorphic osmiophilic inclusion was found in te endothelial cells of the guinea pig lymph node post-capillary venules; its diameter ranges from 0.4 to 2.2 micrometers, it is bound by a single membrane and consists of heavily dense granular area interrupted by irregularly spaced light bands. Occasionally, irregularly arranged membranous profiles in the granular matrix are also seen. It appears that the formation of this unique inclusion is related to the sex hormonal environment but its significance is yet unknown.