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Absence of FMLP receptors on rat macrophages
B A Walker1, A J Seiler, C A Owens
1University of Michigan Medical School, Department of Pathology, Ann Arbor 48109-0602.
Abstract:
Although rat peritoneal neutrophils in the presence of cytochalasin B demonstrate superoxide (O2-) responses to the chemotactic peptide N'-formyl-met-leu-phe (FMLP), neither elicited rat peritoneal macrophages nor rat alveolar macrophages show an O2- response to FMLP (in the presence or absence of cytochalasin B), although a good O2- response to opsonized zymosan is demonstrated by both types of macrophages. Using Fura-2 loaded cells, peritoneal macrophages failed to show an increase in intracellular calcium after exposure to FMLP, f-nor-leu-phe, F-met-met-met, or F-norleu-leu-phe-norleu-lys. FMLP also failed to induce elevations in intracellular calcium in alveolar macrophages. In 3H-FMLP binding studies, the lack of responsiveness of peritoneal and alveolar macrophages was associated with the lack of FMLP receptors on these cell types, in striking contrast to the presence of functional receptors on rat neutrophils.
Insights
Rat neutrophils respond to chemotactic peptides like N-formyl-methionyl-leucyl-phenylalanine (FMLP), but macrophages do not. Macrophages lack FMLP receptors, explaining their non-responsiveness to these specific immune signaling molecules.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Neutrophils exhibit superoxide (O2-) production in response to chemotactic peptides.
- The role of chemotactic peptides in macrophage activation and signaling pathways is not fully understood.
- Understanding receptor expression is crucial for elucidating cellular responses to external stimuli.
Purpose of the Study:
- To investigate the responsiveness of rat peritoneal and alveolar macrophages to the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP).
- To determine if macrophages possess functional FMLP receptors.
- To compare FMLP-induced responses in macrophages versus neutrophils.
Main Methods:
- Superoxide (O2-) production assays were performed on rat neutrophils, peritoneal macrophages, and alveolar macrophages.
- Intracellular calcium levels were measured using Fura-2 in macrophages exposed to various FMLP analogs.
- Radioligand binding assays (3H-FMLP) were used to quantify FMLP receptor expression on different cell types.
Main Results:
- Rat neutrophils showed O2- responses to FMLP, while peritoneal and alveolar macrophages did not.
- Macrophages did not exhibit increased intracellular calcium levels upon exposure to FMLP or its analogs.
- Macrophages lacked detectable FMLP receptors, unlike neutrophils which possessed functional receptors.
Conclusions:
- Rat peritoneal and alveolar macrophages are unresponsive to FMLP, contrasting with neutrophils.
- The absence of FMLP receptors on macrophages is the primary reason for their lack of response.
- This study highlights differential expression of FMLP receptors and signaling pathways between phagocytic cell types.