In vivo chemotaxis of rat leukocytes in the presence of circulating chylomicrons

Dietary-induced chylomicronemia was produced in rats to determine its effect on the chemotactic activity of ⁵¹Cr-labelled adoptively transferred isologous leukocytes. Rats fed a low protein high fat diet for 2 months had normal total plasma cholesterol and triglyceride levels, but increased amounts of chylomicrons. Circulating neutrophils and monocytes from animals on a normal diet were able to phagocytose chylomicrons from plasma of those animals on the special diet. Peritoneal exudate cells from the latter animals contained intracellular chylomicrons demonstratable both histologically and biochemically. Neutrophils and mononuclear cells from normal or special fed animals, when transferred to chylomicronemic recipients, had a reduced ability to accumulate at the site of a complement-dependent inflammatory reaction but circulated normally. The defective chemotactic activity observed could be duplicated when cells were allowed to ingest aggregated protein instead of chylomicrons. It was concluded that circulating leukocytes ingest chylomicrons from the plasma with a resultant reduction in their chemotactic activity. The results were discussed in relation to the increased incidence of infection in diabetes characterized by Type I and V hyperlipidemias. It was also suggested that phagocytosis of particulate substances by entrapped leukocytes in atherosclerotic lesions would induce phagocytic enzyme release which could contribute to the eventual destruction of the vascular wall.