Phagocytosis is the most important and initial defense against many pathogens in mammals. In order to verify the efficiency of the immune system it is possible to examine the functionality of the phagocytes. The phagocytosis test enables a quantitative analysis of phagocytic function of neutrophils and monocytes in a blood sample using e.g. flow cytometry. The assay can measure the overall percentage of monocytes and neutrophils showing phagocytosis (ingestion of one or more bacteria per cell) and the individual cellular phagocytic activity (relative number of bacteria per cell). Six captive harbor seals of different sex and age were tested in January, March, August and December of 2005, and four were tested again in January 2008. All test results were considered in the statistical tests. A Phagotest® test kit produced by Orpegen Pharma (Czernyring 22, 69115 Heidelberg, Germany) was applied. The analysis was performed based on statistical results provided by the supplied software CellQuestPro® (Becton Dickinson). For reference, together with the Phagotest®, the differential hematology profile was checked, as well as hemochemistry, which in all cases were normal. All six animals showed an increase of phagocytosis in neutrophils and monocytes during the year. In January the mean of phagocytic activity in neutrophils was 67%, in March 80%, in August 86% and in December 93%. A similar trend could be seen in monocytes (Figure 1). Thus, there seems to be an annual trend. Random tests in subsequent years supported the initial findings of seasonal changes. Some results of neutrophil phagocytosis in the animals could be classified as below normal (<80%). Abnormal phagocytic activity can occur with a variety of clinical disorders.2,4 The defects can be associated with the neutrophil itself or with an immunoglobulin or complement defect. Acquired defects associated with altered phagocytic activity can be observed for example in trauma, renal dysfunctions, and particularly infections. Phagocytosis has also been shown to be affected by numerous xenobiotics, such as dieldrin, mercury, cadmium and lead.1,3 As the latter factors can probably be excluded as other hematology values were normal, higher physiological stress might play a role in the rising phagocytic activity. To evaluate the trend, another series is planned for 2009/2010.
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Trend of phagocytic activity of neutrophils (left) and monocytes (right) of captive harbor seals from January to December.
The authors would like to thank Dr. Jörg Driver for his support as well as the team of the Seal Rehabilitation Center Friedrichskoog.
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