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Differentiation stimuli induce receptors for plasma fibronectin on the human myelomonocytic cell line HL-60
Abstract:
Plasma fibronectin (Fn) induces phagocytosis of C3b-opsonized sheep erythrocytes (EC3b) by human peripheral blood monocytes. However, Fn does not induce erythrophagocytosis of EC3b by human polymorphonuclear leukocytes (PMN), unless the PMN have been exposed to C5a or N-formyl-methionyl-leucyl-phenylalanine. Because of this difference, it is of great interest to examine Fn binding to cells that possess the capacity to differentiate into either granulocytes or monocytes. Hence, we have examined the consequences of Fn binding to the human myelomonocytic cell line, HL-60, both before and after in vitro differentiation of the HL-60, along a monocytoid or a granulocytoid pathway. Fn receptors were not found on undifferentiated HL-60, but several differentiating agents promoted the HL-60 binding of Fn-coated microspheres (Fn-ms). The peak of Fn-ms binding occurred four to five days after the induction of differentiation with dimethylsulfoxide (DMSO), and two days after induction by PMA. In addition, cells that differentiated along either the monocytoid or the granulocytoid pathway showed a marked increase in the phagocytosis of both IgG-coated erythrocytes (EA) and EC3b when they were exposed to Fn. Comparison of the effects of anti-Fn monoclonals on the binding of Fn-ms to the monocytes, PMN, and HL-60 showed that the same monoclonals block Fn-ms-binding and Fn-induced EC3b phagocytosis by all three cell types. Two monoclonal antibodies, M1/70 and A6F10, directed against membrane antigens on PMN and monocytes, inhibited Fn-ms binding. Both also blocked Fn-induced EC3b ingestion by these cells. However, neither antibody blocked Fn-ms binding or EC3b ingestion by differentiated HL-60. We conclude that differentiated HL-60 cells express functionally active Fn receptors, similar to monocytes and activated PMN, which, nonetheless, differ from normal cells in their association with the antigens recognized by M1/70 and A6F10.
Insights
Plasma fibronectin (Fn) enhances phagocytosis by monocytes but not resting PMNs. Differentiated HL-60 cells, like monocytes and activated PMNs, bind Fn and increase phagocytosis, suggesting distinct Fn receptors.
Area of Science:
- Immunology
- Cell Biology
Background:
- Plasma fibronectin (Fn) is crucial for phagocytosis, particularly of C3b-opsonized targets by monocytes.
- Human polymorphonuclear leukocytes (PMN) require activation (e.g., by C5a) for Fn-mediated phagocytosis, unlike monocytes.
Purpose of the Study:
- To investigate fibronectin (Fn) binding and phagocytosis in the human myelomonocytic cell line HL-60.
- To compare Fn interactions with undifferentiated and differentiated HL-60 cells, mimicking monocyte and granulocyte pathways.
Main Methods:
- Utilized HL-60 cells, inducing differentiation with dimethyl sulfoxide (DMSO) or PMA.
- Assessed fibronectin-coated microsphere (Fn-ms) binding and phagocytosis of IgG-coated erythrocytes (EA) and C3b-opsonized erythrocytes (EC3b).
- Employed anti-fibronectin monoclonal antibodies and antibodies (M1/70, A6F10) against PMN/monocyte antigens to analyze receptor function.
Main Results:
- Undifferentiated HL-60 cells lacked Fn receptors, but differentiation induced significant Fn-ms binding.
- Differentiated HL-60 cells, along both monocytoid and granulocytoid pathways, showed enhanced phagocytosis of EA and EC3b upon Fn exposure.
- Anti-fibronectin antibodies blocked Fn-ms binding and phagocytosis in monocytes, PMNs, and differentiated HL-60 cells.
- Monoclonal antibodies M1/70 and A6F10 inhibited Fn-ms binding and phagocytosis in monocytes and PMNs but not in differentiated HL-60 cells.
Conclusions:
- Differentiated HL-60 cells express functional fibronectin receptors involved in phagocytosis.
- These receptors on differentiated HL-60 cells appear distinct from those on normal monocytes and PMNs due to their differential association with M1/70 and A6F10 antigens.