Circadian structure of rat neutrophil phagocytosis

Abstract

Published findings regarding the time structure of phagocytosis appear to be partly discordant. In addition, this feature has not yet been evaluated in rats, although the rat is an important biomodel used for haematological preclinical biomedical studies. Thus, we examined selected characteristics using rats in order to help elucidate the above-mentioned controversies and to provide further complete data on the haematology of this biomodel. The ingestion of foreign particles (HEMA) or large cells (yeast), the reduction of nitroblue tetrazolium salts (NBT) in rat circulating neutrophils and their migration were evaluated. We found circadian variations in the following characteristics of neutrophil phagocytosis: (i) phagocytic activity; the concentration of engulfed particles and phagocytic index decreases late in the day and peaks in the morning; (ii) NBT reduction; a rise being observed at noon and a fall in the evening. The acrophase for phagocytosis of larger yeast cells was earlier (small hours) than that of smaller HEMA particles (in the morning). Chemotactically oriented migration showed a significant increase in the afternoon, but we have not found a statistically significant fit for the cosine function of this characteristic. No circadian rhythm was present in spontaneous migration. Our findings support the opinion that changes in phagocytic characteristics are a part of the circadian system of the immune system in laboratory rats. By comparing our data with the literature it seems that discrepancies in the courses of the circadian rhythms can be at least partly caused by different laboratory procedures as well as by different acrophases for the various elements of phagocytosis.