Abstract
BackgroundThe innate immune response constitutes the first line of defense against invading pathogens and consists of a variety of immune defense mechanisms including active endocytosis by macrophages and granulocytes. Endocytosis can be used as a reliable measure of selective and non-selective mechanisms of antigen uptake in the early phase of an immune response. Numerous assays have been developed to measure this response in a variety of mammalian and fish species. The small size of the zebrafish has prevented the large-scale collection of monocytes/macrophages and granulocytes for these endocytic assays.Methodology/Principal FindingsPooled zebrafish kidney hematopoietic tissues were used as a source of phagocytic cells for flow-cytometry based endocytic assays. FITC-Dextran, Lucifer Yellow and FITC-Edwardsiella ictaluri were used to evaluate selective and non-selective mechanisms of uptake in zebrafish phagocytes.Conclusions/SignificanceZebrafish kidney phagocytes characterized as monocytes/macrophages, neutrophils and lymphocytes utilize macropinocytosis and Ca2+-dependant endocytosis mechanisms of antigen uptake. These cells do not appear to utilize a mannose receptor. Heat-killed Edwardsiella ictaluri induces cytoskeletal interactions for internalization in zebrafish kidney monocytes/macrophages and granulocytes. The proposed method is easy to implement and should prove especially useful in immunological, toxicological and epidemiological research.
Highlights
The zebrafish, one of the most popular animals of developmental biologists, is rapidly gaining ground as an infection and immunology model [1,2,3]
Characterization of zebrafish leukocytes When hematopoietic cells of zebrafish were evaluated by flow cytometry, three distinct non-erythrocyte cell populations were electronically separated according to their size (FSC) and granularity (SSC) (Figure 1A): 1) macrophage/monocytes and granulocytes, 2) hematopoietic precursors, and 3) lymphocytes and lymphocyte-like cells
Studies in which microscopic assessment of phagocytosis in head kidney granulocytes of fresh water fish were compared to the flow cytometry method reported accurate correlations between procedures [43,44]
Summary
The zebrafish, one of the most popular animals of developmental biologists, is rapidly gaining ground as an infection and immunology model [1,2,3]. Cells of the monocyte/ macrophage and granulocyte lineage are important elements of the immune defense system. These cells take up and destroy non-self damaged or apoptotic cells. Even though our main focus lies in the role of zebrafish monocytes/ macrophages and granulocytes for disease control, we included data supporting and expanding the findings by Li et al (2006) [19] on the endocytic abilities of teleost B cells. The innate immune response constitutes the first line of defense against invading pathogens and consists of a variety of immune defense mechanisms including active endocytosis by macrophages and granulocytes. The small size of the zebrafish has prevented the large-scale collection of monocytes/macrophages and granulocytes for these endocytic assays
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