Identification of small cells in fetal and infant adipose tissue.

In developing adipose tissue, cells of size less than 25 micron may make a major contribution to adipose tissue cell populations. This study reports the separation, identification, and sizing of infant and foetal adipose tissue small cells. Subcutaneous adipose tissue was taken from the anterior abdominal wall of children aged 2 months and 22 months. Subcutaneous tissue was also obtained from a paraumbilical site in 4 fetuses of gestational age 16 weeks. Tissue samples were fixed in buffered osmium tetroxide solution containing collidine. Aliquots of cell preparations suspended in saline on microscope slides were viewed and separated using a dissecting microscope. A diameter distribution of particle size was obtained using at least 200 cells for each preparation. There was a substantial number of cells that were smaller than 20 micron. Their modal cell size was remarkably constant in fetuses and in 2-month-old and 22-month-old infants. Ultrastructural studies show that the tissue is composed of a relatively uniform population of cells within sparsely collagenous connective tissue. Although some of the cells show no intracytoplasmic aggregates of lipid material, others show variable amounts of lipid material which can occupy a very large part of the cell volume.